Case studyIntranodal meningothelial proliferation in a patient with Cowden syndrome: a case report

•Extracranial meningothelial proliferations can occur in a multitude of anatomical locations.•Perineuriomas can histologically mimic extracranial meningothelial proliferations.•Extracranial meningothelial proliferation in a Cowden patient raises the possibility of a pathogenetic link.

SummaryEctopic meningothelial proliferations are rare and can occur in a multitude of extracranial/spinal anatomic locations. Perineurioma is another uncommon entity that shares similar histological characteristics to those found in meningothelial proliferations. These include bland spindle cells with thin, bipolar nuclei; eosinophilic cytoplasm; and indistinct cell borders, arranged in short fascicles with whorl formation. Given their uncommon occurrence and shared histological and immunohistochemical features, their distinction can present a diagnostic challenge. Immunohistochemical studies can provide guidance when attempting to distinguish between these 2 lesions. Here, we present an unusual case of a patient with Cowden syndrome who was discovered to have a meningothelial proliferation within an axillary lymph node. To the best of our knowledge, this is the first case in which a meningothelial proliferation has been identified in a lymph node. Furthermore, the occurrence in a patient with Cowden syndrome is intriguing and raises the possibility of a pathogenetic link.