Iliopsoas Neoplasm

R. Brooke Jeffrey, MD

Key Facts

Imaging

Best diagnostic clue
- Large retroperitoneal mass secondarily invading psoas
Location
- Psoas compartment
- Retroperitoneal spaces, including anterior and posterior pararenal spaces
Best imaging tool
- CECT, MR

Top Differential Diagnoses

Iliopsoas abscess
Iliopsoas hematoma

Pathology

Etiology
- Most often direct invasion by primary retroperitoneal or pelvic tumor
Associated abnormalities
- Primary pelvic or retroperitoneal tumor or nodes
- Bone destruction of spine

Clinical Issues

Most common signs/symptoms
- Back and leg pain
- “Psoas” sign with pain on lifting leg
- Palpable flank mass

Diagnostic Checklist

Consider well-differentiated liposarcoma if mostly mature fat in lesion
Image interpretation pearls
- Myxoid elements in liposarcoma appear cystic on MR

(Left) Axial CECT in a 71-year-old man with a 6 month history of an enlarging left flank mass reveals a large fat-attenuation mass occupying the entire left side of the abdomen and displacing the gastrointestinal tract to the right side of the abdomen. Note the direct infiltration of the left psoas muscle