Leiomyoma of Deep Soft Tissue, Retroperitoneum, Mesentery and Omentum
Differential Diagnosis
- Leiomyosarcoma of soft tissue / smooth muscle tumor of uncertain malignant potential
- Gastrointestinal stromal tumor
- Parasitic leiomyoma
- Myofibroblastic and fibrohistiocytic tumors
In the deep soft tissue:
| Leiomyoma (requires all below) | Smooth Muscle Tumor of Uncertain Malignant Potential (used for any of below) | Leiomyosarcoma (requires any one of below) |
|---|---|---|
| Cytologically bland | Cytologic pleomorphism or atypia | |
| <1 mitotic figure / 50 HPF | Bland but 1-4 mitotic figures / 50 HPF | >4 mitotic figures / 50 HPF |
| No tumor cell necrosis | Multiple recurrences but lacking other atypical features | Coagulative tumor cell necrosis |
- Tumors arising in the muscularis propria of the GI tract and expressing CD117 should be designated GIST
Parasitic leiomyoma
- Parasitic leiomyoma must be clearly attached to the uterus or other organ
- In such cases, the criteria for smooth muscle tumors of that organ must be applied
- Elongate, eosinophilic cytoplasm
- Actin is not specific
- Desmin or caldesmon, if extensive, is more specific in this context
