Angiomyolipoma overview

# 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.

# Historical Perspective
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.

# Classification
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.

# Pathophysiology
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.

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

# Differentiating Angiomyolipoma from other Diseases
Angiomyolipoma must be differentiated from retroperitoneal liposarcoma, adrenal myelolipoma, and renal cell carcinoma.

# Epidemiology and Demographics
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.

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

# Screening
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.

# Natural History, Complications and Prognosis
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.

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

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

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

# CT
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.

# MRI
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.

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

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

# Medical Therapy
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
- Size of the tumors
- Signs and symptoms
- Presence or absence of life threatening hemorrhage
- Its association with the tuberous sclerosis and
- The presence of the comorbidities.
Angiomyolipomas found incidentally,asymptomatic, 8cm), shown to progress to the development of the complication so treated electively.

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