![]() The surgical steps of ELS decompression comprise a wide canal wall-up mastoidectomy with decompression of the sigmoid sinus and the presigmoid dura, often referred to as the Trautman triangle. The estimated location of the ELS is just anterior and inferior to the junction of this line and the sigmoid sinus. This line is drawn along the long axis of the lateral semicircular canal (LSC) bisecting the PSC. 7 The Donaldson line is a useful surgical landmark to identify the ELS during ELS decompression. The location of the ELS is inferred at the terminal end of the endolymphatic duct at the dura of the posterior cranial fossa and just behind the posterior semicircular canal (PSC) ( Fig 1). On MR imaging, the endolymphatic duct that opens into the ELS at the operculum can be readily identified as a T2WI hyperintense structure. 5, 6 The ELS is not directly visualized on CT imaging one can, however, see the osseous margins of the vestibular aqueduct, which encase the membranous endolymphatic duct. 6ĮLS surgery, ie, either ELS decompression or ELS shunting, is a nonablative surgical option with moderate efficacy and little risk to hearing. Surgical treatment may be classified as “nonablative” (in which inner ear function is preserved), including endolymphatic sac decompression, or “ablative” (in which inner ear function is lost), including labryinthectomy and vestibular neurectomy. Treatment options for these patients with medically refractory symptoms include intratympanic corticosteroid injection, gentamicin injection, and surgery. 5 While many patients respond well to lifestyle changes such as low-salt diet and medical management with diuretics and betahistine, >20% of patients develop intractable Ménière disease. Although the physiology is debated, the endolymphatic sac (ELS) is thought to maintain hydrostatic pressure and endolymph homeostasis for the inner ear, and its dysfunction may contribute to the pathophysiology of this disease. 4 Endolymph is the fluid within the membranous labyrinth, including the vestibule, semicircular canals, and scala media of the cochlea. The pathophysiology is attributed to endolymphatic hydrops, a histologic finding in which the endolymphatic compartment including the scala media is dilated. Ménière disease is characterized by recurrent attacks of episodic vertigo, fluctuating low-frequency sensorineural hearing loss, tinnitus, and aural fullness. ![]() This review illustrates imaging findings after surgery for Ménière disease, superior semicircular canal dehiscence, temporal encephalocele repairs, internal auditory canal decompression, active middle ear implants, jugular bulb and sigmoid sinus dehiscence repair, and petrous apicectomy. The purpose of this image-rich review is to illustrate less common postoperative temporal bone CT findings that neuroradiologists may encounter and would ideally be able to recognize and to differentiate from disease mimics. Lack of familiarity with these surgical procedures and expected postoperative changes may render radiologic interpretation challenging. These postoperative temporal bone findings can have unique imaging features based on the type of surgical procedure and indication. Neuroradiologists may not be aware of these surgical procedures either due to the decreasing numbers of these surgeries performed today or some of the newer surgeries confined to specialized academic centers and thus less commonly encountered in routine practice. 1 ⇓- 3 Less common otologic procedures can present diagnostic dilemmas, particularly if access to prior operative reports is lacking. ![]() Many neuroradiologists may be familiar with the imaging appearance of the middle and inner ear, internal auditory canal, and lateral skull base after common surgical procedures such as ossiculoplasty, tympanomastoidectomy, cochlear implantation, and vestibular schwannoma resection. ABBREVIATIONS: AMEI active middle ear acoustic implants ELS endolymphatic sac LSC lateral semicircular canal MCF middle cranial fossa PSC posterior semicircular canal SSC superior semicircular canal SSCD superior semicircular canal dehiscence ![]()
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