Unilateral Sensorineural Hearing Loss Presenting With Bilateral Temporal Bone Lesions
Computed tomography (CT) of the temporal bones without contrast demonstrated expansion of the vestibular aqueduct without erosion on the right (Fig. 1A). On the left there was an 11 × 14 × 19 mm expansile lesion at the posterior petrous ridge with extension into the mastoid cavity and effacement of the mastoid segment of the facial nerve (Fig. 1B). T1-weighted magnetic resonance imaging (MRI) with gadolinium contrast showed patchy opacification of the left mastoid with a hyperintense lesion along the left posterior petrous ridge and a smaller hyperintense lesion along the right petrous ridge (Fig. 1C). Several punctate areas of enhancement in the cerebellum were also noted. T2-weighted MRI revealed the petrous ridge lesions to have heterogeneous hyperintense signals. Diffusion-weighted sequences showed no restriction. These radiographic findings suggested bilateral endolymphatic sac tumors (ELST) and cerebellar hemangiomas consistent with von-Hippel-Lindau (VHL) disease. Subsequent abdominal imaging was negative.
Endolymphatic sac tumors are low-grade, locally invasive tumors that arise from the epithelium of the endolymphatic duct and sac. They are commonly sporadic, although there is a well-established association with VHL disease (1). Sporadic ELST are often diagnosed in the fifth decade of life as compared with the third decade of life for tumors associated with VHL disease. Sporadic tumors have no sex predilection, while VHL-related tumors have a 2:1 female predominance. The most common VHL-related tumors are craniospinal hemangioblastomas occurring in 60 to 90% of patients with VHL disease. ELST on the other hand have a less predictable prevalence. The original incidence of ELST in VHL disease was reported at 16% (2). A recent population-based study through the International Endolymphatic Sac Tumor Registry identified only 93 ELST among 1,789 VHL patients, thus an incidence of 3.6% (3). Those with a VHL-related ELST have a 14 to 30% risk of developing a bilateral tumor (2,4).
The presence of any VHL-related tumor warrants careful evaluation for additional VHL-related tumors. In this case, close inspection of the asymptomatic contralateral side revealed a second ELST. Its early detection confirmed the VHL diagnosis and allowed a hearing preservation surgery. ELST identification is responsible for the VHL diagnosis in 32% of patients (3). Early diagnosis of VHL also facilitates monitoring of morbid conditions like renal cell carcinoma or other VHL-related tumors like pancreatic cysts and hemangioblastomas of the brain/cerbellum, spinal cord, and eye. There is no standard consensus for ELST monitoring in VHL. ELST screening should at least be performed at the time of VHL diagnosis and with any sudden hearing loss. Additional monitoring is at the discretion of the treatment team and based on an incidence rate of 3.6 to 16% (2,3).
Mukherji et al. (5) provide a comprehensive review of ELST radiologic characteristics. The rarity of ELST can make distinguishing them from paragangliomas, choroid plexus tumors, and metastases (renal and thyroid) challenging. On CT scan, ELST present as an enhancing soft tissue lesion with erosion of the posteromedial temporal bone. There will often be central spiculations and a posterior rim of calcification. Early lesions, like that shown in Figure 1A, may show dilation of the endolymphatic duct without erosion. Noncontrasted T1-weighted MRI may demonstrate hyperintense foci consistent with hemorrhage, while other portions of the lesion are isointense. T1-weighted postgadolinium and T2-weighted scans demonstrate heterogeneous signals that are hyperintense. Intralabyrinthine hemorrhage or inflammation can be observed on fluid-attenuated inversion recovery MRI and may accompany sudden hearing loss (5).