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.
Immunohistochemical analysis demonstrates diffuse and dark staining for S100 protein. This case was also positive for GFAP and dimly positive for actin (not shown).