White epidermoid masquerading as meningioma on CT

A 62-year-old male presented with a history of a headache on and off for one year and weakness in the right upper and lower limbs for one year. He had no other complaints. On examination, power was 4 out of 5 in the upper and lower limbs. All laboratory investigations done were within the expected range.

A non-contrast CT (NCCT) scan shows a well-defined lobulated hyperattenuating lesion with a smooth margin in the subfalcine region of the anterior cranial fossa. The lesion has no internal calcification/surrounding oedema; however, there is a mass effect on bilateral lateral ventricles.

Magnetic resonance imaging (MRI) shows the lesion to be well-circumscribed and in an extra-axial location. The lesion appears bright on T1W images and predominantly hypointense on T2W images. Signal intensity on fluid-attenuated inversion recovery (FLAIR) images is similar to T2W images. The lesion shows no significant diffusion restriction/ post-contrast enhancement.

Epidermoid cysts are benign tumours formed from retained ectodermal elements. These tumours account for < 1% of intracranial tumours [1]. They are extra-axial tumours, with common locations being cerebellopontine angle cistern, prepontine, suprasellar, and para-sellar region [2].

Typically, epidermoid cysts are hypodense or isodense to CSF on NCCT. Rarely, they may appear hyperdense due to high protein content or mixed triglycerides, called white epidermoids. 1977 Braun et al. described the intracranial lesion as a “dense epidermoid cyst” due to its hyperattenuating imaging on NCCT [3]. Internal calcifications are not reported in such lesions.

Epidermoids are hypointense on T1W and hyperintense on T2W images with significant diffusion restriction.

Unlike epidermoids, white epidermoids appear bright on T1W images due to high protein or lipid content and do not show diffusion restriction because of variable internal content [4,5]. According to Bohara et al., the hypointense signal on DWI is caused by the xanthochromic fluid content, which results from microbleeds [6]. Hypointensity on T2W images is attributed to the high viscosity due to proteinaceous contents [1].

Post-contrast imaging appearance of white epidermoids is similar to typical epidermoids and shows no enhancement/mild peripheral enhancement.

A complete surgical excision was done in our case. A creamish-yellow soft, non-vascular, partly suckable tumour was excised. Histopathology of the lesion removed was suggestive of an epidermoid cyst.