Epidermoid of skull vault
Presentation:
Enlarging lump above right orbit.
Patient Data:
MRI demonstrates an expansile lesion centred in the right frontal bone adjacent to the right frontal sinus measuring 4.4cm * 1.9cm). It is well-defined. There is some extra-osseous extension into the subcutaneous tissue (best seen on the T2 GRE images). It is hyperintense on T2 weighted imaging, iso-intense on T1 weighted imaging. It is of intermediate signal on DWI without associated decreased in ADC values.
Within it there is dependant / posterior debris seen within it which is hyperintense on T1 imaging. The periphery of this lesion enhances. There dura / periosteum seen adjacent to this lesion (intracranial and intra-orbital) demonstrates enhancement. No flow voids seen within this lesion. The pituitary stalk is normal. No other lytic lesions seen within the visualised skull.
The visualised brain has normal appearances.
The patient went on to have resection and cranioplasty.
Histology
MICROSCOPIC DESCRIPTION: Paraffin sections show a cyst lined by a thin layer of squamous epithelium. A small amount of keratin is noted within the cyst lumen. No appendageal structures are identified and there are no mesenchymal elements. The cyst wall is composed of vascular granulation tissue containing patchy infiltrates of plasma cells, lymphocytes and and CD68+ histiocytes. Small trabeculae of viable bone are present within this tissue. The features are of an epidermal cyst. No evidence of tumour is seen.
DIAGNOSIS: Epidermal cyst.
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