Meningothelial Hamartoma of the Scalp: Clinicopathologic Review of an Unusual Tumor Mimicking a Vascular Neoplasm with Review of Literature

Introduction/Objective Benign meningothelial hamartoma of the scalp is a rare entity with only scattered case reports existing in the literature. The hamartomatous process is believed to occur secondary to ectopic displacement during embryogenesis with the migration of meningothelial cell precursors to the incorrect location or secondary to an obliterated meningocele. This tumor may be easily missed and may be misdiagnosed as lipoma or sometimes as cutaneous angiosarcoma due to the several histologic features that mimic the histology of a vascular neoplasm. Methods/Case Report We report an unusual benign skin lesion occurring in a 19-year-old man with no significant past medical history. The lesion had been present since he was an infant and had been slowly enlarging over the past 15 years. The lesion caused pain and discomfort and the patient underwent an excisional biopsy of the lesion. Histologic examination showed a subcutaneous lesion with ill-defined borders and peripheral areas of infiltration between adnexal structures. Immunohistochemistry performed on the tumor cells showed that they were positive for EMA, progesterone receptor, D2-40, and vimentin. A next-generation sequencing study using a hybrid capture-based panel examining 50 commonly mutated genes in human neoplasia was performed and showed no molecular alterations supporting the benign or non-neoplastic nature of the lesion. Along with this case, we review 20 cases of meningothelial hamartomas from 13 papers and summarize them in the table. Results (if a Case Study enter NA) N/A Conclusion To our knowledge, this is the first reported case of one of these lesions with associated molecular genetic testing. The molecular study carried out, in this case, did not disclose any genetic variants commonly associated with human neoplasia supporting the notion that this lesion does not represent the neoplastic process but rather a hamartomatous process. Meningothelial hamartoma is an exceedingly rare, benign lesion that may be confused with a low-grade vascular neoplasm due to its rare nature and unusual histologic features.