Nerve sheath myxoma

Definition

This neoplasm is a type of nerve sheath tumour. It has been argued that this entity is distinct from neurothekeoma.

Epidemiology

These tumours occur over a wide age range, including children.

Clinical features

Tumours occur at a wide range of anatomical sites, with a predilection for the limbs, particularly for the fingers and around the knee. They are slow-growing.

Macroscopic appearances

Most tumours are not more than 2.5 cm in diameter at the time of resection.

Histopathology

The tumour occurs in the dermis and/or subcutis, rarely involving skeletal muscle. The tumour has a multinodular architecture surrounded by dense fibrous tissue. Cystic change may occur. The matrix consists of myxoid material with scanty collagen. Within the myxoid matrix, epithelioid Schwann cells form cords, nests or syncytial sheets. Some of these cells may have cytoplasmic invaginations giving a resemblance to adipocytes. Rarely, the nuclei show palisading. There may be a sparse lymphocytic infiltrate. The mitotic rate is low.

Immunohistochemistry

	S-100	40/401
	GFAP	19/191
	CD57	8/111
	NSE	4/51
	Cytokeratin cocktail (AE1/AE3 and LP 34)	6/18 showed positivity of infrequent cells1
	EMA	14/20 showed positivity of a few cells mainly at the periphery of tumour nodules1
	Muscle Specific Actin	2/8 showed positivity of a few cells1
	Neurofilament	2/10 showed positivity of rare cells1
	Factor XIIIa	0/81
	HMB45	0/81
	SMA	0/91
	Desmin	0/61
	CEA	0/41
	CD68	0/11
	CD31	0/11
	Synaptophysin	0/11
	Chromogranin	0/11

Differential diagnosis

Pre-operative clinical impressions may included epidermal inclusion cyst, ganglion cyst, bursa, tenosynovial giant cell tumor, traumatic neuroma, neurofibroma, Schwannoma, fatty tumor, fibrous histiocytoma, xanthoma, pyogenic granuloma and naevus.

neurothekeoma: occur predominantly in females in the first two decades, with a predilection for the face, shoulders and upper arm. They are less myxoid and show mitotic activity. Cords and nests of Schwann cells are lacking. There is negativity for S-100 and GFAP.
superficial angiomyxoma (cutaneous myxoma) also forms multinodular highly myxoid masses within the dermis and subcutis. Tumour cells are multinucleate and stellate. A peripheral fibrous margin is lacking. They are often positive for CD34 and are negative or weakly reactive for S-100. There is an association with Carney's complex.
peripheral nerve sheath tumors (including neurofibroma, plexiform neurofibroma, and Schwannoma)
chondroma of soft parts also occurs predominantly on the hands and feet. The myxochondromatous type have an abundant myxoid stroma. However, there are areas of cartilage; while the chondrocytes are positive for S-100, they are negative for GFAP.
superficial acral fibromyxoma focal mucinosis occurs on the fingers and toes where it is slow-growing. The amount of myxoid matrix is variable. Demarcation is less clear than in nerve sheath myxoma. They are positive for CD34, variably positive for EMA but usually negative for S-100.
digital mucous cyst
lipoma variants including liposarcoma
extraskeletal myxoid chondrosarcoma variant
myxo(fibro)sarcoma
mucinous carcinoma.

Management

Ideally, excision needs to be complete with a margin of normal tissue to reduce the likelihood of recurrence.

Prognosis

Local recurrences are common, particularly on the fingers.

References

1 Fetsch JF, Laskin WB,Miettinen M. Nerve sheath myxoma: a clinicopathologic and immunohistochemical analysis of 57 morphologically distinctive, S-100 protein- and GFAP-positive, myxoid peripheral nerve sheath tumors with a predilection for the extremities and a high local recurrence rate. Am J Surg Pathol 2005; 29:1615-24

This page last revised 29.7.2006.