Challenges and pitfalls in diagnosis of Parosteal Osteosarcoma: A clinicopathologic study of 23 cases

Abstract

Objective: Parosteal Osteosarcoma (PO) is an uncommon variant of osteosarcoma. Diagnosing PO is important due to itsmalignant nature but the diversity of histologic features makes it challenging by adding a number of soft tissue, bony andcartilaginous lesions into the list of differential diagnosis. Our aim was to study the clinicopathologic and histological features ofPO with emphasis on features helpful in its discrimination from other mimicking lesions.

Methods: We reviewed 23 cases of PO diagnosed in our institution between January 2001 and August 2015.

Results: Femur was the most commonly involved bone (68.2%) along with other long bones and rib in a single case. Soft tissuecomponent was graded as Grade1 in 9(39%), Grade2 in 8(34.7%) and Grade3 in 4(17.3%) cases. Bony component was seeneither in combination of or exclusively as parallel streams and interconnected trabeculae (mosaic-pattern). Out of 9 cases withcartilage component, 3 showed a cartilage cap. 2(8.6%) cases showed dedifferentiation into osteosarcoma.

Conclusion: PO should always be considered in the differential diagnosis of every lesion arising from the bone surface.Knowledge of the variations in histologic features helps to reach the correct diagnosis which should never be made withoutradiological correlation.