Sclerosing angiomatoid nodular transformation of the spleen: clinical, computed tomography, and magnetic resonance imaging characteristics.

Background: Sclerosing angiomatoid nodular transformation (SANT) of the spleen is a benign, vasculogenic lesion with unclear etiology. Despite increased recognition of its imaging features, the rates of imaging misinterpretation and unnecessary surgery for SANT remain high, and a possible association with benign and malignant tumors have been suggested. This study aimed to systematically analyze the clinical and imaging characteristics of SANT to improve clinician and radiologist knowledge, reduce overtreatment, and increase the awareness of potential concomitant diseases in other organs.

Methods: A retrospective cohort study consecutively sampled medical records from The First Affiliated Hospital, Zhejiang University School of Medicine between January 2012 and June 2024, ultimately 40 patients with pathologically confirmed SANT of the spleen were enrolled. Among them, 16 underwent both enhanced computed tomography (CT) and magnetic resonance imaging (MRI) scans, 8 underwent only enhanced MRI scans, and 16 underwent only enhanced CT scans. We analyzed the clinical characteristics, CT, and MRI features of these patients.

Results: Among the 40 patients with SANT, there were 21 males and 19 females, with an age range of 18-71 years, an average age of 42.3±14.6 years, and a median age of 40.5 years. Additionally, 90% (36/40) had solitary lesions, while 10% (4/40) had multiple lesions; 47.5% (19/40) cases of SANT were detected via routine health checks, and 52.5% (21/40) were found incidentally during other investigations; 30% (12/40) cases were correctly identified as SANT by preoperative imaging diagnosis, whereas 70% (28/40) cases were misdiagnosed prior to surgery. All lesions had an oval shape, among which 65% (26/40) had well-defined margins, 27.5% (11/40) had partially clear boundaries, and 7.5% (3/40) had ill-defined borders. Calcification was observed in 15.6% (5/32) cases by CT examinations. Twenty-four out of 24 (100%) displayed low-signal scars on T2-weighted imaging (T2WI), with all of these scars showing enhancement, and 70.8% (17/24) cases exhibited signals indicative of hemosiderin. After contrast enhancement, 65% (26/40) cases showed a "spoke-wheel" pattern of enhancement, while 35% (14/40) cases exhibited nodular enhancement. In 40% (16/40) cases, branches of the splenic artery traversing the lesions were visible. Progressive enhancement was the predominant pattern observed 92.5% (37/40).

Conclusions: The main imaging features of SANT, a rare, benign primary splenic lesion of unknown etiology, include solitary, solid masses with a rounded shape, mostly well-defined margins, slightly lower density than the spleen on noncontrast CT, occasional calcification, and predominantly iso-to-low-signal intensity on MRI with an even lower-signal scars on T2WI. SANT exhibits a typical progressive enhancement pattern with delayed central scar enhancement, characterized by the typical spoke-wheel pattern.