Cutaneous heterotopic meningeal nodules.

The clinical, light microscopic and immunohistochemical features of six cutaneous heterotopic meningeal nodules (primary, or type I, cutaneous meningiomas) are described. These are rare lesions of the scalp and back which generally present at birth or in childhood. They appear as small subcutaneous fibrous nodules, with no specific clinical features although they can be associated with abnormalities of spinal closure. Microscopically, they show a variable architecture but have similar cytological features. Important diagnostic features include psammoma and small collagenous bodies. An intimate relationship to nerves is seen in some cases, and this may be of significance with regard to the development of these lesions. As with intracranial meningiomas, there is widespread vimentin expression, and most cases show epithelial membrane antigen expression.