CT scan in coronal plane shows a large lesion 

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... In the osteomeatal complex (OMC) pattern, uncinatectomy with possible maxillary antrostomy and ethmoidectomy are the standard treatment (Figure 11). For frontal recess inflammatory pattern, external frontoethmoidectomy and FESS techniques to relieve the obstruction can be used. For sphenoethmoidal recess pattern, the aim is to enlarge the sphenoid ostium and establish drainage. Techniques include external approaches but endoscopic surgery with possible image guidance is used in specialist centres. For sinonasal polyposis pattern, surgical options include endoscopic polypectomy, FESS or sphenoethmoidectomy [24–26]. In patients with recurrent symptoms post surgery, imaging plays a role in assessing the extent of FESS, detecting complications and demonstrating residual patterns of disease. Where relevant, the radiologist should focus on the patency of the inferior frontal sinus drainage pathway, including lateralization of the middle turbinate and persisting agger nasi cells. The complete- ness of uncinatectomy should be assessed and particularly whether it has been performed too far posteriorly. The extent of ethmoidectomy and any post-operative synechiae obstructing sinus drainage should be recorded. Persistent sinus opacification may also result from viscous secretions. When repeat FESS is considered, there should also be careful examination of the integrity of the middle turbinate attachment to the anterior skull base (as there may be dehiscence post-turbinatectomy) and whether there is any defect within the lamina papyracea. Clearly there is role for imaging if there are overt complications such as cerebrospinal fluid (CSF) leak, orbital injury or haemorrhage. There are various different types of fungal infection. This is mainly classified as non-invasive and invasive forms. Non-invasive forms include mycetoma and allergic fungal sinusitis. Mycetoma or a fungus ball usually affects a single sinus and it demonstrates a focal lesion with areas of high density and possible calcification. Calcification associated with fungal infection is reported to be more frequently central and punctate as opposed to curvilinear and peripheral calcifications associated with chronic non-fungal secretions (Figure 12). On MRI it demonstrates low signal on T 1 but can be heterogeneous and low signal on T 2 . Allergic fungal sinusitis characteristically demonstrates multiple sinus opacification with hyperdense material on CT and sinus expansion (Figure 13). There is often a preserved rim of hypodense mucosa. Benign bony remodelling, resorption and erosion into adjacent structures can be seen. It is commonly associated with sinonasal polyposis. In invasive forms, there is extension outside the sinus lumen with involvement of the blood vessels, bone erosion and possible orbital and intracranial extension [27, 28]. It usually, but not exclusively, occurs in diabetics and other immunocompromised patients. Three invasive forms were proposed by deShazo: granulomatous, acute fulminant and chronic invasive [29]. CT findings are non-specific but typically show sinus opacification with bony erosion and soft tissue infiltration. Systemic diseases can involve the nasal cavity and paranasal sinuses. The imaging features of Wegener’s granulomatosis are initially non-specific but later on, there is typical sinonasal mass with septal perforation and non-septal bone erosion (Figure 14). The lateral nasal wall can be involved. There may be extension through the hard palate and to the orbit, deep facial spaces, nasopharynx and the skull base. The turbinates often appear truncated and shortened. In the chronic phase, the sinus walls often become thickened and a double cortical line with central marrow can be seen. The imaging differential diagnoses include sarcoidosis, cocaine and other inhaled irritants and lymphoma. Rarer causes of granulomatous infection include leprosy, syphilis and tuberculosis. Nasal tubes result in impairment of sinonasal drainage. This results in a diagnostic dilemma in a septic patient in whom other sources of sepsis have been excluded. CT or MRI is not diagnostic and sinus aspiration may be required. Retention cysts and solitary polyps are usually asymptomatic and found incidentally and are regarded as complications of inflammatory sinusitis [30, 31]. Retention cysts are common, particularly in the maxillary sinuses, and are of little significance unless they are causing obstruction to the mucociliary clearance [32, 33]. Sporadic polyps are also commonly asymptomatic and found incidentally. On imaging, these retention cysts and polyps appear as soft tissue masses with a smooth convex border. Desiccated polyps may demonstrate increased CT density. The signal intensity on MRI is dependent on the water and protein content. When an inflammatory polyp arises from the maxillary antrum and herniates through a major or accessory ostium into the nasal cavity and to the postnasal