White epidermoid at the foramen magnum

Abstract

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 1a]. 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 1b-g]. Gradient echo (GRE) sequence of MR imaging did not show any blooming [ Figure 1h]. 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 2a and b].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.

Evolution of epidermoid cyst into dermoid cyst: Embryological explanation and radiological-pathological correlation

“…Most of the white epidermoid cysts reported in the literature belong to this category. 15,16 Out of the 15 cases of hyperdense epidermoids reported by Li et al, 17 six patients had MRI. All of them showed a hypointense signal on T2WI and five of them showed an iso to hyperintense signal on T1WI.…”

White epidermoid of the sylvian fissure masquerading as a dermoid cyst: An extremely rare occurrence

“…So epidermoids which are white or hyperintense on T1 are labeled as white epidermoids and are usually hypointense on T2 and show no diffusion restriction. [1689] The loss of the signal intensity on T2WI sequence of MRI due to highly viscous and proteinaceous contents of the white epidermoid cyst has also been termed as the “Shading Sign.”[8] This is not to be confused with the term “Intracerebral Shading Sign” which is used specifically for the hemorrhagic metastases of squamous cell carcinoma. [10]…”

White Epidermoid with the “Cerebral Shading Sign”

“…Classically, epidermoid tumors are hypodense on CT scans and hypointense on T1-weighted and hyperintense on T2-weighted MR images with restricted diffusion on diffusion-weighted images. Such appearance is due to the long T1 and T2 relaxation times of cholesterol in solid crystalline state and keratin within the cystic lesion (1).…”

“…Compared with classic epidermoid cysts, the white epidermoids show reversed signal intensity on MR images, with high signal intensity on T1-and low signal intensity on T2-weighted images. High protein density, high viscosity, granulation tissue, and hemorrhage are the reasons for reversal of the usual hypodense appearance of epidermoid (1,2). The differential diagnosis for white epidermoids includes craniopharyngiomas and neurenteric cysts.…”