Encyclopedia of Pathology

Living Edition
| Editors: J.H.J.M. van Krieken

Angiomyolipoma

  • Anna Caliò
  • Diego Segala
  • Guido MartignoniEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-28845-1_3777-1

Definition

Angiomyolipoma is the most common mesenchymal neoplasm of the kidney, classically composed by a variable mixture of adipocytes, smooth muscle cells, and abnormal thick-wall blood vessels. The perivascular epithelioid cell is considered to be the cell of origin for this and other related tumors.

Clinical Features

Angiomyolipoma is a benign neoplasm and can be sporadic or occurs in patients with tuberous sclerosis (Eble 1998).
  • Incidence

    Angiomyolipoma accounts for approximately 1% of surgically removed renal tumors.

  • Age

    Sporadic angiomyolipoma occurs in the fourth to sixth decades of life, whereas tuberous sclerosis in the third and fourth decades of life.

  • Sex

    Sporadic angiomyolipoma has a female predominance; in patients with tuberous sclerosis, there is no gender predilection.

  • Site

    There is no site predilection in the sporadic angiomyolipoma, whereas those occurring in patients with tuberous sclerosis are usually bilateral, small, and multifocal.

  • Treatment

    Partial nephrectomy and less frequently, radical nephrectomy is the standard treatment.

  • Outcome

    Angiomyolipoma is a benign neoplasm. Multifocality and regional lymph node involvement can occur, especially in patients with tuberous sclerosis, and the latter finding is considered to represent a multifocal growth pattern rather than metastasis.

Macroscopy

Angiomyolipomas usually are well demarcated, but not encapsulated. The color ranges from yellow to pink-tan, depending on the relative proportions of the various tissue components. Prominent cystic or pseudocystic changes may very rarely be present.

Microscopy

Angiomyolipoma contains more than one cell type (Fig. 1), but occasionally adipocytes (lipoma-like angiomyolipoma) or spindle smooth muscle cells (leiomyoma-like angiomyolipoma) predominate in particular lesions. Microscopic angiomyolipomas (so called microhamartomas) are small nodules often present in the renal parenchyma bearing angiomyolipomas. Intraglomerular lesions with features overlapping with those of angiomyolipoma mainly occur in patients with tuberous sclerosis and in the TSC2/PKD1 contiguous gene syndrome, a disease with a deletion disrupting both TSC2 and PKD1 (autosomal dominant polycystic disease gene). Cystic angiomyolipoma (angiomyolipoma with epithelial cysts) is a rare variant of angiomyolipoma with solid (muscle-predominant) and cystic components (epithelial cysts with a subepithelial “cambium-like” layer of stromal cells) (Martignoni et al. 2015).
Fig. 1

Classic angiomyolipoma composed by adipocytes, smooth muscle cells, and abnormal thick-wall blood vessels

Immunophenotype

Angiomyolipoma is characterized by a coexpression of melanocytic markers (HMB45, Mart1/Melan-A, and microphthalmia transcription factor) (Pea et al. 1991), cathepsin K, and smooth muscle markers (smooth muscle actin, muscle-specific actin, and calponin) (Martignoni et al. 2012). Staining for CD68, S-100 protein, estrogen and progesterone receptors, and desmin may also be present, whereas epithelial markers are always negative.

Molecular Features

The alterations of two genes are known to cause tuberous sclerosis. The TSC1 gene is located on chromosome 9q34 and encodes hamartin; the TSC2 gene is located on chromosome 16p13 and encodes tuberin. These two proteins interact with each other, forming a cytoplasmic complex. Angiomyolipoma frequently shows loss of heterozygosity (LOH) of variable portions of TSC2 gene locus and less frequently TSC1 gene locus in both sporadic and inherited tumors. Recently, TSC2 mutation but not TSC1 mutation has been reported in sporadic angiomyolipoma (Qin et al. 2011).

Differential Diagnosis

Tumors prevalently composed by smooth muscle cells and adipocytes may mimic a leiomyoma/leiomyosarcoma and lipoma/liposarcoma, respectively. The expression of melanocytic markers is extremely useful for the diagnosis.

References and Further Reading

  1. Eble, J. N. (1998). Angiomyolipoma of kidney. Seminars in Diagnostic Pathology, 15, 21–40.PubMedGoogle Scholar
  2. Martignoni, G., Bonetti, F., Chilosi, M., et al. (2012). Cathepsin K expression in the spectrum of perivascular epithelioid cell (PEC) lesions of the kidney. Modern Pathology, 25, 100–111.CrossRefGoogle Scholar
  3. Martignoni, G., Pea, M., Zampini, C., et al. (2015). PEComas of the kidney and of the genitourinary tract. Seminars in Diagnostic Pathology, 32, 140–159.CrossRefGoogle Scholar
  4. Pea, M., Bonetti, F., Zamboni, G., et al. (1991). Melanocyte-marker-HMB-45 is regularly expressed in angiomyolipoma of the kidney. Pathology, 23, 185–188.CrossRefGoogle Scholar
  5. Qin, W., Bajaj, V., Malinowska, I., et al. (2011). Angiomyolipoma have common mutations in TSC2 but no other common genetic events. PLoS One, 6, e24919.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Diagnostic and Public Health, Section of PathologyUniversity of VeronaVeronaItaly
  2. 2.Department of PathologyPederzoli HospitalPeschiera del GardaItaly