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Raiders of the Lost Canal: Review of Underrecognized Skull Base Canals, Fissures, and Foramina
Abstract
The anatomy of the skull base is complex and poses a daunting challenge to many radiologists and trainees. In addition to knowing major skull base passages, there are several underrecognized skull base canals, foramina, and fissures that are critical to avoid misdiagnosis, understand the spread of disease, and guide surgical management. A review of the current literature on these forgotten structures yielded numerous original articles and a few review articles, none of which were comprehensive. This article aimed to fill that void. We provide a comprehensive review of underrecognized skull base anatomic structures and their content and discuss their clinical implications.Learning Objective: Recognize uncommon skull base structures, their content, and their clinical implications
... Apart from the common foramina of the skull base, there are several other, rarely found foramina that have been identifi ed as anatomical variations. This includes canalis basalis medianus (CBM), foramen meningo-orbitale, craniopharyngeal canals, palatovaginal canals, foramen of Vesalius and canaliculus innominatus [3,4]. The majority of these variations result from the typical developmental process and their presence is primarily determined genetically [5]. ...
Objectives
Canalis basilaris medianus (CBM) is a unique anatomical variation located in the basal occipital region of the skull, rarely encountered in head and neck radiographic imaging. The aim of the present study was to evaluate the prevalence and types of CBM using Cone Beam Computed Tomography (CBCT) scans.
Materials and Methods
CBCT (Full FOV) images of 200 patients aged between 10 to 70 years were selected for the current retrospective study following the inclusion and exclusion criteria. The image sections from the scan data were scrutinized for the presence of CBM, in addition to its classification based on the type of morphology. The presence and types of CBM were recorded based on the age and gender. The chi-square test was used to analyze the presence and types of CBM with regard to gender and age group.
Results
The overall prevalence of CBM was estimated as 9.5%. CBM was present in 13% of males and 3% of females (p = 0.021). Considering the types of CBM, the superior recess type was predominantly observed followed by the inferior recess, superior and inferior type. However, there was no significant gender-based differences noted among the types of CBM (p > 0.05). Also, there was no statistically significant difference noted in the prevalence of CBM in different age groups (p > 0.05).
Conclusion
It is necessary for maxillofacial radiologists to have a solid understanding of both normal and variant skull-base anatomy to facilitate recognition of variants such as CBM in order to recognize the associated anomalies. To our knowledge, this was the first study done which assesses the gender-based differences among the various types of CBM.
Many studies have considered the temporal patterns of reproduction of Engraulis ringens, but little attention has been given to the spatial patterns of reproduction (spawning areas), which have shown great variability in both location (geographical position) and extent (the area covered by positive stations), without a satisfactory explanation. Along the Chilean coast, the daily egg production method (DEPM) has been used for several years to estimate spawning biomass in the northern Chile E. ringens population, with 24 surveys being carried out from 1992 to 2020. The most fluctuating parameters estimated in the DEPM have been the location and extent of the spawning area and the average female weight. In the last few years the eggs were distributed near the coast, whereas in the first few years they showed a more oceanic distribution. The average female weight has fallen from 30 g in the 1990s to 11 g in the last few years. In the present study, we analysed the relationship of the location and extent of spawning areas with female size and abundancy in E. ringens from northern Chile. According to the results, periods of high abundancy of eggs are positively correlated with larger females that spawn in more oceanic zones and to the south, expanding the spatial egg distribution and increasing the egg density. By contrast, in years with low abundance of eggs, the spawning was located north and towards the coast, with a smaller spawning area and smaller female size.
The condylar canal and its associated emissary vein serve as vital landmarks during surgical interventions involving skull base surgery. The condylar canal serves to function as a bridge of communication from the intracranial to extracranial space. Variations of the condylar canal are extremely prevalent and can present as either bilateral, unilateral, or completely absent. Anatomical variations of the condylar canal pose as a potential risk to surgeons and radiologist during diagnosis as it could be misinterpreted for a glomus jugular tumor and require surgical intervention when one is not needed. Few literature reviews have articulated the condylar canal and its associated emissary vein through extensive imaging. This present paper aims to further the knowledge of anatomical variations and surgical anatomy involving the condylar canal through high-quality computed tomography (CT) images with cadaveric and dry bone specimens that have been injected with latex to highlight emissary veins arising from the condylar canal.
Purpose
This study determined the prevalence of fossa navicularis magna (FNM), canalis basilaris medianus (CBM), and craniopharyngeal canal (CPC), the size of FNMs, and types of CBM using 3D computed tomography (CT) images.
Methods
A total of 1059 3D images [649 cone beam computed tomography (CBCT) and 410 CT] were evaluated in this study. The prevalence of FNM, CBM, and CPC, length, width, and depth of FNM, and type of CBM were assessed.
Results
Overall, FNM was identified in 7.6%, CPC in 0.3%, and CBM in 2.5% of the study group. Type 2 (0.1%) and Type 6 (0.1%) are the least common CBM types. There was no significant difference between genders for depth and width measurements (p > 0.05), however, the length of FNM was significantly higher in males than females in CBCT images (p = 0.02).
Conclusion
FNM, CBM, and CPC are rare anatomical variants of clivus. However, they can facilitate spread of infection to the skull base or vice-versa. These types of anatomical variations should be known by radiologists to avoid unnecessary diagnosis and treatment procedures and to distinguish anatomic variations from pathological conditions.
