The Contradiction of a Benign Metastatic Meningioma: A Case Report.

Extracranial metastatic meningiomas are an extremely rare type of metastatic meningiomas. They are often asymptomatic and found incidentally on imaging. In this report, we discuss a young lady who presented with atypical chest pains, in whom initial work-up demonstrated a lesion in the left lung which was subsequently surgically resected. There was some confusion regarding whether the lesion was a primary pulmonary meningioma or a metastasising meningioma, both of which present similarly on histology with spindle or oval-shaped cells arranged in whorls. Further analysis revealed that this lesion belonged to a rare subgroup called 'benign metastasising meningioma', where the histology does not show the characteristic features of a metastatic lesion (such as high mitotic rate or evidence of necrosis). In fact, this lesion was found to have no necrosis, patternless growth, nuclear atypia or lymphovascular invasion and minimal mitoses occurring rarely despite metastasising from the meninges. This finding triggered further investigations in the form of brain imaging, which identified recurrence of a left central meningioma (a slow-growing tumour arising from the meninges on the left side of the brain), which was successfully treated 11 years previously. Neurosurgical intervention is currently being planned. Pulmonary meningiomas are extremely rare. In a patient with a history of a central nervous system meningioma, a pulmonary meningioma should be investigated further to assess whether the lesion is a primary or secondary metastasis.