Dilation of the Subarachnoid Spaces Surrounding the Cranial Nerves with Petrous Apex Cephaloceles in Usher Syndrome

Abstract

SUMMARY:Limited studies of brain MR imaging findings in Usher syndrome have reported atrophy with enlarged subarachnoid spaces. However, the specific appearance of the subarachnoid spaces surrounding the cranial nerves has not yet been described. Herein we describe the skull base MR imaging findings in an adult with Usher syndrome. Multiple cranial nerve exits were enlarged to the point of causing cephaloceles with bony remodeling. A combination of uncommon findings in this rare disorder raises the question of an etiologic association. Usher syndrome, also called Graefe-Usher syndrome, is a rare, congenital, autosomal recessive disorder characterized by retinitis pigmentosa and sensorineural hearing loss, as first described by Von Graefe in 1858.1,2 In the United States, the prevalence is estimated at 4.4 per 100,000.1 Usher syndrome stems from a variety of genetic mutations for which a common mechanism is not well understood.3 This syndrome is divided into 3 clinical subtypes on the basis of the temporal course and the extent of deafness: type I patients exhibit profound hearing loss and lack of vestibular function; type II patients have moderate to severe hearing loss with preserved vestibular function; and type III patients have milder progressive hearing loss, with approximately half having vestibular deterioration.3 The CT and MR imaging literature describing Usher syndrome is sparse but describes diffuse brain atrophy and enlargement of the subarachnoid spaces with diminished cerebral and posterior fossa tissue volumes.4-6 There has not yet been a description of whether the subarachnoid space enlargement involves the transit points of the cranial nerves along the skull base.A petrous apex cephalocele (PAC) is an uncommon lesion consisting of congenital or acquired herniation of the contents from the Meckel cave, which may cause remodeling of the adjacent petrous temporal bone.7 On pathologic examination, these have been defined as either meningoceles or arachnoid cysts.7 These lesions are usually incidental and unilateral but rarely may be symptomatic.Here we report the case of an adult with type I Usher syndrome, in whom MR imaging demonstrated diffuse dilation of the subarachnoid spaces extending along the cranial nerves to the point of causing bony remodeling from PACs. The presence of these uncommon findings in a patient with this rare disorder raises the question of an etiologic association. Case ReportA 58-year-old man with type I Usher syndrome (per ophthalmologic diagnosis) and baseline ocular blindness and sensorineural hearing loss presented initially with temporal pain underlying the right temporomandibular joint. An MR imaging examination was performed on a 3T scanner to exclude an intracranial cause, consisting of axial fast spin-echo (FSE) T2-weighted images (T2WI), diffusion, and fluid-attenuated inversion recovery images through the whole brain (5-mm thickness), with thinner 3D FSE T2WI images through the skull base (0.6 mm), as well as precontrast and postcontrast axial and coronal T1-weig...

Lesions of the Petrous Apex: Classification and Findings at CT and MR Imaging

“…They are thought to be caused by chronically increased intracranial pressure that is transmitted into the Meckel cave through a patent porus trigeminus. Petrous apex cephaloceles are associated with empty sella and Usher syndrome, are usually bilateral, and occur more often in women than in men (19,20). The lesions may be incidental findings but occasionally may erode into the otic capsule or pneumatized petrous apex cells, resulting in headaches, hearing loss, or CSF otorrhea (21).…”

Recurrent meningitis in a child with bilateral cochlear implantation associated with a petrous apex encephalocele: a case report and literature review

“…The majority of cases (72%) have been reported in adults with a minority (28%) reported in children. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] 70% of the reported cases of pediatric PACs (including this report) were associated with infectious complications such as meningitis [17][18][19]30] compared to only 12% of adult cases. [14,15,26] This may reflect an increase risk of meningitis in children or possibly difficulty of children to report other symptoms that could present before infectious complications.…”

Cerebrospinal fluid leak with recurrent meningitis following tonsillectomy

“…14 Twentyfive PACs have been reported in the literature, with only 3 patients demonstrating bilateral lesions. 18 Because they are usually asymptomatic, the incidence of PACs is not well established, but has been estimated to be between 1/10,000 and 1/100,000. 9,11,13 A PAC may be either congenital or acquired.…”