Splenic inflammatory (myofibroblastic) tumour: CT and MRI findings

Clinical History

Asymptomatic elderly woman with unremarkable medical history including chronic autoimmune thyroiditis. Recent incidental finding of a sizeable, mixed hypoechoic splenic lesion at routine abdominal ultrasound, not reported in previous ultrasound studies performed years earlier. Normal findings at physical examination. No significant laboratory abnormalities (haemoglobin 12.8 g/dL; 210.000 platelets/mmc; normal coagulation).

Imaging Findings

CT (Fig. 1) confirmed well-demarcated 6x4.5 cm ovoid mass at the upper splenic pole, mildly hypoattenuating compared to the splenic parenchyma, with inhomogeneous peripheral enhancement which progressed from the arterial over the portal venous and equilibrium phases. No other abormal findings were present in the thorax, abdomen and pelvis.
Since malignancy could not be excluded, further investigation was requested. Six weeks later, MRI (Figs. 2, 3) confirmed solid splenic lesion with unchanged size, low peripheral T2-signal intensity, unrestricted diffusion with indeterminate apparent diffusion coefficient (ADC) value (0.9) and lesion-to-spleen ADC ratio (0.85). The dynamic post-gadolinium study confirmed inhomogeneous arterial hypervascularisation with progressive enhancement during the portal and venous phases, and central hyperenhancement in the equilibrium phase suggesting desmoplastic / fibrotic component.
Laparoscopic splenectomy was performed. The brownish-grey mass at cut section showed histopathology findings including myofibroblasts and associated heterogeneous inflammatory infilatrate with lymphocytes and plasma cells, consistent with inflammatory pseudotumour.

Discussion

Inflammatory pseudotumours (IPTs) are uncommon benign tumour-like lesions which affect the orbit, lungs, and occasionally a variety of other organs including the gastrointestinal tract, liver, heart, bladder and thyroid. Splenic IPTs are exceedingly rare, with approximately 115 cases reported in recent literature review. The pathogenesis is debated, and possible aetiologies including immunological derangement, viral infections and parenchymal infarction have been speculated. Causative microorganisms have never been detected, albeit approximately 41% of cases tested positive for Epstein-Barr virus RNA [1-7].
Histologically, splenic IPTs are well-circumscribed solitary masses composed of myofibroblastic spindle cells, intermixed with heterogeneous cellular infiltrate predominantly composed of plasma cells and lymphocytes. The key differential diagnosis is the exceptional follicular dendritic cell sarcoma, which is closely similar at imaging but shows atypical myofibroblasts and behaves more aggressively [1, 2, 6-8].
Splenic IPTs occur from 20 to 80 years of age in both sexes, is commonly asymptomatic and incidentally detected in two-thirds of cases because of increased use of imaging. Manifestations include nonspecific upper abdominal discomfort or pain, weight loss, sometimes fever and splenomegaly. Laboratory studies are normal or may indicate chronic inflammatory response with anaemia, thrombocytosis, polyclonal hypergammaglobulinaemia [1-7].
Splenic tumours are often challenging for the radiologist, and imaging does not allow confident differentiation of IPT from other lesions, particularly lymphoma and metastases. IPTs range from 3 to 22 cm, and commonly measure over 10 cm. Sonographically, IPTS appear as demarcated hypoechoic or partially calcified echogenic masses, hypovascular on colour-flow Doppler ultrasound. The CT appearance includes low- or isoattenuating lesions with variable, mild or heterogeneous early enhancement, gradual filling during the venous and delayed phases. The same pattern is demonstrated at dynamic contrast-enhanced MRI. IPTs have isointense T1- and either increased or decreased T2-weighted signal: as in this case, MRI may allow differentiation from strongly T2-hyperintense splenic masses such as haemangioma, lymphangioma, abscesses and necrotic tumours [3, 9]. On positron-emission tomography (PET)-CT these lesions show variable, often intense uptake [2].
Unfortunately IPTS generally masquerades as a splenic malignancy. Fine-needle and core biopsies are not recommended due to poor diagnostic yield, potential bleeding and fear of neoplastic dissemination. Although surgeons may be reluctant to remove asymptomatic masses, surgery is indicated even if IPT is suspected, since only histopathology establishes the diagnosis. Splenectomy is the mainstay treatment and increasingly performed laparoscopically. After splenectomy, the prognosis is favourable: metastases, local invasion or recurrence have been never reported [1, 3, 10-12].

Differential Diagnosis List

Final Diagnosis

Inflammatory (myofibroblastic) pseudotumour of the spleen

URL:	https://eurorad.org/case/13713
DOI:	10.1594/EURORAD/CASE.13713
ISSN:	1563-4086