Sclerosing angiomatoid nodular transformation of the spleen

Last revised by Arlene Campos on 3 May 2024

Sclerosing angiomatoid nodular transformation (SANT) of the spleen is a rare, non-neoplastic vascular splenic lesion of uncertain etiology. 

The term SANT first appeared in the literature in a 2004 article by Martel et al. which examined a series of 25 cases 3. This relatively uncommon splenic lesion had however been recognized earlier by other authors under different names such as splenic hamartoma, cord capillary hemangioma, and multinodular hemangioma 4.

According to older studies, it is most commonly encountered in middle-aged adults, with a mean age of presentation ~50 years and a female to male ratio of 2:1 1,2,4. A review, however, showed that 44.3% of the reported cases were male. As more cases are reported it is expected that this apparent gender bias will disappear 4.

The majority of cases are incidentalomas. When presenting with symptoms, abdominal pain predominates 1-4. Clinically, it may manifest with splenomegaly and pancytopenia.  

On microscopy, it is typically a well-circumscribed mass of red-brown nodules, alternating with band-like stromal tissue, often forming a central fibrous stellate scar.

Histology shows numerous nodular erythrocytes, stromal components collagenous bands containing myofibroblasts, hemosiderin-laden macrophages, lymphocytes and plasma cells.

Immunohistochemically, there are three distinct types:

  1. well-formed cord capillaries in an organized lobular arrangement that are CD34+/CD8−/CD31+

  2. vessels consistent with splenic sinusoids and CD34−/CD8+/CD31+

  3. small veins arranged in a very intricate mesh-like pattern, CD34−/CD8−/CD31+ 3,4

Usually characterized as a well-circumscribed hypoechogenic mass 5

It commonly presents as a solitary and well-circumscribed splenic mass with smooth or lobular borders, and is variable in size.

On non-contrast CT, it is homogeneous and iso- to mildly hypodense compared to the surrounding spleen.

On post-contrast phases, it demonstrates a comparatively hypovascular center with an enhancing rim and radiating vascularized tissue penetrating from the periphery toward the center of the lesion 5. Progressive central enhancement with delayed imaging is thought to be the result of contrast penetrating the center of the lesion from the vascular rim, described as a "spoke wheel" pattern 1.

  • T1: most commonly heterogeneous but low to intermediate signal intensity

  • T2: typically low signal (in contrast to most of the differential diagnoses stated below)

  • T1 C+ (Gd): usually peripheral and septal enhancement in a “spoke wheel” pattern with a central hypoenhancing stellate scar

May be slightly hypermetabolic with increased SUV measurements compared to hepatic and surrounding normal splenic uptake. Abundance of cells, including hemosiderin-laden macrophages, myofibroblasts, lymphocytes, and plasma cells as aforementioned, may account for splenic SANT’s FDG avidity 1. However, other authors have reported SANT cases without FDG-PET activity 4.

SANT is scintigraphically cold, however, this fairly non-specific sign will not aid in diagnosis. The absence of reticuloendothelial cells within the SANT lesion may account for this lack of uptake of 99mTc-sulfur colloid 1.

The lesion is benign without risk of malignant transformation. Treatment with splenectomy allows for histopathological characterization, which is the gold standard 4.

Although core biopsy is a sensitive and specific way to diagnose both hematologic and non-hematologic splenic lesions, the risk of intraperitoneal seeding (if the lesion is biopsied and proves to be malignant e.g. angiosarcoma) should be kept in mind 4.

For a differential of benign, indeterminate, and malignant splenic lesions, see the list of splenic lesions and anomalies.

Most of these demonstrate different signal intensities and/or more numerous lesions, potentially enabling differentiation from SANT.

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