Angiomyolipoma overview

Angiomyolipoma is a benign renal neoplasm previously considered to be a hamartoma or choristoma, but now known to be neoplastic. It is composed of variable amounts of fat, vascular, and smooth muscle elements. The fat density of the tumor on CT scan has been regarded to be pathognomonic. The lesion is well demarcated and contains mature elements. It occurs in more than 50% of individuals with tuberous sclerosis, often bilaterally. On gross pathology, well circumscribed and uniform yellow mass is characteristic finding of angiomyolipoma. Angiomyolipoma is caused by a defect in the TSC1 gene. Angiomyolipoma must be differentiated from retroperitoneal liposarcoma, adrenal myelolipoma, and renal cell carcinoma. If left untreated, small angiomyolipomas and those without dilated blood vessels (aneurysms) cause few symptoms. Small angiomyolipomas are associated with the most favorable prognosis. Common complications of angiomyolipoma include infection, hematuria and hemorrhage. Abdominal CT scan may be diagnostic for angiomyolipoma. On CT scan, angiomyolipoma is characterized by smooth tumor margin with low intratumoral fat component and homogenous enhancement on both corticomedullary and excretory phase scans. Surgery is not the first-line treatment option for patients with angiomyolipoma. Transcatheter arterial embolization is usually reserved for patients with complicated disease.

Angiomyolipoma was first described as a tumor in 1911 by Fisher. He also noted and described its association with the Tuberous Sclerosis. It has been named as Angiomyolipoma by Morgan and associates in 1951.

Angiomyolipoma may be classified according to radiologic appearance into 7 subtypes: classic angiomyolipoma, triphasic angiomyolipoma, fat poor angiomyolipoma, hyperattenuating angiomyolipoma, isoattenuating angiomyolipoma, angiomyolipoma with epithelial cysts, and angiomyolipoma in lymphangioleiomyomatosis.

On gross pathology, well circumscribed and uniform yellow mass is characteristic finding of angiomyolipoma. The components of an angiomyolipoma include vascular cells, immature smooth muscle cells and fat cells. Angiomyolipoma is caused by a defect in TSC1 gene. Diseases associated with angiomyolipoma include von Hippel-Lindau syndrome and tuberous sclerosis. Cytologic features of angiomyolipoma include round nuclei and bland chromatin. Immunohistochemistry markers of angiomyolipoma include positive melanocytic markers.

Angiomyolipoma is caused by a mutation in the TSC1 gene. It can also be caused by a defect in TSC2 gene.

Angiomyolipoma must be differentiated from retroperitoneal liposarcoma, adrenal myelolipoma, and renal cell carcinoma.

The incidence of angiomyolipoma is approximately 30 per 100,000 individuals worldwide. Females are more commonly affected with angiomyolipoma than males. Angiomyolipoma commonly affects individuals older than 40 years of age.

Tuberous sclerosis is a risk factor for the development of angiomyolipoma. Approximately 50% of individuals with tuberous sclerosis develop bilateral angiomyolipomas.

Patients who have tuberous sclerosis should be screened for angiomyolipoma. Abdominal CT scan is recommended for screening angiomyolipoma. High fat content is suggestive of angiomyolipoma.

If left untreated, small angiomyolipomas and those without dilated blood vessels (aneurysms) cause few symptoms. Small angiomyolipomas are associated with the most favorable prognosis. Common complications of angiomyolipoma include infection, hemorrhage, and shock.

Symptoms of angiomyolipoma include fever, nausea, vomiting, and abdominal pain.

Common physical examination findings of angiomyolipoma include fever, flank tenderness, and palpable mass.

Laboratory findings consistent with the diagnosis of angiomyolipoma include presence of red blood cells in urine and elevated white blood cell count.

Abdominal CT scan may be diagnostic for angiomyolipoma. On CT scan, angiomyolipoma is characterized by smooth tumor margin with low intratumoral fat component and homogenous enhancement on both corticomedullary and excretory phase scans.

Abdominal MRI may be diagnostic of angiomyolipoma. On MRI, angiomyolipoma is characterized by high signal intensity on non-fat saturated sequences and loss of signal following fat saturation.

On abdominal ultrasound, angiomyolipoma is characterized by hyperechoic lesions and posterior acoustic shadowing in the cortex.

On digital subtraction angiography, angiolipoma is characterized by hypervascular lesions, microvascular aneurysms and absent AV shunting.

Treatment options include selective renal artery embolization,nephron sparing surgery( enucleation or partial nephrectomy), complete and radical nephrectomy, radio-frequency ablation and everolimus. Treatment and management of the Angiomyolipoma depends largely on

1. Size of the tumors
2. Signs and symptoms
3. Presence or absence of life threatening hemorrhage
4. Its association with the tuberous sclerosis and
5. The presence of the comorbidities.

Angiomyolipomas found incidentally,asymptomatic, < 4 cm in size, generally requires no intervention beside periodic evaluation. Medium sized lesion(4-8 cm) should be closely followed with the serial imaging studies(every 6 month and then yearly once stable) and elective intervention provided if the change in the size or symptoms noticed, to increases the chances of renal function salvage. Larger lesion(>8cm), shown to progress to the development of the complication so treated electively.

Surgery is not the first-line treatment option for patients with angiomyolipoma. Transcatheter arterial embolization is usually reserved for patients with complicated disease.

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