Unilateral Hearing Loss as the Sole Presentation of Extensive Intracranial Epidermoid Cyst: A Case Report

Abstract

Epidermoid cysts are rare congenital tumors of the central nervous system. These histologically benign, slow-growing lesions form when ectodermal cells become trapped during the closure of the neural tube. Histologically, they consist of a core composed of keratin, desquamated epithelial cells, and cholesterol, surrounded by a layer of stratified squamous epithelium. Clinical features depend on the lesion's location. In the cerebellopontine angle (CPA), they typically present with tinnitus, vertigo, hearing loss, and facial weakness, with or without cerebellar signs and symptoms. Unilateral hearing loss as the sole presenting symptom is uncommon in the setting of a large, extensive cyst and may delay diagnosis. A 35-year-old male presented with progressive left-sided hearing loss for one year, without vertigo, tinnitus, or other neurological symptoms. Audiological testing revealed severe-to-profound sensorineural hearing loss in the left ear. Temporal bone computed tomography and brain magnetic resonance imaging showed a large, extra-axial cystic lesion in the left CPA with characteristic diffusion-weighted imaging restriction, consistent with an epidermoid cyst. The lesion caused significant mass effect, including compression of the brainstem, cranial nerves, basilar artery, left vertebral artery, and left posterior cerebral artery. The patient underwent successful surgical excision via a retrosigmoid suboccipital craniotomy. Histopathological examination confirmed the diagnosis of an epidermoid cyst. This case report highlights an unusual presentation of an extensive epidermoid cyst in the left CPA that manifested solely as unilateral hearing loss, underscoring the diagnostic challenges posed by this rare lesion. The findings emphasize the importance of considering atypical presentations of intracranial tumors in the differential diagnosis of patients with unexplained hearing loss.

Keywords: cerebellopontine angle; cranial nerve compression; craniotomy; epidermoid cyst; hearing loss; inclusion cyst; intracranial tumor.

Figure 1. Preoperative MRI brain

A) T1-weighted imaging (T1WI) with contrast, coronal view; B) T1WI without contrast, sagittal view; C) T2-weighted imaging (T2WI) without contrast, coronal view; D) T2WI without contrast, sagittal view showing a large extra-axial lesion centered within the left cerebellopontine angle (CPA), extending inferiorly into the left cerebellar medullary cistern and superiorly into the left ambient cistern. It measures approximately 4.2 × 3.2 × 6.5 cm (anteroposterior × transverse × craniocaudal). The lesion indents multiple adjacent structures, including the medial aspect of the left thalamus, left suprasellar region, interpeduncular cistern, left mesial temporal lobe, optic chiasm, left optic nerve anteriorly, left cerebellar hemisphere, brainstem (midbrain and pons) with mild medullary mass effect, left cerebellar peduncle, and hypothalamus. The mass appears hyperintense on T2WI, hypointense on T1WI, and shows no contrast enhancement.

Figure 2. Preoperative MRI brain

A-B) Diffusion-weighted imaging (DWI), axial views: A) at the level of the cerebellopontine angle (CPA) and internal auditory canal; B) at the level of the midbrain and parahippocampal gyrus, both showing high signal intensity. C-D) Apparent diffusion coefficient (ADC), axial views: C) at the level of the CPA and internal auditory canal; D) at the level of the midbrain and parahippocampal gyrus, both showing signals similar to adjacent brain parenchyma with multifocal areas of restricted diffusion.

Figure 3. Preoperative MRI brain

Fast Imaging Employing Steady-state Acquisition (FIESTA) protocol, axial view at the level of the cerebellopontine angle (CPA) and internal auditory canal, showing a large extra-axial isointense lesion causing significant kinking and displacement of the left vestibulocochlear and facial nerves, along with compression and displacement of the pons.

Figure 4. Postoperative MRI of the brain

A-B) Axial views at the level of the midbrain: A) FIESTA protocol and B) T2WI without contrast, showing residual resected epidermoid cyst indenting the left occipital horn. C-D) Axial views at the level of the CPA and internal auditory canal: C) FIESTA protocol and D) T2WI without contrast, showing improvement in mass effect previously exerted by the epidermoid cyst, with resolution of the kinking and displacement of the left vestibulocochlear and facial nerves. FIESTA: Fast Imaging Employing Steady-state Acquisition: CPA: cerebellopontine angle; T2WI: T2-weighted imaging

Figure 5. Postoperative MRI of the brain

A) DWI axial view at the level of the midbrain, showing residual epidermoid evident by high signal intensity. B) ADC axial view at the same level, showing corresponding low signal intensity, confirming restricted diffusion. C) T1WI without contrast, sagittal view; D) T1WI without contrast, coronal view - both showing improvement in compression and displacement of the brainstem and left cerebellar hemisphere compared with preoperative images. DWI: diffusion-weighted imaging; ADC: apparent diffusion coefficient; T1W1: T1-weighted imaging