space, this is termed an antrochoanal polyp (Figure 15). On imaging, a large dumbbell shaped low density mass with widening of the maxillary ostium extending to the nasal cavity is characteristic [34, 35]. Nasochoanal, ethmochoanal and sphenochoanal polyps are rare [36, 37]. The sinonasal structures maybe expanded by polypoid masses and obstructed secretions and there is benign bone remodelling or erosion (Figure 16). Aggressive polyposis can extend into adjacent structures. The ethmoid sinus walls often become thin and can be barely visible. The maxillary infundibulum and ostium is widened if the polyps extend from the maxillary sinuses. Concurrent fungal infection is common. With an obstructed sinus ostium from trauma, previous surgery, polyps or chronic rhinosinusitis, an opacified expanded sinus or mucocoele can result. The sinus shows benign bony remodelling presumably from pressure erosion. The frontal sinuses are most commonly affected followed by the ethmoid and maxillary sinuses. If there is superimposed infection this is called a pyocoele. On CT, a low density airless sinus with smooth bony wall expansion is diagnostic [33]. On MRI the signal intensity depends on the water and proteinaceous content (Figure 17). There may be a thin rim of enhancement as opposed to an expansile tumour which will demonstrate internal enhancement. Mimics of inflammatory disease should also be considered [8]. In unilateral sinus opacification, particularly in the OMC, a middle meatal mass needs to be excluded and direct inspection of the middle meatus should be suggested. Odontogenic origin of infection can extend to the maxillary sinus and cause an OMC pattern of disease. With nasal septum pathology and bilateral advanced disease, a systemic cause should be considered. The pattern of bone involvement may be helpful in formulating a differential diagnosis. Bony sclerosis is usually associated with a chronic relapsing process (or previous surgery) and this is typically infective. A destructive pattern of bony involvement is rarely seen with inflammatory conditions such as fungal or granulomatous infection and is usually seen with carcinoma (Figure 18a,b), metastases, some sarcomas and some lymphomas. This should be distinguished from the pressure deossification at the advancing edge of an expansile slower growing lesion which will typically demonstrate some bony remodelling at its margins. This pattern is found with inflammatory lesions such as mucoceles and polyps but may be seen with slower growing tumours such as melanomas, plasmocytomas and slower growing sarcomas (Figure 18c). If a bony defect is seen in the anterior skull base adjacent to a lesion, then a cephalocele should also be excluded (Figure 19). The presence of calcification usually signifies a chronic inflammatory process (Figure 12) particularly if more discrete. However, if present within a tumour, it is suggestive of particular neoplasms such as chondrosarcoma or olfactory neuroblastoma. Choanal atresia is the most common congenital abnormality of the nasal cavity. It can be unilateral (more common) or bilateral, bony (more common) or membranous [38]. In bilateral disease, it causes respiratory distress in the newborn. CT would show narrowing of the posterior nasal cavity at the level of the choana with obstruction from a membranous or osseous cause. There is often thickening of the vomer. Nasolacrimal duct dacrocystocoeles represent a cystic dilatation of the nasolacrimal apparatus secondary to obstruction of the nasolacrimal duct [39]. Bilateral medial canthal cystic masses are characteristic. Piriform aperture stenosis is a rare condition in which there is bony narrowing of the anterior nasal cavity. It is associated with holoprosencephaly or other anomalies. There is often a central mega-incisor [40]. Cephaloceles are congenital herniations of neural tissue (brain, CSF, meninges) through a mesodermal defect in the anterior skull. There are three main types – frontonasal, nasoethmoidal and naso-orbital cephalocoeles [41]. A defective anterior neuropore may also result in a dermal sinus tract, dermoid or nasal glioma (an extracranial rest of glial tissue rather than a neoplasm) in the frontonasal region. A frontonasal dermoid maybe associated with CT evidence of a bifid crista galli with a large foramen caecum and a sinus or cyst in the frontonasal region [42] (Figure 20). MRI is used to identify any intracranial extension of a dermoid which may be purely extradural or extend between the leaves of the falx. A wide variety of neoplasms, both benign and malignant, may arise in the sinonasal cavity. They are generally rare, particularly relative to ubiquitous inflammatory disease. The imaging appearances of the major categories will be discussed. CT and MRI are often complementary in the staging of these tumours, with CT being more sensitive to bone changes and MRI providing superior soft tissue contrast. The morphology of the tumour, enhancement pattern and pattern of bony involvement may also ...