Cerebral shading sign in a giant intraparenchymal white epidermoid

Anvita Puranik¹, Shilpa Sankhe¹, Naina Goel², Amit Mahore³,  
¹ Department of Neuroradiology, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Mumbai, India
² Department of Neuropathology, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Mumbai, India
³ Department of Neurosurgery, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Mumbai, India

Correspondence Address:
Amit Mahore
Department of Neurosurgery, King Edward Memorial Hospital, Parel, Mumbai - 400 012
India

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A 50-year-old female presented with bifrontal headache of two months' duration. Computed tomography (CT) of brain showed a well-defined hyperdense mass (7.3 × 6.2 × 5.6 cm) in the left basifrontal region with density ranging from 90-94 Hounsfield units [Figure 1]a. Magnetic resonance imaging (MRI) of brain revealed an intra-axial lesion with marked hypointensity on T2-weighted image (T2WI) and hyperintensity on T1-weighted images (T1WI) with minimal perifocal edema [Figure 1]b and c. A small solid component located antero-medially was hypointense on T2WI and isointense on T1WI with heterogeneous post-contrast enhancement. The lesion did not show any restriction of diffusion on diffusion-weighted imaging (DWI) [Figure 1]d. The cyst was non-enhancing [Figure 1]e and f. Based on these imaging features, a diagnosis of a high-protein-containing lesion like craniopharyngioma or neurenteric cyst was postulated. During surgery, a thin-walled intra-axial cyst containing xanthochromic pultaceous material and viscous fluid along with a solid nodule in the antero-medial location were excised. There was no evidence of calcification during surgery. Patient was relieved of her symptoms after the surgery. She has no neurological deficit at 14-month follow-up. On histopathology, the cyst wall consisted of lamellated keratinizing squamous epithelium [Figure 2]a. Foamy histiocytes, foreign-body giant-cells and cholesterol clefts were also seen, suggestive of an epidermoid cyst with focal granulomatous inflammation [Figure 2]b. There was no calcification.{Figure 1}{Figure 2}

Intracranial epidermoids are developmental lesions accounting for 1% of all intracranial tumors. [1] These commonly occur in cerebellopontine angle and rarely present as supratentorial, intraparenchymal masses. On CT and MRI, epidermoids are of cerebrospinal fluid (CSF) density and are non-enhancing. [2] "White epidermoids" appear hyperattenuated on CT, and can show reversed signal intensity on MRI, with high signal intensity on T1WI and low signal intensity on T2WI. [1],[3] This loss of signal on T2WI due to highly viscous proteinaceous debris is termed as the "Shading Sign". [4] This sign has been previously described in endometriotic cysts having high viscosity due to concentration of protein and iron from recurrent hemorrhage. [4] High protein content alone cannot lead to this appearance as exemplified by simple hemorrhagic cysts which are bright on T1WI but do not show "Shading Sign" as their viscosity is low. [4] The term "Intracerebral Shading Sign" has been described in hemorrhagic metastases of squamous cell carcinoma having high viscosity and proteinaceous ferrous contents, but not with epidermoid cysts. [4],[5] During surgery, we did not find any acute hemorrhage inside the cyst, but we found xanthochromia of contents, which is a hallmark of chronic recurrent hemorrhage. The differential diagnosis for this lesion would include hemispheric craniopharyngiomas and neurenteric cysts. Craniopharyngiomas commonly contain calcifications. Neurenteric cysts with high protein content can be differentiated easily during surgery, as these do not contain pasty material like epidermoid, instead these contain only viscous fluid.Their common location is usually in the midline in front of the brainstem. [6] Restriction on DWI is seen in classic extra-axial epidermoids. It may not be very useful in characterization of intraparenchymal epidermoids which have variations in MR signal intensity due to the different chemical components and physical states of the lesion contents. [7] In our patient, the lesion did not show restriction of diffusion. We also believe that MR spectroscopy may not help in the differential diagnosis of these lesions. Intraparenchymal white epidermoids with the classic "Shading Sign" is an extremely rare presentation. To the best of our knowledge, only two cases of supratentorial intra-axial white epidermoids have been reported. Accurate preoperative diagnosis can help prevent possible chemical meningitis during surgery.

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