White epidermoid at the foramen magnum

Raghvendra Ramdasi¹, Amit Mahore¹, Aadil Chagla¹, Juhi Kawale²,  
¹ Department of Neurosurgery, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Parel, Mumbai, Maharashtra, India
² Department of Medicine, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Parel, Mumbai, Maharashtra, India

Correspondence Address:
Raghvendra Ramdasi
Department of Neurosurgery, King Edward VII Memorial Hospital, Parel, Mumbai - 400 012
India

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A 20-year-old female presented with episodic occipital headaches and imbalance on walking of 2 years duration. Neurological examination showed hyper-reflexia of all four limbs. Computed tomographic (CT) brain scan showed a hyperdense lesion in premedullary cistern [Figure 1]a. Magnetic resonance imaging (MRI) of brain revealed a well-defined extra-axial lesion, 13 × 25 × 14 mm in dimensions with marked hyperintensity on T1-weighted images (T1WI) and hypointensity on T2-weighted image (T2WI). The lesion did not show any restriction of diffusion on diffusion-weighted imaging (DWI) and no enhancement on giving gadolinium [Figure 1]b-g. Gradient echo (GRE) sequence of MR imaging did not show any blooming [Figure 1]h. Based on the imaging features, a diagnosis of a high protein-containing cystic lesion was postulated. During surgery by suboccipital approach, a thin-walled extra axial cyst containing pearly and pultaceous material with viscous fluid was excised. There was no evidence of calcification. Patient was relieved of her symptoms after the surgery and was well at follow-up of 2 years. On histopathological examination, the cyst wall consisted of lamellated keratinizing squamous epithelium suggestive of epidermoid cyst [Figure 2]a and b.{Figure 1}{Figure 2}

Intracranial epidermoids are rare lesions accounting for 1% of all intracranial tumors. [1] Epidermoid tumors typically have long T1 and T2 relaxation times due to the presence of cholesterol in a solid crystalline state and keratin within the tumor. These are hypointense on T1-weighted, hyperintense on T2-weighted MR image and have no enhancement on post-contrast MR images. Epidermoid cysts are hypodense on CT scan. These typically restrict diffusion on DWI. In our case, the lesion was hyperdense on CT scan, hyperintense on T1-weighted image, hypointense on T2-weighted image, not enhancing by gadolinium and was not restricting diffusion on DWI.

Epidermoid tumors showing unusual signal intensity changes have been reported. These lesions are referred to as white epidermoid when these have short T1 values and fatty attenuation on CT as in our case. Their variable appearance can be linked to the biochemical nature and viscosity of the contents. It can show hyperintensity on T1- and T2-weighted MR images, caused by a semi-liquid cystic content with high protein concentration mixed with high triglycerides. It also can have high signal intensity on T1-weighted and low signal intensity on T2-weighted images, caused by even thicker toffee-like content with a combination of high protein content and high viscosity as in our case. An epidermoid tumor can show low signal intensity on both T1- and T2-weighted images, with a usual composition of epithelial debris, crystals of cholesterol and keratin. Variable signal on T1- and T2-weighted images may be because of recurrent intracystic hemorrhage and granulation tissue, often documented on histology. [2],[3] In our case histology did not reveal any hemosiderin-rich macrophages or granulation tissue. High protein content and high viscosity may be the reason of the unusual radiological picture.

The differential diagnosis of such radiological picture in the foramen magnum area can be neuroenteric cyst, post-hemorrhagic cystic mass as cystic meningioma and arachnoid cyst. [2]

Ectopic Rathke's cleft cyst constitute a rare possiblity. [4] Neuroenteric cysts are T2 hyperintense lesions, meningioma enhance on giving contrast and have dural attachments. The arachnoid cyst and Rathke's cleft cyst have smooth margins unlike epidermoids. [2],[4] After first reporting by Braun et al., in 1977, few cases of white epidermoid have been reported in the literature, most of which are in the cerebellopontine angle and few in the supratentorial region. [1],[2],[3] To the best of our knowledge, this is the first case of white epidermoid in the premedullary cistern near foramen magnum in the midline. The capsule of the epidermoid cyst often adheres to the surrounding structures. Accurate preoperative diagnosis can help prevent inadvertent damage to the surrounding vital structures as in our case and chemical meningitis due to spillage during surgery.

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