Smooth muscle tumours of the small intestine

True smooth muscle tumours of the small intestine

Definition

Most mesenchymal tumours of the small intestines are gastrointestinal stromal tumours. A minority (~3%) are true smooth muscle tumours.

Clinical features

Presentation may be with gastrointestinal haemorrhage or obstruction due to intussusception, less often with perforation.

Histopathology

Leiomyomas are composed of fascicles of uniform spindle cells with eosinophilic cytoplasm and lacking nuclear atypia. There may be cytoplasmic eosinophilic globules. The mitotic rate is low (up to 3 per 50 HPF). Nuclear palisading, perinuclear vacuolation and skeinoid fibres are not see.

Leiomyosarcomas show a significant mitotic rate (more than 35 per 50 HPF) and/or necrosis. There is nuclear atypia of variable severity.

Immunohistochemistry

	Leiomyoma	Leiomyosarcoma
SMA	6/61	11/111
Desmin	6/61	6/81
CD117	0/61	0/111
oestrogen receptors	0/3(tumours in women)1
CD34		0/81
S100		0/71

Molecular findings

These tumours retain wild-type KIT and PDGFRA sequences.

Differential diagnosis

Uterine smooth muscle tumours that become externally attached to the intestines: they are positive for oestrogen receptors and progesterone receptors. Uterine leiomyosarcomas are less often positive for oestrogen receptors.
Dedifferentiated liposarcoma with smooth muscle differentiation.
gastrointestinal stromal tumour: cytoplasm is less eosinophilic, positive for CD34 and CD117.

References

1 Miettinen M, Sobin LH, Lasota J. True smooth muscle tumors of the small intestine: a clinicopathologic, immunhistochemical, and molecular genetic study of 25 cases. Am J Surg Pathol. 2009 Mar;33(3):430-6.