Retroperitoneal synovial sarcoma

Case contributed by Hazem M Almasarei
Diagnosis certain


Presented to a general practitioner with an abdominal mass, who asked for an abdominal ultrasound that showed a well defined heterogeneous mass. Patient was then referred to the hospital.

Patient Data

Age: 15 years
Gender: Female

There is a relatively well-defined large heterogeneous enhancing soft tissue mass lesion in the left retroperitoneal region, with the following characteristics: it extends just below the inferior pole of the left kidney (but there is no communication with it), it reaches the left pelvis and splays the left psoas and iliacus muscles (there is an area that is inseparable from the mass which may suggest left psoas muscle invasion). It measures maximally 8 x 11 x 13 cm in three dimensions. It is surrounded by minimal stranding of fat planes. There is no vascular encasement. There is no associated lymph node enlargement. There is no bony involvement or extension of the spinal canal or exit foramina. The mass doesn't contain any fat elements. There is no ascites.

The rest of the abdominal visceral organs are unremarkable.



CLINICAL HISTORY: A case of retroperitoneal mass. 


  1. Retroperitoneal mass. 
  2. Peritumoral fat. 
  3. Psoas muscle. 


  1. The specimen is received in formalin, labeled with patient's name and "retroperitoneal tumor". It consists of a well-defined encapsulated round mass measuring 13x10x7cm. Sectioning shows homogenous white whorly cut surface. A piece of fatty tissue attached the tumor measures 8x4x3cm. Tissue submitted in 12 blocks. A: inferior margin. B: medial inferior margin. C: medial posterior margin. D: anterior lateral margin. E: medial superior margin. F: lateral margin. G-J: Tumor. K-L: peritumoral fat. 
  2. The specimen is received in formalin, labeled with patient's name and "Peritumor fat". It consists of one piece of fatty tissue measuring 8x4x1.5cm. Tissue submitted in 2 blocks. 
  3. The specimen is received in formalin, labeled with patient's name and "psoas muscle". It consists of one piece of muscular tissue measuring 2x1x0.7cm. All submitted in one block. 


  1. RETROPERITONEAL MASS; EXCISION: Spindle cell sarcoma consistent with monophasic synovial sarcoma,grade 2 (FNCLCC). See note. 
  2. PERITUMORAL FAT; EXCISION: Benign fatty tissue. 
  3. PSOAS MUSCLE; BIOPSY: Benign skeletal muscle fibers. 

NOTE: The tumor cells are positive for CD99 (weak to moderate), BCL2(focal) and EMA and focally positive for CK (AE1/AE3). They are negative for CD34, S100 protein, desmin, SMA, myogenin, and DOG-1. CK7 is positive in rare tumor cells. 

No necrosis seen. Mitotic activity is around 7/10 HPF. 

The nearest margin (anterolateral) is 0.8 mm away from tumor.  

Case Discussion

Synovial sarcomas are rare tumors that comprise only 1% of all malignancies. The retroperitoneum is an uncommon site of origin for them, accounting for 10% of all soft tissue sarcomas.

The other differential diagnoses are liposarcomas, leiomyosarcomas, malignant fibrous histiocytomas and malignant peripheral nerve sheath tumors. If there is associated lymph node enlargement, lymphoma should be considered.

Acknowledgments: Dr. Naim Qamhia, Pathologist, King Hussein Cancer Center, Amman, Jordan.

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