Histopathologic Features of Cutaneous Plexiform Schwannomas in Neurofibromatosis Type 2‐Related Schwannomatosis: Analysis of a Series of 19 Cases

IMPORTANCE: Neurofibromatosis type 2 (NF2)-related schwannomatosis is a genetic disease characterized by multiple tumors involving the nervous system. Some patients develop cutaneous schwannomas with characteristic histologic features that, if recognized, may have diagnostic and prognostic value. OBJECTIVE: To describe the clinical and histopathologic features of cutaneous schwannomas in a cohort of patients from a multidisciplinary NF2 clinic. DESIGN, SETTING, AND PARTICIPANTS: We have prospectively analyzed a series of 49 patients with NF2-related schwannomatosis and have selected the ones with superficial cutaneous schwannomas. We studied the histopathologic features of 19 cutaneous samples excised from 23 patients for diagnostic purposes or at patient's request from 2010 to 2023. RESULTS: Twenty-three patients out of 49 had superficial schwannomas. The mean number of superficial schwannomas per patient was 3.1, and they were all congenital or had appeared in childhood. Histologically, all superficial tumors studied corresponded to plexiform schwannomas with the particularity that in the adjacent dermis they showed hypertrophied nerves and also an infiltrating proliferation of Schwann cells with a tendency to surround cutaneous annexes and nerves. CONCLUSIONS AND RELEVANCE: Cutaneous plexiform schwannomas with hypertrophied nerves and an infiltrative Schwann cell proliferation may be a histologic clue to suggest a NF2-related schwannomatosis disorder.