The temporal bone is one of the more complex structures at the skull base that houses the hearing and vestibular organs, numerous nerves, and vessels. A host of inflammatory and neoplastic processes can occur within the temporal bone that often necessitate permanent and frozen section pathologic examination. A number of simple to complex surgical procedures are used to manage temporal bone pathology. This chapter will provide a brief overview of normal temporal bone anatomy, common surgical approaches, normal histology, and indications for pathologic examination.
The fossa navicularis is an anatomical variant of the skull base thought to be a rare finding. It represents a bony depression in the skull base. The authors here report the case of a fossa navicularis magna in a 9-year-old female who had been treated for recurrent episodes of meningitis.
A literature review was also done to highlight the unique features and clinical importance of this distinctive radiological skull base finding. The literature search covered papers from the 19th century up to 2018. Earlier authors described “fossa navicularis” as a very rare skull base finding. So far, only three cases of fossa navicularis with associated clival or intracranial infection have been reported in the literature. This is the fourth reported case, and the defect was closed endoscopically via a transnasal route. This morphological skull base anomaly should be considered in the differential diagnoses for an unexplained skull base infective pathology.
Skull base surgeons should be aware of the existence of the fossa navicularis because of its clinical importance in rendering a prompt diagnosis and appropriate treatment.
Foramen tympanicum (FT), or foramen of Huschke, describes an uncommon anatomicvariant of a persistent bony defect connecting the external acoustic meatus to the temporomandibular joint (TMJ). Although rare, it can be associated with significant complications, such as TMJ herniation, salivary gland fistula, infectious or tumoral spread between the external acoustic meatus and the TMJ, or result in inadvertent ear injury during TMJ arthroscopy. To the best of our knowledge, this is the first case report of a symptomatic FT with a full description of computed tomography and magnetic resonance imaging findings. Surgical exploration confirmed the presence of FT with TMJ herniation with subsequent successful closure of the defect obtained.
The foramen of Huschke, or foramen tympanicum, is a developmental defect in the bony part of the external auditory canal (EAC) due to a defect in ossification of normal bone in the first 5 years of life. Seen in the anteroinferior part of the EAC, it can be asymptomatic or present with salivary discharge into the EAC during mastication or as soft tissue swelling in the EAC in the absence of any inflammation, tumor, or trauma. We present a case of a man who presented with herniation of soft tissues of the temporomandibular joint into the EAC through a persistent foramen tympanicum.
Introduction Benign paroxysmal positional vertigo is a generally benign condition that responds to repositioning maneuvers and frequently resolves spontaneously. However, for some patients it can become a disabling condition in which surgery must be considered. Two different surgical techniques exist, singular neurectomy and posterior semicircular canal occlusion.
Objective The objective of this study is to review the current status of singular nerve section and posterior semicircular canal occlusion as treatments for intractable benign paroxysmal positional vertigo, and to determine if there are published data available that favors one over the other.
Data Sources MEDLINE and OLDMEDLINE databases of the National Library of Medicine.
Data Synthesis Four studies regarding singular neurectomy and 14 reports on semicircular canal occlusion were analyzed. Both techniques are reported to provide similar symptomatic benefit, with low risk of hearing loss and balance impairment. However, anatomical and clinical studies of singular neurectomy show it to be a more challenging technique, and considering that it is indicated in a very small number of cases, it may be difficult to master.
Conclusions Both singular neurectomy and semicircular canal occlusion can be safe and effective in those few patients that require surgery for intractable positional vertigo. Although semicircular canal occlusion requires a postauricular transmastoid approach, it is ultimately easier to learn and perform adequately, and thus may be considered the best alternative.
Identification of the cause of recurrent meningitis may pose a diagnostic challenge. Evaluation of a patient with recurrent meningitis calls for meticulous review of skull base structures by cross sectional imaging to exclude any underlying anatomical abnormality. Our case highlights the importance of excluding persistent craniopharyngeal duct, a rare but treatable cause of recurrent meningitis. The isolation of Streptococcus pneumoniae in recurrent meningitis may be a clue to the presence of a skull base abnormality. Craniopharyngeal canals have been classified depending on their qualitative and quantitative imaging features. Such imaging based classification is important for identification of patients with associated potential pituitary involvement and also for appropriate surgical planning. Controversy exists as to the approach to surgical treatment of craniopahryngeal duct. The persistent craniopahryngeal duct in our patient was successfully treated by an endoscopic transsphenoidal approach.
The tympanic (Jacobson’s) nerve is a useful anatomi- cal structure in the middle ear with both practical and physiological functions extending beyond its origin. The paper reviews its clinical anatomy in adults and its surgical significance. English language articles from 5 major databases and Google scholar search engine were used to identify papers outlining the anatomy of the tympanic nerve, associated pathology and surgical relevance. In the majority of cases the tympanic nerve arises from the inferior ganglion of the glossopharyn- geal nerve traversing through the tympanic canaliculus into the middle ear. On the promontory it coalesces with sympathetic fibres from the carotid chain forming the tympanic plexus which has individual variability. Functionally, as well as giving off parasympathetic fibres to the parotid gland via the lesser petrosal nerve, it is a useful anatomical landmark for cochlear implantation. The surgical importance of the tympanic nerve is not only restricted to middle ear surgery; it also extends to salivary gland disorders. The tympanic nerve remains clinically relevant to the modern otolaryngologist and as such a detailed understanding of its anatomy is crucial.
