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Diagnosis and Treatment of Renal Angiomyolipomas
Definition of Angiomyolipoma of the Kidney
Renal angiomyolipoma is a usually benign mesenchymal renal tumor in the family of perivascular epithelioid cell tumors (PEComas). It typically consists of adipose tissue, smooth muscle cells, and dysmorphic blood vessels. In addition to the classic fat-rich angiomyolipoma, fat-poor variants and the rare epithelioid angiomyolipoma—which may have malignant potential—occur (Restrepo et al., 2022).
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Epidemiology of Renal Angiomyolipoma
Prevalence:
The prevalence is 0.3 % in autopsy series and 0.1–0.4 % in ultrasound screening studies. Angiomyolipomas are substantially more common in women than in men. The peak age is 50–60 years.
Tuberous sclerosis:
45–80 % of patients with tuberous sclerosis have (bilateral) angiomyolipomas. In this patient group, men and women are affected equally, with a peak age of 30 years.
Etiology and Pathology of Angiomyolipoma
Etiology:
Angiomyolipomas arise from perivascular epithelioid cells. The TSC1/TSC2-mTOR signaling pathway is frequently involved in their pathogenesis. Hormonal influences, including hormone receptor expression, contribute to their higher prevalence in women and their growth during pregnancy.
Gross Pathology of Angiomyolipoma
Angiomyolipomas are gray-yellow lesions that lack a tumor capsule and are round to oval, bulging the renal capsule. Some show multicentric growth with lymph node involvement; this does not necessarily indicate metastatic disease.
Histology of Angiomyolipoma
Mature adipocytes, smooth muscle cells, and dysmorphic thick-walled blood vessels are characteristic of classic angiomyolipoma. Epithelioid morphology, marked atypia, necrosis, or increased mitotic activity suggests epithelioid angiomyolipoma with malignant potential.
Signs and Symptoms of Angiomyolipoma of the Kidney
- Most angiomyolipomas are asymptomatic and are detected incidentally on imaging.
- Flank pain and hematuria may occur.
- Wunderlich syndrome is a potentially life-threatening hemorrhage caused by spontaneous rupture into the retroperitoneum. The risk of bleeding increases with tumor size, intratumoral aneurysms, rapid growth, pregnancy, and tuberous sclerosis.
Diagnosis of Renal Angiomyolipoma
Renal Ultrasound
The high fat content of an angiomyolipoma produces a markedly echogenic renal mass. Fat-poor angiomyolipomas may have atypical mixed echogenicity. Small renal cell carcinomas can also appear echogenic, so ultrasound alone cannot reliably distinguish these lesions. A definitive diagnosis of classic angiomyolipoma requires detection of macroscopic fat by CT or MRI. For very small, sonographically typical echogenic lesions without risk factors, sonographic follow-up may be reasonable, provided the diagnosis is considered presumptive. See also renal ultrasound.
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Abdominal CT
Because of its fat content, angiomyolipoma typically appears as a hypodense renal mass measuring −20 to −80 HU, which can help distinguish it from renal cell carcinoma. Calcifications are uncommon in angiomyolipomas. Fat-poor and epithelioid angiomyolipomas may mimic renal cell carcinoma. See CT image and bilateral angiomyolipomas on CT.
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Abdominal MRI
MRI reliably detects macroscopic fat, which is typical of angiomyolipoma, and can help distinguish it from renal cell carcinoma. Chemical-shift sequences can also detect microscopic fat and may be helpful in evaluating fat-poor lesions.
Angiography
Neovascularization and intratumoral aneurysms may be present. Angiography is not useful for differential diagnosis but is performed before embolization.
Treatment of Renal Angiomyolipomas
Active Surveillance
Active surveillance is indicated for angiomyolipomas without a clinically relevant risk of bleeding or malignancy. The decision takes into account tumor size and growth, symptoms, intratumoral aneurysms, pregnancy plans, tuberous sclerosis, bilateral tumors, and the reliability of follow-up. Sporadic angiomyolipomas grow by less than 2 mm/year; growth is significantly faster in tuberous sclerosis. Clinical recommendations for imaging intervals in sporadic angiomyolipoma are limited: no regular follow-up for tumors smaller than 2 cm, imaging every five years for tumors measuring 2–3 cm, every two years for tumors measuring 3–4 cm, and annually for larger tumors. CT or MRI is used to establish the diagnosis and assess growth, symptoms, and bleeding risk (Chan et al., 2018). In tuberous sclerosis, MRI every 1–3 years is recommended, depending on the extent of angiomyolipoma involvement.
mTOR Inhibitors
Everolimus is approved to reduce tumor volume in progressive, multiple, or bilateral angiomyolipomas associated with tuberous sclerosis or sporadic lymphangioleiomyomatosis (Bissler et al., 2013). Its benefits and adverse effects should be weighed against those of the interventional options below.
Selective Embolization
Selective embolization is an important minimally invasive treatment option for acute bleeding and, electively, for symptomatic or bleeding-prone angiomyolipomas, particularly those with intratumoral aneurysms. Tumor volume decreases by an average of approximately 50 %. Complications include postembolization syndrome, incomplete tumor shrinkage, and recurrence requiring reintervention.
Partial Nephrectomy
Partial nephrectomy may be considered when the diagnosis is uncertain, epithelioid angiomyolipoma is suspected, or the tumor is in a location technically unfavorable for embolization. Surgery is used cautiously for angiomyolipomas that are clearly benign because embolization is less invasive.
Emergency Treatment of Retroperitoneal Hemorrhage
Initial management consists of hemodynamic stabilization, with blood transfusion as needed. Selective embolization is the preferred method of hemostasis. Surgical exploration of the kidney with partial nephrectomy or nephrectomy is reserved for severe bleeding that cannot be controlled or when interventional treatment is unavailable.
| Renal oncocytoma | Index | Other benign renal tumors |
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References
Bissler JJ, Kingswood JC, Radzikowska E, Zonnenberg BA, Frost M, Belousova E, Sauter M, Nonomura N, Brakemeier S, de Vries PJ, Whittemore VH, Chen D, Sahmoud T, Shah G, Lincy J, Lebwohl D, Budde K. Everolimus for angiomyolipoma associated with tuberous sclerosis complex or sporadic lymphangioleiomyomatosis (EXIST-2): a multicentre, randomised, double-blind, placebo-controlled trial. Lancet. 2013 Mar 9;381(9869):817-24. doi: 10.1016/S0140-6736(12)61767-X.
K. E. Chan, E. Chedgy, C. L. Bent, and K. J. Turner, “Surveillance imaging for sporadic renal angiomyolipoma less than 40 mm: lessons learnt and recommendations from the experience of a large district general hospital.,” Ann R Coll Surg Engl, vol. 100, no. 6, pp. 480–484, 2018, doi: 10.1308/rcsann.2018.0040.
Restrepo JCÁ, Millan DAC, Sabogal CAR, Bernal AFP, Donoso WD. New Trends and Evidence for the Management of Renal Angiomyolipoma: A Comprehensive Narrative Review of the Literature. J Kidney Cancer VHL. 2022 Jan 21;9(1):33-41. doi: 10.15586/jkcvhl.v9i1.177.
Deutsche Version: Angiomyolipom der Nieren
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