Sclerosing Angiomatoid Nodular Transformation of the Spleen
Sclerosing angiomatoid nodular transformation (SANT) is a recently recognized nonneoplastic vascular lesion of the spleen with fewer than 30 cases described. Microscopically, SANT consists of multiple well-circumscribed vascular/ angiomatoid nodules showing plump endothelial cell and extravasated erythrocytes. The nodules are surrounded by a variable lymphoplasmacytic infiltrate, spindle cells, and collagenous stroma. The vascular nodules display a complex mixture of endothelial phenotypes resembling splenic sinusoids (CD34^sup -^/CD31^sup +^/CD8^sup +^), capillaries (CD34^sup +^/ CD31^sup +^/CD8^sup -^), and small veins (CD34^sup -^/CD31^sup +^/CD8^sup -^). Focal expression of CD68 can also be seen. The differential diagnosis of SANT includes splenic hamartoma, inflammatory myofibroblastic tumor, littoral cell angioma, and hemangioendothelioma. It has been postulated that SANT represents a peculiar hamartomatous transformation of splenic red pulp in response to an exaggerated nonneo-plastic stromal proliferation. SANT has a benign clinical course with splenectomy being curative.
Hemangiomas are the most common primary tumors of the spleen.1 Other rare vascular splenic lesions include lymphangioma,2 littoral cell angioma (LCA),3 he-mangioendothelioma, 4 and splenic hamartoma.5 In 2004 Martel et al6 described a distinctive nonneoplastic vascular lesion of the spleen, which they designated sclerosing an-giomatoid nodular transformation (SANT). Isolated examples of SANT had been previously described as splenic hamar-toma7 and hemangioendothelioma.8 In this review, we describe the clinical and pathologic features of SANT and discuss its major differential diagnoses.
Sclerosing angiomatoid nodular transformation is rare. In their original description, Martel et al6 reported 25 cases and another example was later added to the literature.9 Recently we have seen 2 cases affecting middle-aged women. The mean age at presentation is 53.7 years with a range from 22 to 74 years. Sclerosing angiomatoid nodular transformation shows a marked female predominance with a female-male ratio of 2:1.6,9 In the series by Martel et al,6 most patients were asymptomatic and the splenic mass was an incidental finding during laparotomy or during imaging studies for unrelated conditions. Some patients- approximately 16%-complained of abdominal pain or discomfort. A minority of patients presented with splenomegaly rarely associated with leukocytosis, poly-clonal gammopathy, and increased erythrocyte sedimentation rate.6 Reported concurrent diseases include hypertension, von Willebrand disease, chronic lymphocytic leukemia, and carcinomas of lung, gastrointestinal tract, and kidney with no metastasis to the spleen.6 The patient reported by Li et al9 had multiple medical problems including hypertension, diabetes mellitus, hypothyroidism, and prostate hyperplasia. Abdominal ultrasound, computed tomography scans, and magnetic resonance imaging studies usually reveal a hypodense, multinodular splenicmass. Computed tomography or magnetic resonance imaging with contrast cannot distinguish SANT from the surrounding spleen parenchyma.9 Splenectomy is usually performed on the discovery of a splenic mass and appears to be curative in all reported cases.
Although the histologic and immunohistochemical features of SANT have been characterized only recently by Martel et al,6 isolated cases were described as early as 19787 under the terms splenic hamartoma,5,7 cord-capillary hemangioma,10 multinodular hemangioma,11 and as a variant of splenic hemangioendothelioma.8 At low-power magnification, SANT is composed of multiple well-circumscribed individual and confluent vascular/angiomatoid nodules
with a variable fibrosclerotic stroma . The nodules are round to oval with variable sizes. Some are surrounded by dense concentric collagen fibers , whereas others show a fibrin rim resulting in a granuloma-like or necrotizing vasculitic appearance . Each nodule demonstrates a mixture of slit-like vascular spaces with a sievelike appearance lined by plump endothelial cells and pericytes admixed with ex-travasated red blood cells . The vessels incorporated in the nodules are highlighted by a reticulin stain . The endothelial cells show minimal cellular atypia, and only rare mitotic activity is seen within the nodules. The internodular stroma is fibromyxoid or sclerotic and contains variable numbers of myofibroblasts, plasma cells, lymphocytes, macrophages, and hemosiderin laden macrophages . The intercellular stro-ma may show large areas of hyalinization . The adjacent splenic tissue is usually compressed by the nodules but is otherwise within normal limits.