The foramen Vesalius is located within bony plate between the foramen ovale and the foramen rotundum in the floor of middle cranial fossa. This foramen allows passage of emissary veins which communicate cavernous sinus and pterygoid plexus of veins.
To study the morphological and morphometric variations of foramen Vesalius in dry adult human skulls.
One hundred and fifty dry adult human skulls were studied for variations in size, shape, presence/absence and any duplication/multiplication of the foramen Vesalius. After collecting data, appropriate statistical analysis was done.
The mean maximum dimension of foramen Vesalius was 0.98±0.67 mm on right side and 1.12±0.73 mm on left side. Foramen Vesalius was present in 90 (60%) skulls out of 150 observed. The incidence was 41(27.33%) on right side and 49 (32.67%) on left side. Foramen Vesalius was present unilaterally in 32 (35.56%) and bilaterally in 29 (32.23%) out of 90 skulls. Duplication of this foramen was observed in two skulls (one right side and one on left side). Foramen Vesalius was round in 72%, oval in 24% and irregular in 4% of total foramina present.
Foramen Vesalius was present in 60% of total skulls studied. The foramen showed variations in incidence and shapes, while there was no statistically significant difference in the maximum dimension between foramen Vesalius on right and left side. There could be some developmental reasons to explain these variations. The findings of this study could be important to anatomists and also equally essential for clinicians who approach middle cranial cavity for various procedures.
The identification of mastoidal emissary veins is of importance in the neurosurgical practice to diagnose abnormal and normal structures. In the present study, the objectives were to estimate the prevalence rate of mastoidal emissary foramina in the temporal bones of the adult skull and to study their number and morphology. The present study included 48 adult human skulls which were obtained from the gross anatomy laboratory of our institution. The mastoid parts of 96 temporal bones were macroscopically observed for the prevalence, number and morphology of the emissary foramina. It is observed that, the mastoidal emissary foramen was present in 88 temporal bones (91.7%) of our specimens. The foramen was observed single in 60 temporal bones (62.5%), double in 22 bones (22.9%), and triple in 6 temporal bones (6.2%). The mastoidal emissary foramen was absent in 8 (8.3%) temporal bones. The foramen was bilaterally absent in 3 (3.1%) skulls. It was unilaterally absent in 2 (2.1%) skulls and both were on the left side. The mastoidal emissary vein is prevalent in a large number (91.7%) of cases. It was observed that the accessory mastoidal emissary foramina were present in 29.1% of cases. Recognition of the mastoid emissary veins and accessory mastoid emissary veins during the otologic surgery is critical to avoid the significant bleeding. In the neurosurgical practice, the knowledge is important due to variability in the number of mastoidal emissary veins and their connection to the venous sinuses.
The paradigm for the management of epistaxis, specifically posterior epistaxis, has undergone significant changes in the recent past. Recent prospective and retrospective data has shown that the endonasal surgical management of posterior epistaxis is superior to posterior nasal packing and angiography/embolization with regards to various factors including pain, cost-effectiveness, risk and overall control of bleeding. Endonasal endoscopic surgical techniques for posterior epistaxis include direct cauterization and transnasal endoscopic sphenopalatine/ posterior nasal artery ligation or cauterization with or without control of the anterior ethmoidal artery. Despite the evidence provided by the current literature, a universal treatment protocol has not yet been established. This review article provides an up-to-date assessment of the available literature, and presents a structured paradigm for the management of posterior epistaxis.
A bony defect of the external auditory canal (EAC) and herniation of the temporomandibular joint (TMJ) can be caused by tumorous conditions, inflammation, trauma, and otologic procedures. Spontaneous TMJ herniation into the EAC can be caused by a congenital bony defect known as patent Huschke's foramen, which is a very rare condition. In our case, an objective clicking sound was produced when the patient opened his mouth. A protruding mass was found in the anterior wall of the EAC during mouth closing, and herniation of the TMJ was confirmed with computed tomography. Therefore, we thought the clicking sound of our case could have resulted from spontaneous TMJ herniation through the patent foramen of Huschke.
PurposeTo characterize the MRI features of the petromastoid canal in children with sensorineural hearing loss (SNHL) and in normal infants.Materials and Methods
High resolution MRI examinations of 564 children who were evaluated for SNHL and brain MRI examinations of 112 infants who had normal studies were studied independently by two reviewers.ResultsIn SNHL group, visibility of the PMC decreased for right and left PMC (P < 0.001). The width of the right PMC significantly decreased as age increased (P < 0.0001). There was no relation between abnormalities of membranous labyrinth and cochlear nerve and PMC visibility in children with SNHL (p > 0.05). In the normal group, the PMC visibility decreased with increasing age (right P = 0.0001, left P = 0.001). In the normal group also, as age increased, the PMC width decreased for both PMCs (right, P = 0.0006; left, P = 0.03).Conclusion
The PMC is more frequently visualized in young children. Its visibility and width are not associated with abnormalities of membranous labyrinth and cochlear nerves. J. Magn. Reson. Imaging 2014;39:966–971. © 2013 Wiley Periodicals, Inc.
