Sclerosing angiomatoid nodular transformation of the spleen
Sclerosing angiomatoid nodular transformation (SANT) of the spleen is a recently recognised, rare, non-neoplastic vascular splenic neoplasm of uncertain etiology. The term SANT first appeared in the literature in a 2004 paper by Martel et al. 3 which examined a series of 25 cases.
This relatively uncommon splenic lesion had however been recognised earlier by other authors under different names such as splenic hamartoma, cord capillary hemangioma, and multinodular haemangioma 4.
According to former studies it is most commonly encountered in middle-aged adults, with a mean age of presentation approximating 50 years with slight female preponderance 1,4, female-to-male ratio of 2:1 1,2.
A more recent review however (n= 97) showed, that 44.3% of reported case were male. Gender predilection is suspected to soon be neutralised as more cases are reported 4.
Majority of cases incidentally encountered during abdominal cross sectional imaging studies for other reasons.
The majority of lesions (approx. 80%) seem to be incidentally found on imaging.
When presenting with symptoms, abdominal pain predominates 1-4.
On macroscopy typically well-circumscribed mass of red-brown nodules, alternating with band-like stromal tissue, often forming a central stellate scar.
On microscopy nodular numerous erythrocytes, stromal components collagenous bands containing myofibroblasts, hemosiderin-laden macrophages, lymphocytes and plasma cells.
Immunohistochemically three distinct types:
- well-formed cord capillaries in an organised lobular arrangement that were CD34+/CD8−/CD31+
- vessels consistent with splenic sinusoids and CD34−/CD8+/CD31+
- small veins arranged in a very intricate mesh-like patterns, CD34−/CD8−/CD31+ 3,4
Typical pattern as a solitary, well-circumscribed splenic mass with smooth or lobular borders, variable in size.
Typically homogeneous on NECT, iso- to mild hypodensity compared to surrounding spleen.
After contrast administration most commonly comparatively hypovascular center with an enhancing rim and radiating vascularised tissue penetrating from the periphery toward the center of the lesion. Progressive central enhancement with delayed imaging, thought to be the result of contrast penetrating the center of the lesion from the vascular rim 1 - "spoke wheel" pattern.
Most commonly heterogeneous but low to intermediate signal intensity on T1-weighted imaging.
On T2-weighted sequences typically low signal - in contrast to most differential diagnosis as stated below.
Following intravenous gadolinium contrast, usually peripheral and septal enhancement in above mentioned “spoke wheel” pattern with central stellate scar hypoenhancing.
Few cases, 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 PET activity 4.
Scintigraphically cold, however this fairly unspecific sign will not aid in diagnosis. Absence of reticuloendothelial cells within the SANT lesion may account for this lack of uptake of 99mTc-sulfur colloid 1.
Treatment and prognosis
Treatment with splenectomy is curative and allows for histopathological characterisation, which appears to remain gold standard 4.
Diagnostic confidence and considerations
Published descriptions of cross-sectional imaging findings comprising above mentioned "spoke-wheel" appearance may suggest diagnosis. Nonetheless will concerns for malignancy and the potential for splenic rupture often render splenectomy the primary means of diagnosing splenic SANT 1.
The lesion is benign without risk of malignant transformation. Given the known, mostly asymptomatic character of this often incidental lesion - should an asymptomatic patient undergo an operative procedure?
As currently no sensitive and specific way exists to make a diagnosis of SANT without having a tissue sample, it may be prudent to remove the spleen even if SANT is suspected.
Although core biopsy is a sensitive and specific way to diagnose both haematologic and non-haematologic splenic lesions, the risk of intra-peritoneal seeding (if the lesion being biopsied proves to be malignant e.g. angiosarcoma) should be kept in mind 4.
For a differential of benign, indeterminate and malignant splenic lesions. See list of splenic lesions and anomalies.
Most of these demonstrate different signal intensities and/or more numerous lesions, possibly enabling differentiation from SANT.
- 1. Li L, Fisher DA, Stanek AE. Sclerosing angiomatoid nodular transformation (SANT) of the spleen: addition of a case with focal CD68 staining and distinctive CT features. Am. J. Surg. Pathol. 2005;29 (6): 839-41. Pubmed citation
- 2. Thacker C, Korn R, Millstine J et-al. Sclerosing angiomatoid nodular transformation of the spleen: CT, MR, PET, and ⁹⁹(m)Tc-sulfur colloid SPECT CT findings with gross and histopathological correlation. Abdom Imaging. 2011;35 (6): 683-9. doi:10.1007/s00261-009-9584-x - Free text at pubmed - Pubmed citation
- 3. Martel M, Cheuk W, Lombardi L et-al. Sclerosing angiomatoid nodular transformation (SANT): report of 25 cases of a distinctive benign splenic lesion. Am. J. Surg. Pathol. 2004;28 (10): 1268-79. Pubmed citation
- 4. Falk GA, Nooli NP, Morris-Stiff G et-al. Sclerosing Angiomatoid Nodular Transformation (SANT) of the spleen: Case report and review of the literature. Int J Surg Case Rep. 2012;3 (10): 492-500. doi:10.1016/j.ijscr.2012.06.003 - Free text at pubmed - Pubmed citation