Trichilemmal cyst

A 75-year-old lady presented with transient loss of consciousness & altered sensorium one day ago.  At admission, she was conscious, oriented to place & person, obeying commands. There were no focal deficits.

Non-contrast computed tomography (NCCT) of brain was performed which showed no parenchymal pathology. Incidentally noted were multiple small iso to hyperdense lesions over her scalp in the right posterior temporal region, high parietal region, posterior midline in parietal region, & bilateral high frontal region. The largest one was 3 x 2.5 cm in size. Most of the lesions showed coarse calcification. There was no post-contrast enhancement. The underlying calvarium was intact (Fig 1-4). A diagnosis of trichilemmal cyst was made.

Trichilemmal cysts (TC) are keratin-filled cysts with a wall resembling the external root sheath of a hair follicle. They are encountered in 5-10% of population, more often in women & with average age of 65 years at presentation and may have autosomal-dominant inheritance [1,2].

They are usually soft in consistency measuring about 2-15 cm. Usually benign, TC arise in areas of dense hair follicle concentrations: about 90% of cases occur on the scalp while the residual 10% occur mainly on the back [1,3]. Occasionally the masses may become exophytic & may be associated with ulceration & may show malignant transformation [4].

On imaging, these lesions can be either a cystic or solid mass. Histopathologically, it is characterised by the absence of intercellular bridges between the epithelial cells lining the cyst wall. The peripheral layers demonstrate a palisading arrangement, whereas cells close to the cyst cavity are swollen and filled with pale cytoplasm. The cyst cavity contains amorphous eosinophilic keratin. Foci of calcifications within the keratin occur in approximately 25% of cases [5].