Jacobson's nerve schwannoma is a rare middle ear tumour presenting as a mass along the cochlear promontory. It can be differentiated from other masses along the promontory based on clinical findings, and computed tomography and magnetic resonance imaging features. For small-sized masses, it is possible to differentiate the various middle ear schwannomas from one another. We present the case of a 40-year-old woman with a ten-year history of left hearing loss who was diagnosed with Jacobson's nerve schwannoma.
Object:
There are several surgical techniques for reducing blood loss-open surgical and endoscopic-prior to resection of giant anterior skull base meningiomas, especially when preoperative embolization is risky or not technically feasible. The authors present examples of an institutional experience using surgical ligation of the anterior and posterior ethmoidal arteries producing persistent tumor blush in partially embolized tumors.
Methods:
The authors identified 12 patients who underwent extracranial surgical ligation of ethmoidal arteries through either a transcaruncular or a Lynch approach. Of these, 3 patients had giant olfactory groove or planum sphenoidale meningiomas. After approval from the institution privacy officer, the authors studied the medical records and imaging data of these 3 patients, with special attention to surgical technique and outcome. The variations of ethmoidal artery foramina pertaining to this surgical approach were studied using preserved human skulls from the Hamann-Todd Osteological Collection at the Museum of Natural History, Cleveland, Ohio.
Results:
The extracranial ligation was performed successfully for control of the ethmoidal arteries prior to resection of hypervascular giant anterior skull base meningiomas. The surgical anatomy and landmarks for ethmoidal arteries were reviewed in anthropology specimens and available literature with reference to described surgical techniques.
Conclusions:
Extracranial surgical ligation of anterior, and often posterior, ethmoidal arteries prior to resection of large olfactory groove or planum sphenoidale meningiomas provides a safe and feasible option for control of these vessels prior to either open or endoscopic resection of nonembolized or partially embolized tumors.
The maxillary artery is a terminal branch of the external carotid artery. Although the main maxillary artery trunk and most of its branches course within the extracranial space and supply the organs and muscles of the head and neck, other surrounding soft tissues, and the oral and rhinosinusal cavities, other branches supply the dura mater and cranial nerve and can anastomose to the internal carotid artery (ICA). Various pathologic conditions of the intracranial, head, and neck regions can involve the branches of the maxillary artery. Many of these diseases can be treated with endovascular approaches; however, there is a potential risk of complications in the brain parenchyma and cranial nerves related to the meningoneuronal arterial supply and anastomoses to the ICA. Therefore, familiarity with the functional and imaging anatomy of the maxillary artery is essential. In the past, conventional angiography has been the standard imaging technique for depicting the maxillary artery anatomy and related pathologic findings. However, recent advances in computed tomographic, magnetic resonance, and rotational angiography have further elucidated the maxillary artery anatomy by means of three-dimensional representations. Understanding the functional and imaging anatomy of the maxillary artery allows safe and successful transcatheter treatment of pathologic conditions in the maxillary artery territories.
Posterior fossa emissary veins are valveless veins that pass through cranial apertures. They participate in extracranial venous drainage of the posterior fossa dural sinuses. The mastoid emissary vein, condylar veins, occipital emissary vein, and petrosquamosal sinus are the major posterior fossa emissary veins. We believe that posterior fossa emissary veins can be detected by radiologists before surgery with a thorough understanding of their anatomy. Describing them using temporal bone computed tomography (CT), CT angiography, and cerebral magnetic resonance (MR) venography examinations results in more detailed and accurate preoperative radiological interpretation and has clinical importance. This pictorial essay reviews the anatomy of the major and clinically relevant posterior fossa emissary veins using high-resolution CT, CT angiography, and MR venography images and discusses the clinical importance of reporting these vascular variants.
The skull base anatomy is complex. Numerous vital neurovascular structures pass through multiple channels and foramina located in the base skull. With the advent of computerized tomography (CT) and magnetic resonance imaging (MRI), accurate preoperative lesion localization and evaluation of its relationship with adjacent neurovascular structures is possible. It is imperative that the radiologist and skull base surgeons are familiar with this complex anatomy for localizing the skull base lesion, reaching appropriate differential diagnosis, and deciding the optimal surgical approach. CT and MRI are complementary to each other and are often used together for the demonstration of the full disease extent. This article focuses on the radiological anatomy of the skull base and discusses few of the common pathologies affecting the skull base.
Establishing the diagnosis of morning glory disc anomaly is crucial to appropriate patient treatment. Although typically made clinically, the diagnosis is not always straightforward, especially in circumstances where physical examination is limited. The goal of this study was to define the spectrum and frequency of orbital findings in a series of patients with funduscopically-confirmed morning glory disc anomaly by using MR imaging. MR imaging demonstrated 3 findings in all patients: 1) funnel-shaped morphologic pattern of the posterior optic disc with elevation of the adjacent retinal surface; 2) abnormal tissue associated with the distal intraorbital segment of the ipsilateral optic nerve, with effacement of the regional subarachnoid spaces; and 3) discontinuity of the uveoscleral coat. These findings were not observed in any of the unaffected globes of the study patients. In summary, these consistent and characteristic findings of morning glory disc anomaly should allow for accurate differentiation from other ocular anomalies and have the potential to guide appropriate management of this patient population.
