Sclerosing angiomatoid nodular transformation of the spleen
Sclerosing angiomatoid nodular transformation (SANT) of the spleen is a recently recognized, rare, non-neoplastic vascular splenic lesion of uncertain etiology.
The term SANT first appeared in the literature in a 2004 paper 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 with a female-to-male ratio of 2:1 1,2,4.
A more recent review (n= 97), 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:
- well-formed cord capillaries in an organized lobular arrangement that are CD34+/CD8−/CD31+
- vessels consistent with splenic sinusoids and CD34−/CD8+/CD31+
- small veins arranged in a very intricate mesh-like pattern, CD34−/CD8−/CD31+ 3,4
Usually characterized as a well-circumscribed hypoechogenic mass 5.
Common presenting as a solitary and well-circumscribed splenic mass with smooth or lobular borders, variable in size.
- NECT: homogeneous, iso- to mild hypodensity compared to surrounding spleen
- post-contrast phases: 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 thought to be the result of contrast penetrating the center of the lesion from the vascular rim 1 - "spoke wheel" pattern
- T1: most commonly heterogeneous but low to an 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 above mentioned “spoke wheel” pattern with a central hypoenhancing stellate scar
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 FDG-PET activity 4.
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.
Treatment and prognosis
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.
- 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
- 5. Lee HJ, Kim JW, Hong JH et-al. Cross-sectional Imaging of Splenic Lesions: RadioGraphics Fundamentals | Online Presentation. (2018) Radiographics : a review publication of the Radiological Society of North America, Inc. 38 (2): 435-436. doi:10.1148/rg.2018170119 - Pubmed
- 6. Rachel B. Lewis, Grant E. Lattin, Meenakshi Nandedkar et-al. Sclerosing Angiomatoid Nodular Transformation of the Spleen: CT and MRI Features With Pathologic Correlation. (2013) American Journal of Roentgenology. 200 (4): W353-60. doi:10.2214/AJR.12.9522 - Pubmed
- 7. Ahlam A. Awamleh and Bayardo Perez-Ordoñez (2007) Sclerosing Angiomatoid Nodular Transformation of the Spleen. Archives of Pathology & Laboratory Medicine: June 2007, Vol. 131, No. 6, pp. 974-978. doi:10.1043/1543-2165(2007)131[974:SANTOT]2.0.CO;2
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