gms | German Medical Science

Objectives: Primary appendicular soft tissue lymphoma (ASTL) is rare.

Therefore, existing studies investigating ASTL characteristics are small scaled or consist of case reports [1]. Moreover, investigation criteria among existing studies are vastly heterogenous and differ in results. Consequently, ASTL are frequently not considered in the differential diagnosis of appendicular soft tissue masses, which may subsequently result in inadequate surgical or oncologic therapy.

Therefore, the purpose of this study was to identify specific and consistent clinical and MRI characteristics of ASTL.

Methods: We identified 23 Patients with histopathologically proven primary ASTL, who presented to our tumor surgery center between 2012 and 2021. Patient demographics, clinical and radiological presentation were evaluated. MRI scans were retrospectively assessed for characteristics such as: Encapsulation, multicompartmental involvement, infiltrative growth pattern, signal intensity (SI) compared to muscle, contrast-enhancement, growth along neurovascular bundles, presence of necrosis, subcutaneous stranding (SCS) and traversing vessels.

Results and conclusion: Patient age was 68 ± 14,8 years (range: 17-81) and 61% of patients were female. Pretherapeutic LDH levels were elevated in 60% of cases. Patients indicated pain in 45% and b-symptoms in 9% of cases. On MR imaging, soft tissue sarcoma (STS) was the most commonly suspected diagnosis (57%), while ASTL was suspected in 20% of cases.

T2W and PDW sequences showed hyperintense signal in all cases. T1W sequences showed isointense signal in 65% of cases and slightly hyperintense signal in 35% of cases. After application of contrast agent, T1W sequences demonstrated peripheral enhancement in 70% of cases, whereas 17% showed inhomogeneous and 13% showed homogenous enhancement. None of the ASTL in our study were encapsuled. 82% of ASTL showed an infiltrative growth pattern with 78% of ASTL not respecting compartmental boundaries. In 57% of cases, growth was orientated along neurovascular bundles. SCS was present in 66% and traversing vessels in 88% of cases. In 17% of cases necrosis was present.

Clinically, ASTL shows a heterogenous presentation and can be associated with pain, elevated LDH levels and lymphadenopathy.

The presence of hyperintensity in PDW and T2W MR sequences, peripheral contrast enhancement, subcutaneous stranding, traversing vessels, growth along neurovascular bundles, infiltrative growth pattern and multicompartmental involvement, paired with the absence of encapsulation should lead to the inclusion of ASTL in the differential diagnosis of soft tissue masses.

In contrast to current literature [2], the presence of necrosis does not rule out ASTL.

The most commonly suspected diagnosis in ASTL presentations is STS. However, STS rarely shows infiltrative growth pattern nor manifestation in subcutaneous tissue but rather respects compartmental borders, develops pseudo capsules and displaces neurovascular structures [3].