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Cranial Fasciitis

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Microscopically, cranial fasciitis resembles nodular fasciitis and is composed of fibroblasts and myofibroblasts in myxoid or hyalinized matrix. Osseous metaplasia may be present. In this image, the spindle cells lack cytologic atypia. They are separated by keloid-type collagen. Delicate capillary-caliber vascular channels and a few extravasated red blood cells are additional findings seen here.

Cranial fasciitis is a benign reactive process arising from galea aponeurotica (epicranial aponeurosis). The etiology is related to trauma such as that caused by forceps delivery or prior craniotomy. Rare cases have been reported in patients with familial adenomatous polyposis. The strong nuclear immunoreactivity for beta-catenin in these cases suggests a role for dysregulated Wnt/beta-catenin pathway.

Like nodular fasciitis, rearrangements of ubiquitin-specific protease 6 gene (USP6) on chromosome 17p13 have also been reported in cranial fasciitis. This gene codes for a de-ubiquitinizing enzyme that is involved in many vital cellular processes, including intracellular trafficking, inflammatory signal response, and protein metabolism. The usual fusion partner of USP6 is MYH9 on chromosome 22q13.1.

Identification of t(17;22)(p13;q13) by traditional cytogenetics is quite challenging as the chromosomal breakpoints are located at the ends of the involved chromosomes. However, RT-PCR and FISH are highly specific and sensitive in detecting MYH9-USP6 fusion.

Reference: Salib, C et al. USP6 Gene Rearrangements by FISH Analysis in Cranial Fasciitis: A Report of Three Cases. Head Neck Pathol 2019 Feb 13.

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