CASE 15191 Published on 23.11.2017

Extraskeletal osteosarcoma involving the mesentery and colon


Uroradiology & genital male imaging

Case Type

Clinical Cases


Ramon Martin F. Banez, MD; Johanna Patricia A. Canal, MD, MHA

University of the Philippines-Philippine General Hospital, Taft Avenue, Ermita, Manila

67 years, male

Area of Interest Abdomen, Bones ; Imaging Technique CT, Nuclear medicine conventional
Clinical History
A patient previously underwent left nephrectomy for angiomyolipoma.
Eight months post-nephrectomy, the patient noted a palpable mass in the left hemiabdomen.
Excision of the mass and segmental resection-anastomosis of the colon were performed.
Follow-up abdominal CT examination done five months post-operatively showed recurrence of the mass, for which chemoradiation and excision were done.
Imaging Findings
CT of the abdomen showed a 9.3 x 8.6 x 12.6-cm thick-walled heterogeneous mass with internal curvilinear calcifications in the left renal fossa.
Histological analysis of the excised mass showed a cellular intramural tumour involving the mesentery and colon. The tumour was composed of fascicles of spindle-shaped cells with extensive areas of osteoid formation, along with more focal chondroid formation (extraskeletal osteosarcoma).
Bone scintigraphy only showed degenerative changes in the shoulders, sacroiliac joints, knees, and feet. There was no suspicion of a primary bone tumour or bone metastases.
Follow up CT examination done five months post-operatively showed a 3.2 cm homogeneous, slightly enhancing mass adjacent to the left psoas muscle. Chemoradiation was performed; however, follow-up CT showed further increase of the volume of the mass. Surgery was performed with similar histological findings as in the previous operation.
Extraskeletal osteosarcoma (ESOS) accounts for 1% of all soft tissue sarcomas and 4% of all osteosarcomas [1, 2]. ESOS occurs predominantly in patients older than 40 years of age, in contrast to classic osteosarcoma, which shows a predilection in the first or second decade of life [3, 4]. The aetiology of ESOS is poorly understood. Some authors report occurrence in regions that were previously irradiated [5]. History of trauma as a possible cause has been hypothised as well [1].
The criteria for diagnosis of ESOS include 1) exclusion of a primary osseous origin; 2) the presence of a uniformly morphological pattern of sarcomatous tissue; and 3) the production of malignant osteoid or bone [3].
Common sites of involvement by ESOS are the lower extremity (47%), upper extremity (21%), and retroperitoneum (17%). Sites of metastases are the lung, regional lymph nodes, and bone [6].
CT usually shows a heterogeneous mass with varying amounts of internal mottled calcifications. A cystic component may also be seen, and the mass commonly exhibits areas of decreased attenuation, suggestive of necrosis [7].
MRI of ESOS may demonstrate a pseudocapsule. Areas of necrosis, chronic haemorrhage or secondary lacunae formation are seen as intermediate signal intensity on T1-weighted sequences and with very high signal intensity on T2-weighted images [8].
Radionuclide bone scintigraphy with Technetium-99m shows areas of avid tracer uptake. Pulmonary metastases, as well as non-calcified lesions in the brain and soft tissues, are also detectable on bone scans [9, 10].
Similarly, positron emission tomography (PET) with F-FDG shows focal accumulation of tracer in both primary tumour and metastatic sites. The intensity of tracer uptake is reported to correlate well with the aggressiveness of the tumour [11].
Radical resection of the tumour is the treatment of choice for primary ESOS. Favourable results have been reported with aggressive adjuvant multi-agent chemotherapy, similar to the treatment for conventional osteosarcoma [12]. Doxorubicin, cisplatinum, high-dose methotrexate and ifosfamide have been recommended for this purpose [13]. Radiotherapy may be indicated for temporary palliation [12].
Imaging has a major role in the diagnosis, treatment planning and follow-up of this tumour.
Differential Diagnosis List
Extraskeletal osteosarcoma involving the mesentery and colon
Metastatic osteosarcoma
Malignant fibrous histiocytoma
Liposarcoma (dedifferentiated)
Final Diagnosis
Extraskeletal osteosarcoma involving the mesentery and colon
Case information
DOI: 10.1594/EURORAD/CASE.15191
ISSN: 1563-4086