Sclerosing angiomatoid nodular transformation of the spleen

An asymptomatic 33-year-old woman was referred to our oncologic hospital due to an unusual splenic lesion found during an abdominal ultrasound. No relevant previous medical history.

CT was the first imaging modality performed for better characterization. At axial (fig.1) contrast-enhanced CT, we can appreciate a large, solitary, well-circumscribed splenic mass with smooth borders on the anterior pole of the spleen, heterogeneously enhancing in the portal phase.

Axial T1-weighted (fig.2) image of the abdomen demonstrated a large mass with heterogeneous iso to hypointense signal intensity. Axial (fig.3) and coronal (fig.4) T2-weighted MR depict a predominantly low signal mass with a centrally scattered high signal intensity.

In the arterial phase (fig. 5) we see heterogeneously hypoenhancing lesion with progressive enhancement on the late phase images from the periphery toward the centre of the lesion (fig. 6) in a "spoke-and-wheel" pattern. On delayed phase images (fig.7), the lesion is near isointense relative to the spleen.

Sclerosing angiomatoid nodular transformation (SANT) is a rare non-neoplastic benign vascular lesion of the spleen of unknown etiopathogenesis with a female predominance. The majority of the patients are asymptomatic at presentation and SANT is identified incidentally on imaging. Some patients may present with abdominal discomfort or pain. [1] SANT show characteristic CT and MRI findings that reflect the underlying pathology. On histopathology, there are dense areas of fibrosis and angiomatoid nodules. [1,2]

SANT is usually a well-circumscribed solitary splenic mass with smooth or lobular contours.

At ultrasound SANT usually presents as a heterogeneously hypoechoic mass.

At computerized tomography (CT), SANT presents as a well-circumscribed solitary mass that is homogeneous and predominantly isodense compared to surrounding spleen at unenhanced images. After contrast administration, this lesion has lower attenuation relative to background spleen with peripheral enhancing radiating lines on early phase and progressive heterogeneous in “spoke-and-wheel” pattern enhancement on portal venous phases. On delayed phase contrast-enhanced images the lesion becomes near isointense compared with the spleen except for the hypovascular central scar [3, 4,5].

On T1-weighted images, most of these lesions have a heterogeneous low to intermediate signal intensity.  On T2-weighted images, most of these lesions are typically heterogeneous hypointense mass relative to the signal intensity of background spleen with hyperintense central scar. After gadolinium administration, SANT has a peripheral and septal radiating enhancement in a “spoke-and-wheel” pattern with a central hypoenhancing stellate scar on delayed phase, as above described. [4,5,6,7]

SANT shows s hypermetabolic activity with a slightly increased accumulation on F-18 -fluorodeoxyglucose - positron emission tomography [3,5]

SANT is a benign lesion that has no risk of malignant transformation. Splenectomy is often performed to confirm the diagnosis since it allows a definitive histopathological and immunohistochemical characterization, allowing differential diagnosis with malignant lesions of the spleen. [4,8] Since our patient refused surgery, imaging follow-up was performed during a period of 5 years, revealing lesion stability over this period of time. The imaging features and lesion stability allowed us to be confident in this diagnosis.

Radiologist should be aware about SANT and it should be considered in the differential diagnosis of the evaluation of splenic nodules. The presence of a “spoke-and-wheel” pattern on the dynamic MR studies suggest the diagnosis.