Renal angiomyolipomas from patients with sporadic lymphangiomyomatosis contain both neoplastic and non-neoplastic vascular structures

Abstract

Renal angiomyolipomas are highly vascular tumors that occur sporadically, in women with pulmonary lymphangiomyomatosis (LAM), and in tuberous sclerosis complex (TSC). The goal of this study was to determine whether the distinctive vessels of angiomyolipomas are neoplastic or reactive. We studied angiomyolipomas with loss of heterozygosity (LOH) in the TSC2 region of chromosome 16p13 from patients with LAM. We found that angiomyolipomas contain five morphologically distinct vessel types: cellular, collagenous, hemangiopericytic, glomeruloid, and aneurysmatic. Using laser capture microdissection, we determined that four of the vessel types have TSC2 LOH and are therefore neoplastic. One vessel type, collagenous vessels, did not have LOH, and is presumably reactive. Recently, activation of S6 Kinase and its target S6 ribosomal protein (S6) was demonstrated in cells lacking TSC2 expression. We found that angiomyolipoma vessel types in which LOH were detected were immunoreactive with anti-phospho-S6 antibodies. Angiomyolipoma cells without LOH, including the endothelial component of the vessels, were not immunoreactive. To our knowledge, angiomyolipomas are the first benign vascular tumor in which the vascular cells, rather than the stromal cells, have been found to be neoplastic. Angiomyolipomas appear to reflect novel vascular mechanisms that may be the result of activation of cellular pathways involving S6 Kinase.

Figure 1.

Angiomyolipomas contain five morphological vessel types. Cellular vessels (A, magnification, ×400) and collagenous vessels (B, magnification, ×400) have thick walls and similar lumen sizes, but the wall of cellular vessels is highly cellular while the wall of collagenous vessels is hypocellular. Hemangiopericytic vessels (C, magnification, ×400) have a thin wall and branching or irregularly shaped lumen. Glomeruloid vessels (D, magnification, ×400) have cellular walls with a clustered appearance and small lumens. Aneurysmatic vessels (E, magnification, ×400) have irregular hypocellular walls, often with aneurysm-like dilatations. In each panel, the wall thickness of the vessel is indicated.

Figure 2.

Histochemical and immunohistochemical differences between cellular and collagenous vessels. Collagenous vessels frequently contained scattered, irregularly positioned larger cells, indicated with an arrow (A, magnification, ×400, B, magnification, ×1000). Masson trichrome staining demonstrates that collagenous vessels have abundant collagen deposition (C, magnification, ×200) while cellular vessels have little extracellular collagen (D, magnification, ×100). Desmin immunoreactivity was absent in the walls of collagenous vessels (E, magnification, ×400) but strongly positive in cellular vessels (F, magnification, ×400).

Figure 3.

Immunohistochemical features of the different vessel types. Vimentin and smooth muscle actin reactivity was present in cellular (A and B, magnification, ×100), collagenous (D and E, magnification, ×100), hemangiopericytic (G and H, magnification, ×200), glomeruloid (J and K, magnification, ×200) and aneurysmatic vessels (M and N, magnification, ×100). Desmin reactivity was present only in cellular (C, magnification, ×100) and hemangiopericytic vessels(I, magnification, ×200). Negative desmin reactivity was observed in collagenous (F, magnification, ×100), glomeruloid (L, magnification, ×200) and aneurysmatic vessels (O, magnification, ×100).

Figure 4.

LOH is present in four of the five angiomyolipoma vessel types. Examples of chromosome 16p13 LOH analyses are shown for each of the different vessel types. Beneath each panel, the patient number and marker are provided. The location of the primary band representing each of the two alleles is indicated with a line in the normal kidney (NK). The “lost” allele is indicated with an arrow in non-microdissected angiomyolipoma (A). LOH was seen in the microdissected angiomyolipoma smooth muscle cell component (SM) and fat component (F), and in cellular vessels (CeV), hemangiopericytic vessels (HV), aneurysmatic vessels (AV), and glomeruloid vessels (GV). LOH was not detected in normal kidney (NK) or in collagenous vessels (CoV).

Figure 5.

Angiomyolipoma endothelial cells do not have LOH. The location of the primary band representing each of the two alleles is indicated with a line in the normal kidney (NK). The “lost” allele is indicated with an arrow in non-microdissected angiomyolipoma (AML). LOH was not detected in microdissected endothelial cells from cellular vessels (CeV), aneurysmatic vessels (AV), or collagenous vessels (CoV).

Figure 6.

Hyperphosphorylation of S6 ribosomal protein is present in the neoplastic components of the angiomyolipomas. Phospho-S6 ribosomal protein immunoreactivity was present in the angiomyolipoma fat component (A, magnification, ×400, arrowheads), in the smooth muscle component (B, asterisk, magnification, ×400), and in cells in the walls of cellular vessels (B, magnification, ×400), hemangiopericytic vessels (D, magnification, ×400), glomeruloid vessels (E, magnification, ×400), and aneurysmatic vessels (F, magnification, ×400), but not in the walls of collagenous vessels (C, magnification, ×400). Endothelial cells (arrows in panels B, C, D, E, and F) were not immunoreactive. In each panel, the wall thickness of the vessel is indicated.