A female patient in her 70s was referred for image-guided biopsy of a perisplenic mass with malignant appearances. She had presented six years previously with persistent ulcerating skin lesions on her lower legs, and dermatological histologists gave a differential diagnosis of cutaneous T-cell lymphoma or lymphomatoid papulosis. Lymphoma staging CT revealed splenomegaly and a 6 × 4 cm, well circumscribed, heterogeneously enhancing perisplenic mass. However, bone marrow biopsy was unremarkable and, after discussion with the patient, haematologists elected to observe with serial CT imaging as they were unsure of the diagnosis. Over the next five years the patient remained well and on CT the mass was seen to be gradually enlarging, but with no invasion or infiltration of adjacent structures. However, six months prior to this referral, the patient developed a symptomatic pleural effusion, pulmonary hypertension on echocardiography, persistently elevated C-reactive protein, mild anaemia and considerable weight loss. Figure 1 shows the CT findings at this stage and Figure 2 is representative of the ultrasound images. Figure 1 (a, b) Contrast enhanced CT. An 11.4 × 8.2 cm heterogeneously enhancing mass is seen adjacent to the tip of the spleen. There are central areas of cystic degeneration/necrosis, ascites and splenomegaly, but no significant lymphadenopathy. Figure 2 Ultrasound examination with colour flow Doppler. The mass is hypoechoic, vascular and well defined. There is moderate ascites. What is the differential diagnosis, and how should we proceed? The differential diagnosis on the basis of clinical and radiological findings included lymphoma, hamartoma, gastrointestinal stromal tumour, vascular neoplasm, inflammatory pseudotumour and low-grade myofibroblastic sarcoma. Multidisciplinary team discussion agreed that a tissue diagnosis was required, but the patient was not keen for an open procedure, so percutaneous biopsy was performed under ultrasound guidance, without complication. Histology showed no evidence of malignancy. It comprised bland spindle cells, many vessels and small primary lymphoid follicles, representing myofibroblastic proliferation without normal splenic sinusoids. These findings are consistent with an inflammatory pseudotumour.