Sclerosing angiomatoid nodular transformation (SANT): A rare splenic lesion

A 27-year-old male was referred to the radiology department for an abdominal ultrasound due to elevated liver enzymes in a blood work-up.

An abdominal ultrasound examination showed diffuse hepatic steatosis, which explained the altered levels of liver enzymes, and a slight enlargement of the spleen with a hypoechoic, heterogeneous, well-defined splenic lesion as an incidental finding (Figure 1).

To further characterise the splenic lesion, a contrast MRI was performed. An axial T2-weighted image demonstrated a 3.5 x 3.4 cm heterogeneous, predominantly hypointense, well-defined solitary mass with radiating bands (Figure 2). In a T1 sequence, the lesion appeared hypointense from its fibrous nature without loss of signal in out-of-phase due to an absence of microscopic fat (Figures 3a and 3b). In the dynamic study, it showed progressive contrast enhancement with a spoke-wheel pattern (Figures 4a, 4b and 4c). Diffusion-weighted imaging and ADC displayed the mass with lack of restriction (Figures 5a and 5b). These findings were compatible with a sclerosing angiomatoid nodular transformation of the spleen (SANT).

The spleen is the largest lymphatic intraperitoneal organ. It is composed of vascular tissue (red pulp) and lymphatic tissue (white pulp), which is why most splenic tumours are of vascular or lymphatic origin.

Most splenic lesions are benign; however, it is important to make a thorough differential diagnosis in order to detect characteristics of malignancy and aggressiveness. The first thing to consider is whether the tumour is solid or cystic, or if it is single or multiple.

In this case, there was a single, solid lesion, and therefore differential diagnoses must include vascular lesions such as haemangioma, hamartoma, SANT or angiosarcoma, as well as non-vascular lesions like lymphoma or inflammatory pseudotumour.

The imaging studies performed on the patient revealed a splenic mass exhibiting radiating bands and a spoked wheel pattern with progressive enhancement. Based on these findings, the following diagnoses were excluded: haemangioma, which is usually characterised by progressive homogeneous enhancement; hamartoma, which is characterised by early arterial enhancement; and angiosarcoma, which is characterised by heterogeneous enhancement, with a more aggressive behaviour and is associated with constitutional syndrome (such as fever, weight loss or fatigue).

The radiological findings of the mass were typical of sclerosing angiomatoid nodular transformation of the spleen (SANT).

SANT is a rare benign splenic lesion of vascular origin caused by an alteration of the red pulp and an exaggerated fibrous proliferation. On MRI, it appears as a typically low signal tumour on the T2 sequence with hypointense radiating bands extending to the centre of the mass that reflect fibrotic tissue. In the T1-weighted sequence, it may appear hypointense due to the presence of tissues with a high collagen density and low water content (fibrous nature). In the dynamic study it is characteristic that the radiant bands present progressive enhancement, being more intense in the later phases.

The final diagnosis is mainly histological, but since most lesions are asymptomatic or mild, such as splenomegaly, the lesion is not surgically resected and radiological follow-up is usually preferred.

In this clinical case, given that the patient was young and asymptomatic, and considering that the splenic lesion was identified incidentally, neither biopsy nor splenectomy was performed for histological confirmation. Instead, it was decided to monitor the patient and observe the lesion’s progression.

A follow-up liver MRI at 6 months confirmed the stability of the previously described splenic lesion (Figure 6).