Thigh lesion, left, biopsy - Kaposiform hemangioendothelioma.
Kaposiform hemangioendothelioma is a locally aggressive vascular tumor with features of both capillary hemangioma and Kaposi sarcoma (Lyons, North et al. 2004). It occurs nearly exclusively in children. More than half of the cases present during the first year of life. Males are more often affected than females. Adult cases are rare (Mentzel, Mazzoleni et al. 1997). The etiology of kaposiform hemangioendothelioma remains unknown. It is not associated with HHV8 infection or Kaposi sarcoma. Tumors often involve soft tissue of extremities as ill-defined, violaceous lesions and may encase normal structures. They can also involve retroperitoneum, head and neck areas, mediastinum, bone, lymph nodes, and visceral organs (Tsang and Chan 1991). Large lesions at any site, especially retroperitoneal tumors, may present with thrombocytopenia and consumptive coagulopathy (Kasabach-Merritt phenomenon/syndrome) (Zukerberg, Nickoloff et al. 1993).
Histologically the tumor cells are monomorphic, grow in a multinodular pattern and form irregular lobules that infiltrate soft tissue in a "cannon ball" fashion. Mitotic activity is rare. Desmoplasia may be present, especially in deep lesions. Areas of slit-like vessels and large lymphatic channels are present at periphery of the lobules. The slit-like, spindled areas resemble Kaposi sarcoma. The lymphatic channels may be large and numerous, and qualified as lymphangioma/lymphangiomatosis. Glomeruloid cluster of vessels, which comprises tightly coiled, epithelioid, and CD31-positive capillaries with actin-positive pericytes, are characteristic of this lesion. The vessels in lobular, capillary hemangioma-like areas often contain fibrin thrombi and fragments of red blood cells (schistocytes). Hemosiderin deposition may be found.
Lymphatic markers (PROX1, LYVE1, podoplanin and VEGFR3) are positive in the slit-like, Kaposi-like areas. CD31, CD34 and FLI-1 are positive in the lobular and glomeruloid structures. Smooth muscle actin is positive in pericytes. GLUT-1, which is positive in infantile hemangioma, is negative in the endothelium of Kaposiform hemangioendothelioma.
The main differential diagnoses include infantile/juvenile hemangioma (proliferative phase), Kaposi sarcoma, acquired tufted angioma and spindle cell hemangioma. Infantile/juvenile hemangioma is a benign vascular lesion characterized in its proliferative phase by closely packed slit-like to wider capillary channels that may have a nodular configuration or may diffusely infiltrate the dermis/soft tissues. They are characteristically GLUT-1 positive besides showing endothelial markers CD31 and CD34. Kaposi sarcoma occurs in immunocompromised patients and older individuals. Microscopically, Kaposi sarcoma lacks capillary hemangioma-like areas and is positive for HHV8. Acquired tufted angioma occurs in the dermis and is morphologically indistinguishable from kaposiform hemangioendothelioma. The two lesions are best distinguished by clinical scenario. Acquired tufted angioma and kaposiform hemangioendothelioma have similar patient demographics and may represent different spectrum of the same disease entity. Spindle cell hemangioma occurs in distal extremities of adults and shows ectatic vessels, solid spindled cell areas, intravascular growth, and vacuolated endothelial cells ("blister cells").
Kaposiform hemangioendothelioma shows no tendency to spontaneously regress. Outcome depends on anatomical site, tumor extent, and severity of thrombocytopenia. Prognosis in patients with large or abdominal tumors is poor. Mortality is approximately 10% and is attributable to extensive local disease or Kasabach-Merritt phenomenon. Options of treatment include wide surgical excision and pharmacological approaches including vincristine, cyclophosphamide, methotrexate, actinomycin D and -interferon. Recurrence after wide local excision, if can be done, is rare. Rarely, regional lymph node metastasis can occur.
At the time of this report, the patient was followed conservatively with repeat MRI in 6 months due to stable tumor size and normal platelet levels. Blood work was followed every 2 months.
Lyons, L. L., P. E. North, et al. (2004). "Kaposiform hemangioendothelioma: a study of 33 cases emphasizing its pathologic, immunophenotypic, and biologic uniqueness from juvenile hemangioma." Am J Surg Pathol 28(5): 559-568.
Mentzel, T., G. Mazzoleni, et al. (1997). "Kaposiform hemangioendothelioma in adults. Clinicopathologic and immunohistochemical analysis of three cases." Am J Clin Pathol 108(4): 450-455.
Tsang, W. Y. and J. K. Chan (1991). "Kaposi-like infantile hemangioendothelioma. A distinctive vascular neoplasm of the retroperitoneum." Am J Surg Pathol 15(10): 982-989.
Zukerberg, L. R., B. J. Nickoloff, et al. (1993). "Kaposiform hemangioendothelioma of infancy and childhood. An aggressive neoplasm associated with Kasabach-Merritt syndrome and lymphangiomatosis." Am J Surg Pathol 17(4): 321-328.
WHO Classification of Tumours of Soft Tissue and Bone. Fourth Edition. 2013 Bone and Soft Tissue Pathology: A Volume in the High Yield Pathology Series. First Edition. 2012 Diagnostic Pathology: Soft Tissue Tumors. 2010
Contributed by Jason Chiang, MD, PhD and Sarangarajan Ranganathan, MD