MRI characteristics of appendicular soft tissue lymphoma: a retrospective analysis

Appendicular soft tissue lymphoma (ASTL) are rare and frequently misinterpreted as soft tissue sarcoma. This can put patients at risk. Existing studies evaluating MRI of ASTL are sparse, small scaled and report heterogenous results. The purpose of this study was therefore, to identify comprehensive MRI characteristics of ASTL.

We retrospectively analyzed demographic data, clinical presentation and MRI data of 26 patients presenting to our musculoskeletal tumor surgery center between 2011 and 2023 with histopathologically proven ASTL.

Identified MRI characteristics included a diameter larger than 5 cm (77%), hyperintense signal intensity in all T2-weighted, PD-weighted and short tau inversion recovery (STIR) sequences and iso- to slightly hyperintense signal intensity in T1-weighted sequences compared to skeletal muscle. Furthermore, irregular contrast enhancement of adjacent fasciae (60%) and predominant enhancement of peripheral tumor accompanied by slightly less intensive homogenous enhancement of the remaining tumor (55%) were observed. Additionally, regional lymphadenopathy (31%), subcutaneous stranding (58%), traversing vessels (88%) and the absence of encapsulation (100%) were discernable. Features seen in ASTL primarily involving muscle (n = 16), were involvement of multiple muscles (100%), tissue types (88%) and anatomical compartments (69%) as well as long segmental involvement (69%), growth along neurovascular bundles (56%) and partial or complete encasement of major vessels (81%). Intratumoral necrosis was identified in four cases (25%).

MRI provides the presented morphological indicators, that should raise suspicion of ASTL. Our findings suggest that necrosis may occasionally occur in pretreatment ASTL and its presence alone should not exclude lymphoma from the differential diagnosis.