Angiomyolipoma

Renal angiomyolipomas are the most prevalent benign renal tumour. (1)

• in the majority of cases the angiomyolipoma is asymptomatic. However it may present as an abdominal mass or with haematuria. The likelihood of an angiomyolipoma being symptomatic is higher with tumours greater than 4cm in diameter
• it occurs in more than 50% of individuals with tuberous sclerosis. It also occurs sporadically and it is four times more common in women
• they are rare kidney tumours that account for only 0.3% to 3% of all renal neoplasms (2)
• their overall prevalence rate ranges from 0.13% to 2.2%, with 80% of cases being sporadic. The remaining 20% are associated with pulmonary lymphangioleiomyomatosis or tuberous sclerosis complex (3)

The tumour is composed of fat, blood vessels and smooth muscle. The fat has a characteristic tissue density that often permits easy identification of an angiomyolipoma on CT.

The majority of tumours can be managed conservatively, especially if they are asymptomatic. Medical therapy of angiomyolipomas is preferred over surgical management, whenever possible, to preserve renal function. (4)

Hereditary renal angiomyolipomas, linked with conditions such as tuberous sclerosis or pulmonary lymphangioleiomyomatosis, stem from mutations in the TSC1 or TSC2 genes, leading to uncontrolled activation of the mTOR pathway. This results in cell overgrowth and the formation of angiomyolipomas. Medications that inhibit the mTOR pathway can interrupt tumour progression and promote the reversion of the existing lesions.(5)

The introduction of sirolimus marked the inception of mTOR inhibitor therapy used to treat hereditary angiomyolipomas. (6)

Everolimus is an mTOR inhibitor approved for treating hereditary angiomyolipomas in tuberous sclerosis complex cases and has been reported to reduce tumour size by an average of 55%. (7)The standard starting dosage of everolimus is 10 mg daily and continued efficacy has been reported, even after 4 years of treatment. (8)

In some cases where the diagnosis is not established with imaging findings, partial nephrectomy enables pathologic diagnosis with a minimal loss of function. Resection of the tumour may be necessary for the relief of pain or haemorrhage. Radical nephrectomy may also be indicated in acute severe presentations e.g. massive haemorrhage. (9)

Currently, selective renal artery embolization is considered the first-line treatment for angiomyolipoma, particularly in cases at risk of acute bleeding, active haemorrhaging, or hemodynamic instability. (10)

There have been reports of malignant change in angiomyolipoma in patients without tuberous sclerosis although this appears a rare occurrence and only the subject of case reports. (5)

Reference

1. Hatano T, Egawa S. Renal angiomyolipoma with tuberous sclerosis complex: How it differs from sporadic angiomyolipoma in both management and care. Asian J Surg. 2020 Oct;43(10):967-972
2. Nelson CP, Sanda MG. Contemporary diagnosis and management of renal angiomyolipoma. J Urol. 2002 Oct;168(4 Pt 1):1315-25
3. Bissler JJ, Kingswood JC. Optimal treatment of tuberous sclerosis complex associated renal angiomyolipomata: a systematic review. Ther Adv Urol. 2016 Aug;8(4):279-290
4. Vaggers S, Rice P, Somani BK, Veeratterapillay R, Rai BP. Evidence-based protocol-led management of renal angiomyolipoma: A review of literature. Turk J Urol. 2021 Feb;47(Supp. 1):S9-S18
5. Vos N, Oyen R. Renal Angiomyolipoma: The Good, the Bad, and the Ugly. J Belg Soc Radiol. 2018 Apr 20;102(1):41.
6. Peng ZF et al. Efficacy and safety of sirolimus for renal angiomyolipoma in patients with tuberous sclerosis complex or sporadic lymphangioleiomyomatosis: a systematic review. J Urol. 2014 Nov;192(5):1424-30
7. Wang W et al. CT characteristics predict the response to everolimus or sirolimus of renal angiomyolipomas in patients with tuberous sclerosis complex. Int Urol Nephrol. 2019 Apr;51(4):671-676.
8. Bissler JJ et al. Everolimus long-term use in patients with tuberous sclerosis complex: Four-year update of the EXIST-2 study. PLoS One. 2017;12(8):e0180939
9. Mekahli D et al. Clinical practice recommendations for kidney involvement in tuberous sclerosis complex: a consensus statement by the ERKNet Working Group for Autosomal Dominant Structural Kidney Disorders and the ERA Genes & Kidney Working Group. Nat Rev Nephrol. 2024 Jun;20(6):402-420
10. Nozadze G, Larsen SB, Heerwagen S, Juhl Jensen R, Lönn L, Røder MA. Selective arterial embolization of renal angiomyolipomas: A 10-year experience. BJUI Compass. 2022 Jan;3(1):86-92