Although pulsatile tinnitus can be audible, objective demonstration of this heartbeat-synchronous sound has rarely been successful. We report a rare case of pulsatile tinnitus in a 44-yr-old female patient, which was induced by a large mastoid emissary vein (MEV) and objectively documented by Doppler sonography of the left posterior auricular region. The tinnitus was intermittent and the patient could adapt to the tinnitus without intervention on the mastoid emissary vein. These findings suggest that a single large MEV can cause pulsatile tinnitus in the absence of other vascular abnormalities, and imaging studies of the posterior fossa and Doppler ultrasonography can aid the diagnosis in such cases.
Congenital occipital dermal sinus with an underlying dermoid is a rare, benign lesion of embryological origin and may occur anywhere along the neuraxis. We present a case of a 15-year-old girl with a vermian dermoid and an occipital dermal sinus. Gross total resection of the lesion was done and post-operative period was uneventful. A detailed review of the literature is also covered.
All 377 dry skulls were examined for the occurrence and morphometry of the foramen of Vesalius (FV) both in the middle cranial fossa and at the extracranial view of the skull base. There were 25.9% and 10.9% of FV found at the extracranial view of the skull base and in the middle cranial fossa, respectively. Total patent FV were 16.1% (11.9% unilaterally and 4.2% bilaterally). Most FV were found in male and on the left side. Comparatively, FV at the extracranial view of the skull base had a larger maximum diameter. The distance between FV and the foramen ovale (FO) was as short as 2.05 ± 1.09 mm measured at the extracranial view of the skull base. In conclusion, although the existence of FV is inconstant, its occurrence could not be negligible. The proximity of FV to FO should remind neurosurgeons to be cautious when performing the surgical approach through FO.
Sternberg's (lateral craniopharyngeal) canal was originally described in anatomic studies as a membranous space in the lateral wall of the sphenoid sinus. The canal has been etiologically associated with lateral sphenoid sinus "spontaneous" cerebrospinal fluid (CSF) leaks. A patent Sternberg's canal has been reported in up to 4% of adults, and persistent vestiges have been reported in up to 30%. However, no modern studies analyzing high-resolution CT scans have been published.
A consecutive analysis of 1000 high-resolution CT scans of sphenoid bones was performed. Scans were analyzed for a lateral recess, bony defects, arachnoid pits, and holes possibly representing Sternberg's canal. Data were compared with a case series of lateral sphenoid CSF leaks.
Average patient age was 38.7 years (10-92 years). A sphenoid lateral recess was present in 35.3% (17.4% bilateral) of cases. Arachnoid pits were present on the floor of the middle cranial fossa in 23.4% of cases. Seven skull base defects were identified. Only one traveling medial to V2 resembled the description of Sternberg's canal. In contrast, a case series of 25 patients with lateral sphenoid sinus CSF leaks all had a lateral recess, defects, and arachnoid pits lateral to V2 (p < 0.00001).
Sternberg's canal as historically defined is not nearly as prevalent as previously reported. Furthermore, the presence of arachnoid pits in all sphenoid CSF leaks and the predominant leak location lateral to the sites of fusion of ossification centers suggests that the leaks are acquired. Contributing factors may include arachnoid pits/weaknesses in the skull base and intracranial hypertension.
MR was helpful in demonstrating the spatial relationship between a dermoid cyst in the fourth ventricle and an occipital dermal sinus. T1-weighted images clearly showed the mixed hypointense mass in the fourth ventricle and above the vermis, which appeared to be connected to an occipital dermal dimple.
Background and purpose:
Necrotizing external otitis is a serious complication of external otitis with different spreading patterns. A persistent foramen of Huschke is a dehiscence located antero-inferior in the osseous external ear canal and posterior-medial to the temporomandibular joint. This dehiscence can facilitate extension of infection in an anterior pattern next to classic spread along the fissures of Santorini. The aim of this study was to define the prevalence and size of a persistent foramen of Huschke in patients with necrotizing external otitis.
Materials and methods:
We retrospectively examined 78 CT temporal bone studies (39 patients with necrotizing external otitis, 39 control subjects). The side and presence of the foramen were noted, and its prevalence was calculated. The maximal width of the foramen of Huschke was measured in the axial plane and classified as subtle, mild, moderate, or extensive.
Results:
A persistent foramen of Huschke was present in 21 patients (26 ears) and 7 control subjects (9 ears). Prevalence was 50% (20/40) and 11.5% (9/78) in affected ears of patients with necrotizing external otitis and control subjects, respectively. Almost all affected ears showed an anterior distribution pattern of necrotizing external otitis. The extensive dehiscence was most common in affected ears.
Conclusions:
An anterior necrotizing external otitis spreading pattern is associated with the presence and increased size of a persistent foramen of Huschke. These findings facilitate the theory that a persistent foramen of Huschke is an additional risk factor the development of necrotizing external otitis.
The skull base is a complex bony and soft tissue interface that is divided anatomically into compartments. This article will focus specifically on the central skull base, which has a complex embryologic development and anatomy. Multiple entities from notochord remnants, neoplasm, infection, and other abnormalities may occur, and imaging is critical for depicting skull base pathology.
Although functional endoscopic sinus surgery is an effective means of treating patients with recurrent and refractory sinusitis, the procedure is not without risk of serious surgical complications. Preoperative computed tomography (CT) affords radiologists the opportunity to prospectively identify anatomic variants that predispose patients to major surgical complications; however, these critical variants are not consistently evaluated or documented on preoperative imaging reports. The purpose of this review is to illustrate important anatomic variants and landmarks on the preoperative sinus CT with a focus on those that predispose patients to surgical complications. These critical variants and landmarks can be quickly recalled and incorporated into the preoperative imaging report through the use of the mnemonic "CLOSE": Cribriform plate, Lamina papyracea, Onodi cell, Sphenoid sinus pneumatization, and (anterior) Ethmoidal artery. This approach will greatly enhance the value of the preoperative imaging report for referring otolaryngologists and help reduce the risk of surgical complications. (©) RSNA, 2016 Online supplemental material is available for this article.
