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Case Report
Intraorbital neuromuscular choristoma adjacent
to the optic nerve
Arie Perry M.D.
a,b,
⁎
, Jane W. Chan M.D.
c
,
Jennifer A. Cotter M.D.
a,b
, Adam Bracha M.D.
d
a
Department of Pathology, University of California San Francisco (UCSF) School of Medicine, San Francisco, CA, USA
b
Department of Neurological Surgery, University of California San Francisco (UCSF) School of Medicine, San Francisco, CA, USA
c
Department of Medicine, Division of Neurology, University of Nevada School of Medicine, Reno, NV, USA
d
Department of Radiology, VA Sierra Health Care System, Reno, NV, USA
Received 16 July 2015; revised 26 August 2015; accepted 2 September 2015
Abstract Neuromuscular choristoma is a rare tumor that incorporates mature skeletal muscle within
fascicles of peripheral nerve. The etiology is poorly understood, yet most present in large nerves of
children, with a tight link to post-operative fibromatosis recently appreciated. Herein, we report an
exceptional intra-orbital example in a 53-year-old man with optic nerve compression.
© 2015 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Neuromuscular choristoma (a.k.a. neuromuscular hamar-
toma, benign triton tumor, and nerve rhabdomyoma) is an
extremely rare peripheral nerve tumor with an admixture of
mature striated muscle and native neural elements [1].Upto
40–50 cases have been reported using looser definitions,
although some in optic or trigeminal nerves likely represent
other entities given the inclusion of smooth muscle and/or fat
[2]. Most involve larger nerves, such as brachial plexus or
sciatic nerve in children, although smaller nerve and
intracranial examples have also been reported. Intra-orbital
cases are exceptional, with only two other published cases to
our knowledge [3,4]. Herein, we report the third example.
2. Case report
A 53 year old man presented with one-year history of slowly
progressive left visual loss. He had intermittent sharp retro-orbital
pains and a gradually enlarging left central scotoma. On examination,
his best corrected visual acuity was 20/20 OD and 20/400 OS. He
had a left relative afferent pupillary defect. Extra-ocular motility was
normal. Dilated funduscopic examination revealed left optic atrophy.
MRI of the orbits with and without gadolinium disclosed an
enhancing 6 × 6 × 6.8 mm nodular lesion in the left orbital apex
abutting the inferior aspect of the optic nerve (Fig. 1AandB).He
underwent a subtotal resection of the tumor, which was lateral to
and separate from the medial rectus at the level of the orbital apex.
It grossly appeared as a soft, non-encapsulated, violaceous-brown
lesion, which was distinct from the intact left optic nerve.
Histopathology revealed fascicles containing both mature
striated muscle and peripheral nerve elements (Figs. 1 and 2).
No optic nerve or CNS parenchyma was seen. Histochemical
and immunohistochemical stains revealed S-100 (Fig. 2B)
and neurofilament (Fig. 2C) staining of Schwann cells and
⁎
Corresponding author.
E-mail address: arie.perry@ucsf.edu (A. Perry).
http://www.humanpathologycasereports.com
http://dx.doi.org/10.1016/j.ehpc.2015.09.001
2214-3300/© 2015 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
licenses/by-nc-nd/4.0/).
Human Pathology: Case Reports (2015) xx, xxx–xxx
axons respectively, with individual and grouped neural
elements surrounding skeletal muscle fibers. Strong desmin
expression was seen in the latter (Fig. 2A). An epithelial
membrane antigen stain highlighted perineurium surround-
ing each nerve fascicle. Perineurium was also seen focally
surrounding individual muscle fibers ( Fig. 2D). This
architectural pattern was consistent with the diagnosis of
neuromuscular choristoma.
3. Discussion
Neuromuscular choristoma is a poorly understood, but
benign intraneural tumor variably considered malformative
(choristoma or hamartoma, possibly due to muscle entrap-
ment during neural development or overgrowth of intra-
neural muscle spi ndles), metaplastic (transformation of
neuroectodermal elements into skeletal muscle), or neoplas-
tic (rhabdomyoma of nerve) in nature. They have been
variably reported to regress, remain stable, or recur following
surger y, with recent data suggesting that most of the
“recur rences” actually represent aggressive fibromatosis
(desmoid), detectable as low-density areas on MR imaging
[2]. Whereas most examples have involved large nerves in
children, cranial nerve examples have also been reported,
albeit more commonly in adults. To our knowledge, this is
only the third intra-orbital case and it likely arose from a
branch of the oculomotor nerve, with associated compression
and atrophy of adjacent optic nerve; nevertheless, the precise
origin was not obvious intraoperatively and the normal
ocular motility suggests that it did not involve cranial nerve
III proper. Prior intra-orbital examples have similarly
involved the apex, with reported origins either being unclear
or from the oculomotor nerve [3,4]. Familiarity with this rare
diagnostic entity can help avoid overly aggressive surgery.
References
[1] Perry A. Benign triton tumour. In: Fletcher CDM, Bridge JA,
Hogendoorn PCW, Mertens F, editors. WHO classification of tumours
of soft tissue and bone. Lyon, France: IARC; 2013. p. 185.
[2] Hebert-Blouin MN, Scheithauer BW, Amrami KK, Durham SR,
Spinner RJ. Fibromatosis: a potential sequela of neuromuscular
choristoma. J Neurosurg 2012;116:399-408.
[3] Bae DH, Kim CH, Cheong JH, Kim JM. Adulthood benign triton tumor
developed in the orbit. J Korean Neurosurg Soc 2014;56:146-8.
[4] Boyaci S, Moray M, Aksoy K, Sav A. Intraocular neuromuscular
choristoma: a case report and literature review. Neurosurgery 2011;68:
E551-5.
Fig. 1 Fat-saturated T1-weighted axial MRI of the brain without (A) and with (B) gadolinium demonstrates a rounded mass involving the
orbital apex adjacent to the left optic nerve. Intra-fascicular admixtures of mature nerve and skeletal muscle were evident on H&E (C; 200×)
and trichrome (D; 100 ×) stains, the latter highlighting muscular elements in red and collagen-rich neural elements in blue.
2 A. Perry et al.
Fig. 2 Immunohistochemistry revealed that the striated muscle fibers were desmin positive (A; 200×), whereas neural elements included
S100 positive Schwann cells (B; 200 ×), neurofilament positive axons (C; 400×), and epithelial membrane antigen positive perineurium
(D; 400×). Neural elements often surrounded individual immunonegative muscle fibers (arrows).
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