Microcystic/reticular Schwannoma

Definition

A subtype of Schwannoma that shows a microcystic / reticular pattern and most often occurs in the gastrointestinal tract.

This tumour has been reported as occurring in the stomach, small and large intestine, bronchus, adrenal gland and subcutis. All patients have been asymptomatic or presented with a painless mass.

Histopathology

Gastrointestinal tumours are submucosal. The mass is unencapsulated and may be circumscribed or may infiltrate between smooth muscle fibres or into the mucosa entrapping epithelial crypts. The overlying epithelium may ulcerate.

The microcystic pattern comprised anastomosing strands of spindle cells with eosinophilic cytoplasm within a myxoid fibrillary or collagenised stroma. The microcysts contains myxoid material or fibrillary collagen. The nuclei are round, oval or elongated. Some cases include epithelioid foci, areas of classical Schwannoma, a prominent lymphocytic infiltrate or areas of foamy histiocytes.

Otherwise classical Schwannomas have been reported with a minor reticular component.

Immunohistochemistry

	S-100	10/101
	GFAP	10/101
	EMA	5/101
	SMA	0/51
	Desmin	0/51
	Neurofilament	0/61
	CD117	1/6(one case very focally positive)1
	MNF116	0/61
	AE1/AE3	0/61
	Cam5.2	0/61
	CD34	1/3(one case focally weakly positive)1
	Inhibin	0/21
	p63	0/21

Differential diagnosis

Within the gastrointestinal tract:

Classic Schwannoma of the gastrointestinal tract: also lack typical Antoni A and B areas: usually have a prominent lymphoplasmacytic cuff.
Mucinous adenocarcinoma: shows nuclear atypia: positive for cytokeratins.
Gastrointestinal stromal tumour : lack a microcystic appearance: positive for CD117:
Perineuroma: cells are elongated with bipolar processes: positive for EMA and 40% are positive for Claudin-1: S-100 and GFAP are negative.

Outwith the gastrointestinal tract:

Reticular perineuroma: usually occur on extremities: also shows a reticular pattern with myxoid stroma: cells are elongated with bipolar processes: positive for EMA: S-100 and GFAP are negative.
Myoepithelial tumour: nests and trabeculae of epithelioid and spindle cells in a chondromyxoid to hyalinised stroma: positive for MNF116, AE1/AE3, Cam5.2 and EMA.
Extraskeletal myxoid chondrosarcoma are multinodular tumours: may show a reticular pattern, only 20% stain for S-100, usually as scattered cells.

References