This is a classic histologic example of a myxoid neurothekeoma, or nerve sheath myxoma. Clinically, they typically present on the head, neck, and upper extremities of middle age women, and therefore the location in this example is somewhat unusual. In difficult cases, the differential diagnosis may include cutaneous myxoma, mucus/myxoid cyst, myxoid neurofibroma, and mucinous adenocarcinoma. The lobular nature of this one is unmistakable. These lesions are usually S100 positive and GFAP positive, as in this case. They also stain with neuron specific enolase (NSE) and CD57. The cellular neurothekeomas are odd, expressing actin and only variably staining with neural markers.
Histologic sections of skin show a lobular spindle cell lesion within the dermis. The overlying epidermis shows mild acanthosis and papillomatosis. The spindle cells are in variably sized lobules with a mucinous/myxoid stroma and have thick fibrous septae. An inflammatory response is minimal.