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Angiomyolipoma of the Kidney

Definition of Angiomyolipoma of the Kidney

Angiomyolipoma of the kidney is a rare benign renal tumor with a high fat content (Oesterling et al, 1986) (Nelson et al, 2002).

Epidemiology of Renal Angiomyolipoma

Prevalence:

The prevalence in autopsies is 0.3%, with ultrasound screening 0.1%. Women are much more frequently affected than men. Age peak 50–60 years.

Tuberous sclerosis:

45–80% of patients with tuberous sclerosis have (bilateral) asymptomatic angiomyolipomas. In tuberous sclerosis, there is an equal distribution between men and women, age peak 30 years.

Etiology and Pathology of Angiomyolipoma

Etiology:

Angiomyolipomas derive from perivascular epithelioid cells and grow probably hormone-dependent.

Gross Pathology of Angiomyolipoma:

Angiomyolipomas are grey-yellow lesions without a tumor capsule, round to oval. Sometimes, angiomyolipomas show multi-center growth with involvement of lymph nodes without metastatic potential.

Histology of Angiomyolipoma:

Mature fat cells, smooth muscle cells, (atypical) blood vessels, occasional mitoses.

Signs and Symptoms of Angiomyolipoma of the Kidney

• Flank pain
• Potentially life-threatening hemorrhage due to spontaneous rupture into the retroperitoneum (Wunderlich's syndrome). Pregnancy increases the risk of rupture.

Diagnosis of Renal Angiomyolipoma

Sonography of the Kidney:

Sonography of the kidneys shows an echogenic mass in the kidney, caused by the high fat content. Since all other kidney tumors generate hypoechoic to isoechogenic lesions, it is possible to differentiate angiomyolipoma from other kidney tumors by sonography.

CT-Abdomen:

The fat content typically causes a hypodense mass in the kidney with -20 to -80 HU, this enables the differentiation to renal cell carcinoma [fig. CT of angiomyolipoma]. Calcifications are rare in renal angiomyolipoma.

Fig. CT abdomen of renal angiomyolipoma: visible are hypodense fatty portions of the kidney tumor. With kind permission of Dr. G. Antes, Kempten.

MRI Abdomen:

MRI enables the reliable detection of fat, which is typical for angiomyolipoma, and allows the differentiation to a renal cell carcinoma.

Angiography:

Neovascularization, similar to renal cell carcinoma, are possible. Angiography has no role in the differential diagnosis of renal tumors anymore.

Treatment of Renal Angiomyolipomas

Conservative Treatment of Angiomyolipomas:

Annual imaging controls are possible with angiomyolipomas less than 4 cm and mild symptoms. The annual growth rate of sporadic angiomyolipoma is less than 2 mm/year, but significant higher in tuberous sclerosis (Chan et al, 2018).

Partial Nephrectomy:

Partial nephrectomy is indicated in angiomyolipomas of >4 cm, severe symptoms or in tumors of uncertain diagnosis.

Selective embolization:

Selective embolization is a possible minimally invasive treatment option. Sometimes, a relapse is possible after embolization. Rarely, percutaneous drainage of necrosis is necessary.

Emergency nephrectomy:

Nephrectomy is necessary in rupture of angiomyolipoma with life-threatening bleeding.

References

Nelson, C. P. & Sanda, M. G.

Contemporary diagnosis and management of renal angiomyolipoma.
J Urol, 2002, 168, 1315-1325

Oesterling u.a. 1986 OESTERLING, J. E. ; FISHMAN, E. K. ; GOLDMAN, S. M. ; MARSHALL, F. F.:

The management of renal angiomyolipoma.
In: J Urol
135 (1986), Nr. 6, S. 1121–4

  Deutsche Version: Angiomyolipom der Nieren