Fat-containing Lesions of the Retroperitoneum: Radiologic-Pathologic Correlation

Abstract

Retroperitoneal lesions represent a broad, diverse collection of entities; when they contain fat, the differential diagnosis, which ranges from benign to fully malignant lesions, substantially narrows. Lipomas rarely occur in the retroperitoneum; thus, fat-containing lesions in this location should never be dismissed as lipoma. Pelvic lipomatosis is the overgrowth of histologically normal fat in the extraabdominal compartments of the pelvis along the perirectal and perivesicular spaces. Infants and young children develop lipoblastomas rather than liposarcomas, which occur in older patients. Liposarcomas typically occur in patients 50-70 years old and manifest in multiple subtypes, with the most common being well-differentiated liposarcoma. Liposarcomas are histologically and radiologically protean, with no one imaging feature specific across the spectrum of subtypes. Hibernoma is a rare benign soft-tissue tumor composed of brown fat. Because hibernomas contain varied portions of brown and white fat as well as lesser amounts of myxoid material and spindle cells, their imaging features vary considerably. Teratomas are neoplasms that originate in pluripotent cells--benign or malignant germ cells--that give rise to a wide spectrum of mature or immature tissues that are foreign to the location in which they arise and which demonstrate varying amounts of organ formation. Myelolipoma, a benign tumor composed of mature fat and interspersed hematopoietic elements that resemble bone marrow, typically originate in an otherwise normal adrenal gland. Angiomyolipoma is composed of varying admixtures of blood vessels, smooth muscle cells, and adipose tissue; any one or two of these elements may predominate. Although these fat-containing lesions have overlapping radiologic features, use of demographic and clinical data helps refine the diagnostic options and treatment.

A case report of lipoma-like hibernoma in axilla: A rarely benign tumor of brown adipose tissue

“…[2,17] This brown adipose tissue has smaller cells of different size, with a multilocular appearance; and the greater number of mitochondria present in brown fat is related to the exothermic function, which constitutes a unique property of brown adipose tissue. [15,18] Also, the connective tissue surrounding these cells has abundant blood supply, which gives hypervascular characteristics in imaging studies. [10,11] Lipoma-like hibernoma only have a few multilocular cells and can be wrongly classified as liposarcoma.…”

“…Welldifferentiated liposarcoma resembles it on low-power examination, but closer inspection shows scattered tumor cells with large, deep-staining nuclei. [20] Due to this it is especially important to perform a differential diagnosis with lipoma, fibroma, neurofibroma, angiolipoma, and even with liposarcoma, by clinically and radiologically studies, making a differential diagnoses with myxoid liposacorm, angiomyolipoma and mesenteric panniculitis; [12] so myxoid liposarcoma may present a clinical picture and radiological findings similar to hibernoma and lipoblastoma, but it is associated with infiltrating growth, presenting cellular atypia and is extremely infrequent in the pediatric age; [20] the angiomyolipoma is a vascular tumour with striated muscle cells and adipose tissue, [18,21] and characteristically found at the renal level.…”

Renal angiomyolipomas in tuberous sclerosis

“…Classical findings include the triad of adenoma sebaceum, seizures, and mental retardation. The inheritance is autosomal dominant; however, spontaneous mutation is described up to 66 % [1][2][3][4][5][6][7][8][9].…”

“…Angiomyolipomas usually are asymptomatic, when they are detected. However, follow-up, especially in case of large tumors, is obligatory due to the risk of rupture with consecutive bleeding [3,6]. In patients with tuberous sclerosis bilateral angiomyolipomas of the kidneys are found frequently (55-75%) [1].…”

Hibernoma: tumor retroperitoneal de grasa parda. Informe de un caso pediátrico

“…8 El angiomiolipoma, es un tumor compuesto por estructuras vasculares, células de músculo estriado y tejido adiposo. 12,13 Se encuentran característicamente a nivel renal. En raras ocasiones, tienen crecimiento extrarrenal y se manifiestan en retroperitoneo, órganos sólidos, cuello y región pélvica.…”