Sclerosing angiomatoid nodular transformation of the spleen mimicking metastasis of melanoma: a case report and review of the literature

BACKGROUND Sclerosing angiomatoid nodular transformation is a benign disorder of splenic tissue and is often mistaken as a potentially malignant entity in the diagnostic process. To the best of our knowledge, this is the first report of sclerosing angiomatoid nodular transformation mimicking metastasis of melanoma in the literature. CASE PRESENTATION A 43-year-old white man presented with a newly found splenic mass 4 years ago to our Department of Gastroenterology. He was diagnosed as having a superficial spreading malignant melanoma localized at his left instep 7 years ago and was successfully treated with radical local resection. Several diagnostic procedures were conducted. Ultrasound showed a hypoechoic lesion in the inferior pole of his spleen with a diameter of 2 cm, blurred boundaries, and inhomogeneous interior pattern. Contrast-enhanced ultrasound was inconclusive and showed only discrete contrast enhancement of the lesion with accentuated nodule-like enrichment of the boundaries in the arterial phase. Computed tomography and magnetic resonance imaging scans showed two splenic lesions which were highly suspicious of metastasis. Magnetic resonance imaging of his head was inconspicuous. Bone scintigraphy showed no abnormal results. Fine-needle aspiration indicated metastasis of the above-mentioned malignant melanoma. We conducted a laparoscopic splenectomy. His intraoperative and postoperative course were uneventful. In contrast to the result of the fine-needle aspiration, the presence of metastasis of melanoma could not be confirmed. Histological analysis revealed nodule-like arrangement of fibroblasts with low cell density and a predominance of dilated capillaries, indicating sclerosing angiomatoid nodular transformation of the spleen. CONCLUSIONS There are no preoperative diagnostic imaging procedures which can definitely differentiate sclerosing angiomatoid nodular transformation from malignancies in cases of morphological and immunophenotypic variations of the specimen. Morphological and immunophenotypic variations of the specimen represent a diagnostic challenge and can mimic malignoma. As reported in our case, the specimen obtained by ultrasound-guided fine-needle aspiration led to the diagnosis of metastasis of melanoma. Splenectomy is often conducted due to a splenic mass suspicious of malignoma as described in our case or with unknown valency in different diagnostic imaging procedures.