Objective: To study the positions, features and sectional anatomy of the palatovaginal canal and vomerovaginal canal, comparing with CT and MRI findings. Methods: The palatovaginal canals in 104 sides and vomerovaginal canals in 60 sides of dry skulls were observed. Three adult cephalic specimens were sliced into celloidin contiguous sections on coronal plane(0.5 mm in thickness) and the results were correlated with the CT studies of 11 patients and MR imaging of a cephalic specimen. Results: In dry skulls, the palatovaginal canal displayed as complete canal in 79.8% of the cases, while appeared as groof in 15.4%. There was neither significant canal nor groof in 4.8%. The vomerovaginal canal demonstrated as complete canal in 36.7% of the speciments, while appeared as groof in 33.3% This canal was communicated with the lateral palatovaginal canal in 15% and it was not detected in 15%. Four typical slices of the celloidin and 3 plane of CT and 3 plane of MRI were selected and the key structures were described. Conclusion: The palatov aginal canal and vomerovaginal canal can be well depicted on coronal plane.
Background:
Occipital dermal sinus, usually associated with dermoid cyst, is a rare entity; it results from the persistence of an abnormal embryonal communication between the skin and the intradural space. Its main complication is intracranial infection.
Case description:
This 2-year-old girl was hospitalized for meningitis. Neuroradiological studies revealed a cystic mass of the posterior fossa communicating with the skin and hydrocephalus. The diagnosis of dermoid cyst associated with dermal sinus was established at surgery. The patient was treated with radical excision of both the occipital cyst and the dermal sinus associated with systemic antibiotic therapy. She had a good outcome.
Conclusion:
Posterior fossa dermoid cyst should be considered in all children with chronic occipital skin lesion, especially a dermal sinus. We emphasize the importance of early neurosurgical treatment of dermoid cysts to prevent the development of severe complications.
This study is to palatovaginal canal and vomerovaginal canal identify by computed tomography (CT) transverse imaging and are often mislabeled by investigators. We used a probe guide method in skull specimens to establish the CT imaging features of the two canals. We also used endoscopy to look deeply into the inside structure of them. Finally, CT images of patients were used to confirm our findings. Based on our results using 20 skull specimens and 70 patients, we established a simple method that can be used to identify the two canals on CT transverse imaging. In the transverse images of skull specimens and of patients, the frequency of simultaneous observation of the two canals was 72.5% and 70.71%. We also identified several mislabeled images of the palatovaginal and vomerovaginal canals in published papers. In summary, we found that the two canals could be observed and distinguished by transverse CT imaging. Furthermore, we established a method that could distinguish them. In conclusion, our findings will have a great impact not only on the accurate identification of the pterygoid canals but also on the early detection of tumor metastasis and palatine artery embolization.
The mastoid emissary vein (MEV) is an anatomical structure with limited description in the literature and its importance is even less recognized in the plastic surgical field. Investigations in its anatomy and physiology have described its anthropological significance in transition to bipedalism and preferential intracranial venous flow into the vertebral plexus in the upright man.
Inadvertant injury of vessels of this size pose a significant problem due not only to difficulty with haemostasis but also from their bidirectional flow and close proximity to the sigmoid sinus where cases of thromboembolism have been described. Recognition of this common anatomical structure and how to manage bleeding from the vessel it is important for the surgeon operating in this area and even more so for the craniofacial surgeon who operates on complex craniosynostotic patients where the MEV may be the sole dominant drainage pathway of the brain.
We conducted a study on 106 cadaveric dry skull specimens looking at the incidence, position and caliber of mastoid emissary foramina. 83.7% of skulls were found to have at least one foramen with a mean diameter of 1.64 mm and the largest specimen measuring 7 mm.
Background and purpose:
The craniopharyngeal canal is a rare, well-corticated defect through the midline of the sphenoid bone from the sellar floor to the anterosuperior nasopharyngeal roof. We reviewed a series of craniopharyngeal canals to determine a system of classification that might better our understanding of this entity, highlight the range of associated pathologic conditions, and optimize patient treatment.
Materials and methods:
Available MR imaging, CT, and clinical data (from 1989-2013) of 29 patients (10 female, 15 male, 4 unknown; median age, 4 years; age range, 1 day-65 years) with craniopharyngeal canals were retrospectively examined. Qualitative assessment included orthotopic or ectopic adenohypophysis and the presence of a tumor and/or cephalocele. The midpoint anteroposterior diameter was measured. Clinical and imaging data were evaluated for pituitary dysfunction and accompanying anomalies.
