Giant bilateral angiomyolipoma of the kidney

Abstract

Angiomyolipoma is a benign solid renal neoplasm. A giant angiomyolipoma is more than 10cm by size, but it can grow to huge proportions. Our case appears to be the third largest angiomyolipoma and the largest among bilateral giant renal angiomyolipoma in the indexed literature. A 26-year-old man presented with large right abdominal swelling for the past three years, which was occupying his right flank and iliac region, extending beyond the midline. Computed tomography of the abdomen revealed a large well-defined mass in the right side of the abdomen, crossing the midline and measuring 35 × 20 × 12cm. The left kidney showed a similar fatty lesion of 14 × 6cm. The findings were consistent with angiomyolipoma. Further evaluation for tuberous sclerosis by magnetic resonance imaging the brain demonstrated multiple subependymal nodules. Giant renal angiomyolipoma is an uncommon tumour with bilateral giant angiomyolipoma being a rare entity. Preoperative embolisation helps in reducing size of the tumour. In case of giant and bilateral angiomyolipoma, evaluation for tuberous sclerosis should always be done.

Background

Angiomyolipoma is a benign hamartomatous solid tumour of the kidney consisting of mature adipose tissue, smooth muscle and thick-walled vessels,¹ with a prevalence of 0.2–0.6% and a strong female predilection.² It accounts for 3% of the solid renal masses.³ The term ‘giant angiomyolipoma’ is defined as a tumour greater than 10cm.⁴ We report a case of bilateral giant renal angiomyolipoma which occupied the patient’s right side completely and more than half of the abdomen. It appears to be the third largest angiomyolipoma and largest among bilateral giant renal angiomyolipoma in the indexed literature.

Case history

A 26-year-old male presented with a large right-sided abdominal swelling for the past three years, which was slowly increasing in size and was associated with vague abdominal pain. He had no urinary or gastrointestinal symptoms. On inspection, the abdomen was distended; the swelling was seen in the right flank and iliac region, extending beyond the midline. On palpation, it was non-tender, firm in consistency and had a smooth surface. It extended from the right subcostal to the iliac region and also beyond the midline.

His haemoglobin was 9.8 g/dl, but other laboratory investigations (including kidney function tests) were essentially normal. On ultrasound, a large right-sided retroperitoneal tumour measuring 33 × 18 × 12cm replacing the right kidney was seen, and a similar lesion was present in the left kidney measuring 12 × 6cm. Both lesions were suggestive of angiomyolipoma. Computed tomography (CT) of the abdomen revealed a large well-defined mass in the right side of the abdomen, crossing the midline and extending from D11 to the coccyx, predominantly in the retroperitoneum (Figure 1). The mass was heterogeneous, replacing and distorting the right renal parenchyma and collecting system with areas of soft tissue and fat components (Hounsfield units of −80), measuring 35 × 20 × 12cm. Intermixed within this fatty mass were areas of tissue density corresponding with smooth muscles and blood vessels. The mass was encasing the right renal vessels.

Figure 1 .

Computed tomography (coronal section) showing giant right angiomyolipoma occupying more than 50% of the abdomen and going into the pelvis

The left kidney showed a similar fatty lesion of size 14 × 6cm. Findings were consistent with angiomyolipoma (Figures 2, 3). The patient was re-evaluated for the possibility of tuberous sclerosis. There was no history of mental restriction, epilepsy or adenoma sebaceum and no dermatological lesions. However, a magnetic resonance image (MRI) of the patient’s brain demonstrated multiple small subependymal nodules, which indicated tuberous sclerosis (Figure 4). Immunotesting for HMB45 was not available in our hospital. The patient was prepared for preoperative embolisation followed by surgery. However, because of an emergency in the family, the patient left hospital before surgery. He was contacted by telephone for about 10 months, but he refused any treatment and is lost to follow-up.

Figure 2 .

Computed tomography: axial section (left) showing bilateral renal angiomyolipoma; coronal section (right)

Figure 3 .

Computed tomography (axial section) showing right side totally occupied by the tumour and bowel loops pushed towards the left side

Figure 4 .

(Left) Magnetic resonance image of the brain (axial section) showing subependymal nodules in lateral ventricles. (Right) Susceptibility weighted image showing calcified subependymal nodules

Discussion

Renal angiomyolipoma is a benign neoplasm arising from mesenchymal tissues.⁵ It is typically a solid triphasic tumour composed of varying amounts of three elements: dysmorphic blood vessels, smooth muscle components and mature adipose tissue.⁶ It usually presents in middle-aged women and accounts for 3% of the solid renal masses.³ Some 80% of renal angiomyolipomas are sporadic and remaining 20% are associated with tuberous sclerosis complex.⁷ Tuberous sclerosis is an autosomal dominant disease with incomplete penetrance. Its prevalence in the literature varies from 1/6,000 to 1/12,000 individuals.⁸ Of those patients with tuberous sclerosis, 55–75% may have renal angiomyolipoma.^9,10 Other renal manifestations of tuberous sclerosis complex are renal cysts and, rarely, renal cell carcinomas. In contrast to the sporadic form of angiomyolipoma, hereditary lesions of angiomyolipoma affect both men and women equally and manifest in the second or third decade.¹¹ They are usually large, multiple and bilateral, and are prone to grow more aggressively,¹² up to 30cm in diameter.^13,14

