Teaching Case

A 17-year-old female with complaints of vague abdominal pain and pyrexia of unknown origin was diagnosed to have a tubercular granulomatous abscess, in another institution. After showing no response to ATT for a few months, the patient was referred to our institute, for further management.

On admission, she denied any recent fever, cough, or loss of appetite. Physical examination revealed no pathological findings. Laboratory values upon admission showed raised ESR, and the rest of the values were unremarkable.

Ultrasonography (Figures 1a and 1b) revealed an ill-defined round heterogenous lesion with a central hyperechoic scar and internal vascularity. Fusion PET/ CT imaging with intravenous contrast (Figures 2a, 2b, 2c and 3) was further done to rule out malignancy, which showed bulky spleen with a well-defined round mass with lobulated margins showing heterogenous peripheral rim enhancement on arterial phase, heterogenous enhancement with slight hyper attenuation of radiating lines in venous phase and appearing isodense to splenic parenchyma in delayed phase. Low-dose FDG-PET revealed mild FDG uptake (SUV max 2.9) (due to low-dose PET, the typical radiating spoke wheel pattern could not be delineated), and the report suggested the possibility of abscess.

For definitive diagnosis, contrast-enhanced MRI (Figures 4a, 4b, 4c and 4d) was performed, which demonstrated a well-defined round lesion, iso to mildly hypointense on T1W sequence, mildly hyperintense to isointense with linear hypointense bands in a radiating pattern within the lesion in T2W sequence, mildly hyperintense signal on DWI with no evidence of low ADC values (Figure 5) and showing heterogenous contrast enhancement in peripheral and irregular septal components with progressive increase (Figure 6).

Based on imaging findings, a presumptive diagnosis of sclerosing angiomatoid nodular transformation (SANT) of the spleen was put forward; splenectomy was performed, and the diagnosis was confirmed by histopathological examination done on a post-operative specimen. On PET/CT (Figures 2a, 2b, 2c and 3), a focal hypodense lesion hyperenhancing on arterial phase with central non enhancing area and isoenhancing to liver in venous and delayed phases was noted in segment IV of liver, which on MRI (Figures 4a, 4b, 4c, 4d and 6) showed T1 hypointense and T2 hyperintense central scar, intense arterial phase enhancement with enhancing rim in hepatobiliary phase – concluded to be focal nodular hyperplasia.

SANT was first described as a distinct pathological entity by Martel et al. in 2004. According to the hypothesis for pathogenesis, an exaggerated proliferation of stroma causes an abnormal red pulp response because of smaller vascular outflow tract obstruction, which in turn causes vascular transformation of lymphatic sinuses [1,2]. In any patient presenting with a splenic lesion with an inflammatory or an angiomatoid component, the diagnosis of SANT should be considered [3].

Few of the patients present with abdominal pain, while others can present with splenomegaly, which has rarely been associated with leucocytosis, polyclonal gammopathy, and increased ESR [1].

The ultrasonography findings are usually inconclusive because SANT has variable appearance, variable echogenicity, sometimes internal septa, and usually internal vascularity [4].

In some literature, the appearance of SANT on CT is described as a solitary round, iso to hypodense mass lesion with lobulated margins with or without central calcifications, showing peripheral arterial phase enhancement with progressive centripetal filling in radiating pattern with central persistent hypodensity.

In MRI, it is known to show a “spoke-wheel pattern”, with the lesion being heterogenous, iso to hypointense on T1WI, and hyperintense on T2. On contrast administration, it shows peripheral and septal enhancing patterns persisting in venous and delayed phases with a hypointense central scar [5].

Based on the MRI appearance, it can be confused with angiosarcoma. Splenic hamartomas closely mimic the appearance of SANT and sometimes they also can present with a central scar. Heterogeneous appearance and FDG avid nature can raise suspicion of metastases.

There have been few reports of F-18 fluorodeoxyglucose (FDG) avid splenic lesions found to be SANT lesions mimicking metastases; however, other authors have reported SANT cases without PET activity [6].

It is agreed upon that differential diagnosis with only pre-operative imaging is difficult, because SANT is a rare entity. A definitive diagnosis may be masked by its close resemblance to other benign and malignant splenic lesions and there is scant literature available. Since percutaneous biopsy of the spleen is not a popular procedure in practice due to the underlying risk of bleeding and because of uncertain and overlapping imaging findings, definitive diagnosis is usually achieved by a histopathological and immunohistochemical workup of the lesion acquired after splenectomy.

Clinicians and radiologists should be cognizant of SANT of the spleen as a differential of splenic neoplasms, and knowledge of key imaging findings can help in arriving at the definitive diagnosis, followed by appropriate treatment and good prognosis.