Results:
Craniopharyngeal canals were qualitatively separated into 3 types: incidental canals (type 1); canals with ectopic adenohypophysis (type 2); and canals containing cephaloceles (type 3A), tumors (type 3B), or both (type 3C), including pituitary adenoma, craniopharyngioma, dermoid, teratoma, and glioma. Quantitative evaluation showed a significant difference (P < .0001) in the anteroposterior diameters of type 1 canals (median, 0.8; range, 0.7-1.1 mm), type 2 canals (median, 3.9, range, 3.5-4.4 mm), and type 3 canals (median, 9.0; range, 5.9-31.0 mm) imparting small, medium, and large descriptors. Canals with cephaloceles all contained an ectopic adenohypophysis. The craniopharyngeal canals were associated with pituitary dysfunction (6/29) and congenital anomalies (8/29).
Conclusions:
Accurate diagnosis and classification of craniopharyngeal canals are valuable to characterize lesions requiring surgery, identify patients with potential pituitary dysfunction, and avoid iatrogenic hypopituitarism or CSF leak during surgical resection of nasopharyngeal masses.
Several inconstant skull base foramina can be observed on multi-detector-row computed tomographic studies. These include the meningo-orbital foramen, foramen of Vesalius, canaliculus innominatus, palatovaginal canal, persistent craniopharyngeal canal, transsphenoidal canal, canalis basilaris medianus, and fossa navicularis. Although many of these foramina are simply incidental findings, there may be associated anomalies and important clinical implications. The multi-detector-row computed tomographic features of variant skull base foramina are depicted and discussed in this article.
Objective:
The objective of this article is to discuss and illustrate commonly visualized fissures and sutures in the temporal bone. This topic is important because a thorough knowledge of normal anatomy is necessary to avoid misinterpretation as fractures.
Conclusion:
Small normal anatomic fissures are now routinely visualized with the increasing use of MDCT in trauma patients. An awareness of these structures is required by radiologists interpreting studies with fine temporal bone slices to prevent erroneous interpretation.
An aberrant subarcuate artery and its related canal are rare. The presence of this variation has a surgical significance, that is, risk of hemorrhage, if accidentally nicked. It is therefore important to be aware of this entity, and its relative anatomy, to avoid any untoward complication. We present a case of a 29-year-old man who presented with hearing loss after trauma. High-resolution computed tomographic scan of the temporal bone demonstrated an enlarged subarcuate canal.
Hyrtl's fissure is a cleft that is present in the developing fetal petrous temporal bone and extends from the area inferior to the round window to the meninges of the posterior fossa. Persistent Hyrtl's fissure, due to incomplete ossification, is considered a rare temporal bone malformation, and is a known cause of perilabyrinthine cerebrospinal fluid fistula. Very few cases are reported as being at risk of complication of cochlear implant surgery. Here we report the case of an 8-year-old boy with misplacement of an electrode array in Hyrtl's fissure. The diagnosis was made postoperatively, since cochlear implant failure was suspected from non-auditory responses. Computed tomography (CT) revealed the extracochlear location of the electrode array. We emphasize the role of presurgical imaging CT and magnetic resonance imaging in detecting temporal bone abnormalities, and we discuss the value of intraoperative auditory nerve response telemetry and postoperative radiological evaluation in diagnosing cochlear implant misplacement.
The fossa navicularis is a notch-like bone defect in the basiocciput that has been hitherto considered as an anatomical variant of the clivus and not previously described as a potential source of clival or skull base pathology. We report the imaging findings in a 5-year-old child who presented acutely with a retropharyngeal abscess and osteomyelitis of the clivus. Imaging after treatment revealed a "notch-like" defect in the anterior clivus consistent with a fossa navicularis. Based on these appearances, we postulate that the lymphoid tissue of the pharyngeal tonsil residing in the fossa navicularis served as a route through which infection spread and subsequently developed into clival osteomyelitis, which is a rare diagnosis. This case is unique, and we believe that the presence of this variant in young children may be important and is not merely an anatomical curiosity.
Four locations for congenital cerebrospinal fluid fistula in the region of a normal labyrinth are reviewed. A congenital leak may occur through the petromastoid canal, a wide cochlear aqueduct, Hyrtl's fissure, or the facial canal. A fistula through the initial segment of the fallopian canal was successfully repaired in a two-year-old boy who had three episodes of meningitis following otitis media. Knowledge of these four sites of congenital defects provides a guideline for the surgeon in the identification and repair of cerebrospinal fluid leaks in the region of the labyrinth.
A complete otoscopic examination should be performed in all patients seeking treatment of temporomandibular disorders. The presence of a bulge in the external auditory meatus that disappears with mouth opening may suggest the persistence of the foramen of Huschke. The clinician should rule out the presence or history of infection, trauma, or neoplasm before ascribing the etiology of a defect to a developmental aberration.
The significance and cause of ventriculomegaly in achondroplasia was investigated in five achondroplastic children. The intraventricular pressure (IVP) was monitored over 24 hours, followed by intraventricular injection of radionuclide alone or in combination with water-soluble contrast material. The IVP was elevated and the reabsorption of cerebrospinal fluid (CSF) into the sagittal sinus was slow in all cases, but there was no obstruction to CSF flow. The spinal subarachnoid space was well seen in all patients. Jugular venograms with pressure monitoring were obtained in four patients (bilaterally in one). These studies confirmed a narrow jugular foramen in all patients with a significant venous pressure gradient (3 to 10 mm Hg) obtained while the catheter was being pulled back from the sigmoid sinus through the foramen. A second gradient was found in the jugular vein in two patients at the level of the upper thoracic aperture. This gradient was 6 and 14 mm Hg, respectively. Identical venograms and monitoring of the venous pressure in a control group showed no pressure gradients across the jugular foramen and smaller gradients (2 to 5 mm Hg) across the thoracic inlet.