Renal angiomyolipoma is largely an incidental radiological finding; most patients are asymptomatic when they receive the diagnosis.² Symptomatic presentation is most frequently related to spontaneous retroperitoneal haemorrhage due to a haemorrhagic aneurysm, although this is seen in less than 15% of cases.² It leads to one-third of the patients presenting with shock, and thus the risk of haemorrhagic shock is the main clinical concern in a patient with angiomyolipoma. Other symptoms include a palpable mass, flank pain, haematuria, anaemia, urinary tract infection or renal failure.¹⁵

About 50 cases of giant renal angiomyolipoma have been reported to date in the indexed literature, Most of which were unilateral. The literature was searched using PubMed and the Cochrane Library for the keywords ‘giant angiomyolipoma’ and ‘bilateral angiomyolipoma’ for the period 1979–2019. The search on PubMed yielded 23 results, while MEDLINE and the Cochrane Library did not produce any results. Our case appears to be the third largest angiomyolipoma and the largest among bilateral giant renal angiomyolipomas in the indexed literature (Table 1).

Table 1 .

Giant renal angiomyolipoma in the indexed literature, by size

Study	Year	Size (cm)	Side	Tuberous sclerosis	Bilateral
Katz et al29	1997	45 × 20 × 12	Left	Yes	No
Taneja et al30	2013	39 × 25 × 9	Left	No	No
Current case	2020	35 × 20 × 12 (R) and 14 × 6 (L)	Both	Yes	Yes
Hussain et al31	2013	32 × 16 × 12 (R) and 27 × 21 × 16 (L)	Both	Yes	Yes
Barbará et al32	2004	31 × 19 × 10 (L) and 14 × 5.5 (R)	Both	Yes	Yes
Castillo et al13	1987	30 × 25 × 20	Left	No	No
Alshehri et al14	2020	30 × 22 × 20	Right	No	No
Tong et al33	1980	30		No	No
Zhou et al34	2015	28 × 20 × 14 (R) and 12 × 9 × 6 (L)	Both	No	Yes
Eason et al35	1979	28 × 16 × 9	Left	No	No
Hsu et al36	2002	24 × 17 × 10	Right	No	No
Cichocki et al37	2014	22.5 × 9.5 × 10.4	Left	No	No

Imaging plays a major role in the diagnosis and management of renal angiomyolipomas. The detection of adipose tissue is the fundamental diagnostic criterion of a classic angiomyolipoma.² On ultrasound, a classic angiomyolipoma is markedly hyperechoic to renal parenchyma, owing to the presence of fat.¹⁶ The image-based detection of fat is aided by CT,¹⁷ which correctly diagnosed angiomyolipoma in 75–86% of cases.¹⁸ The presence of fat, which is highly suggested by attenuation less than −10 HU, is diagnostic of renal angiomyolipoma.^19,20 MRI can determine the amount of intravoxel fat, which helps in the diagnosis of angiomyolipoma.²¹ The ‘Indian ink artefact’, which refers to the loss of signal at the border of the mass and renal parenchyma, is indicative of an angiomyolipoma.²²

Although the diagnosis of angiomyolipoma can usually be established by imaging alone, percutaneous biopsy is sometimes advocated when uncertainty persists after radiographic imaging. Needle biopsy is not widely used for diagnosing renal masses because biopsy results often do not affect the subsequent management of renal masses, including angiomyolipoma, since negative biopsy does not exclude possible malignancy in giant angiomyolipomas.³ Positive immunoreactivity for HMB45, a monoclonal antibody raised against a melanoma-associated antigen, is characteristic for angiomyolipoma and can be used to differentiate this tumour from sarcoma and other tumours.²³

Giant renal angiomyolipomas are usually slow growing tumours, usually at the rate of 5% per year or 0.19cm/year.²⁴ They can rarely reach a large size but, in our patient, it was of enormous proportions, occupying the right side completely, together with more than half of the abdomen, pushing the bowel loops to the left side.

The management of angiomyolipomas has been correlative with symptoms. Primary indications for intervention are symptoms such as pain or haemorrhage, or the suspicion of malignancy.³ The risk of haemorrhage and the frequency of symptoms increases with the size of the angiomyolipoma.²⁵ Thus, selective arterial embolisation is the first line of treatment for patients with larger-sized tumours.²⁶ In selected high-risk patients, such as patients with whom regular follow-up is difficult, prophylactic embolisation (asymptomatic tumour of 4cm or larger) is recommended.¹⁶ The size of the tumour usually decreases by two-thirds.⁴ The principle indications of surgical intervention are persistent haemorrhage, suspicion of malignancy or failed embolisation.⁴ The benign nature of renal angiomyolipoma favours nephron-sparing surgery.³ In cases of bilateral lesions, as seen in tuberous sclerosis, nephron-sparing surgery should be performed.²⁷ Total nephrectomy should be reserved for patients with life-threatening haemorrhage and near total replacement of renal tissue.²⁸

Conclusion

Giant renal angiomyolipoma is an uncommon tumour, with bilateral giant angiomyolipoma being a rare entity. It is rare for angiomyolipoma to occupy the right side completely and more than half of the abdomen. CT is diagnostic tool identification of classic angiomyolipoma. Preoperative embolisation helps in reducing size of the tumour. In cases of giant and bilateral angiomyolipoma, evaluation for tuberous sclerosis should always be done.