It is concluded from these studies that ventriculomegaly in achondroplastic children represents hydrocephalus, which is likely secondary to raised intracranial venous pressure due to hemodynamically significant stenosis of the jugular foramen and, in some cases, the jugular vein in the thoracic aperture.
Two children are described in whom a deep recess in the inferior surface of the basiocciput was discovered as an incidental finding during a CT scan of the skull. The finding is interpreted as an incomplete form of canalis basilaris medianus and is possibly related to the cephalic end of the notochordal canal. It is considered to be an anatomic variant of no clinical significance and may be differentiated from a complete canal through the basiocciput only by sagittal polytome tomography or by a CT scan of the area with reformatted images.
The foramen of Vesalius is a small, variable but consistently symmetrical structure located anteromedial to the foramen ovale and lateral to the foramen rotundum and vidian canal. It transmits an emissary vein through which the cavernous sinus and pterygoid plexus communicate. Fifty high-resolution CT scans of the skull base and two three-dimensional (Cemax) reconstructions were reviewed to determine criteria for defining the normal appearance of the foramen of Vesalius. Three normal types were classified: (1) a well-formed foramen, 1-2 mm in size (n = 32); (2) lack of visualization of the foramen (n = 11); and (3) partial assimilation of the foramen with the foramen ovale (n = 7). The foramen was remarkably symmetric in a large number of cases (n = 48). Asymmetry signified abnormality in four of the six cases. Abnormal causes of asymmetry included invasion by nasopharyngeal melanoma, angiofibroma, carotid cavernous fistula with drainage through the emissary vein, and neurofibromatosis. Thus, for these usually symmetric foramina of Vesalius, asymmetry is more likely the result of a pathologic process than a normal variant.
A vertical conduit in the basisphenoid extending from the floor of the sella to the undersurface of this bone was observed in two children. There was no associated nasopharyngeal mass. A review of the literature on this defect and related subjects suggests a close relation between this lesion and transsphenoidal meningoencephalocele.
To assess the prevalence and appearance of the posterior condylar canal using high-resolution CT.
One hundred twenty-three high-resolution temporal bone CT examinations were retrospectively reviewed for the presence or absence of the posterior condylar canal. Thirty-four gross skulls were also examined.
The posterior condylar canal was identified on CT bilaterally in 31% of the final study group and unilaterally in 50%. On gross specimens, this structure was identified in 55.9% bilaterally and 17.6% unilaterally. The posterior condylar canal, when present, is readily identifiable in a predictable location. The imaging appearance of this structure is dependent on its relationship to the angle of scanning.
The posterior condylar canal is among the largest emissary foramina in the human skull. Recognition of this structure and its role as an alternative source of venous drainage from the brain will help avoid misinterpretation during CT examination.
To evaluate by means of high-resolution CT the anatomic variations of the middle cranial fossa foramen.
We examined 123 CT studies of the temporal bone in patients with no evidence of disease that might alter foraminal anatomy. A checklist of known variants and suspected structures was used as each case was systematically examined for the presence or absence of these foramina; variations in size, shape, and location; and relationship of structures to each other. Inclusion criteria were established to eliminate error.
The foramen rotundum had a constant appearance. We identified the inferior rotundal canal in 16% of patients and the lateral rotundal canal in 8%. The foramen of Vesalius was present, at least unilaterally, in 80% of our cases. Asymmetry of the foramen of Vesalius did not indicate disease in our patient group. We did not find an inverse relationship between the size of the foramen of Vesalius and that of the ipsilateral foramen ovale. We found variations in the size and shape of the foramen ovale and its confluence with the foramen spinosum (n = 2) and the foramen of Vesalius (n = 8). We did not find an inverse relationship between the size of the foramen ovale and that of the foramen spinosum. The canaliculus innominatus for the lesser superficial petrosal nerve was identified in 16.3% of our patients. Variations of the foramen spinosum that we found include a medial bony defect (26.8%) and absence (3.2%).
Although it is unlikely that well-formed foramen will be misinterpreted as diseased, it is nonetheless important to recognize foraminal variants and associated neurovascular anatomy.
Our study was aimed to examine the anatomic relationships of the tympanic branch of the glossopharyngeal nerve (GPN), namely the Jacobson's nerve (JN). The JN is the first branch of the GPN after having passed the jugular foramen. It contributes to the tympanic plexus on the promontory. It transmits secretory innervation to the parotid gland. Its possible role in the regulation of the middle ear pressure has also been hypothesized in terms of animal studies. Using microdissection techniques and high-resolution computed tomography (HRCT) scanning, the anatomic relationships and course of the JN were examined in eight formalin-preserved cadavers (16 sides). A morphometric analysis related to the JN was also performed both in the 16 cadavers and 40 dry-skull specimens. The JN emerged from the inferior ganglion of the GPN in all specimens. The mean distance between the ganglion and the genu of the GPN was 11.3 mm. The inferior 2/3 of the tympanic canal (TC) followed a vertical course, and then it ran anteromedially with an angle of 160 degrees to 170 degrees. The mean length of the TC was 9.5 mm. The TC was well-defined in all axial HRCT scans. In 2 cases the JN was entirely encased in a bony canal in the middle ear. A double JN was observed in one case. This study gives an additional information regarding the anatomy of the JN.