An unusual renal mass

A woman aged 52, otherwise fit and well, was admitted as an emergency with the history of a sudden onset constant back pain on the right hand side, for the past four hours.

On examination her vital signs were blood pressure: 130/78 mm Hg; pulse 80/minute.

Fig 1 Ultrasound scan of abdomen

Abdominal examination was unremarkable, except for mild tenderness in the right renal angle. All blood investigations including inflammatory markers and liver function tests were within normal limits, with a haemoglobin of 12¥10 g/l. The haemoglobin suddenly dropped to 8¥10 g/l a day after admission. The patient was stabilised with fluid resuscitation and blood transfusion. She had an ultrasound scan of the abdomen (fig 1) and subsequently a computed tomography scan (fig 2).

Fig 2 Computed tomography scan of abdomen
 

Questions

1. What do the ultrasound and computed tomography scans show?
2. What is the incidence, mean age, and sexual distribution of this condition, and does it affect one side more than the other?
3. Name two conditions associated with it.
4. What procedure does the images below show?

Answers

1. The ultrasound shows a highly echogenic tumour in the right kidney, due to high fat content, and the computed tomography scan shows a heterogeneous tumour predominantly of fat density, both suggesting the possibility of angiomyolipoma of the right kidney.
2. The incidence is 0.3-3%,¹ the mean age of presentation is 43 years, and the tumour is more common in women; 80% of the cases affect the right kidney.
3. Tuberous sclerosis is commonly associated with it and rarely lymphangioleiomyomatosis.²
   
4. Figures 3 and 4 show the procedure of renal artery embolisation used to shrink tumours. Renal arterial embolisation is a technique that blocks the renal artery that feeds the kidney with the tumour. Renal artery embolisation is used primarily as a preoperative measure to minimise intraoperative blood loss and as a primary therapy in some vascular tumours like angiomyolipoma. This is done by injecting small solid particles (such as metallic coils or gel foam) or special liquid agents (such as absolute alcohol or isobutyl-2-cyanoacrylate) through a small catheter passed through the femoral artery in the groin.
   

   
Fig 3 and fig 4 Right kidney

Discussion

Angiomyolipoma (AML) is a benign renal neoplasm composed of fat, vascular, and smooth muscle elements.³ There are two types, isolated angiomyolipomas and angiomyo­lipomas associated with tuberous sclerosis.¹

Isolated angiomyolipoma, which occurs sporadically, often is solitary and accounts for 80% of the tumours. The mean age of patients at presentation is 43 years, and isolated angiomyolipomasis is more common in women than in men.¹ Interestingly, 80% of the cases affect the right kidney.

Angiomyolipoma associated with tuberous sclerosis accounts for 20% of the tumours; these lesions are typically larger than isolated angiomyolipomas, and they are often bilateral and multiple.¹

Tuberous sclerosis and angiomyolipoma

Tuberous sclerosis complex (TSC) is a multiorgan disorder with an estimated prevalence of 1 in 10 000. It has autosomal dominant transmission, and 30% of patients have relatives with tuberous sclerosis complex.³ The principal lesion is the hamartoma, which occurs in the brain (cortical tubers), retina (phakomas or hamartomas), skin (angiofibromas or adenoma sebaceum), heart (rhabdomyomas), bone (sclerotic lesions), lung (lymphangiomyomas), and kidney (angiomyolipoma and renal cysts).³

Diagnosis is based on clinical, radiological, and histopathological findings, with facial angiofibroma, multiple ungual fibromas, and multiple subependymal calcifications being pathognomonic of tuberous sclerosis complex.³ Renal angiomyolipomas are composed of varying amounts of mature adipose tissue, smooth muscle, and thick walled blood vessels.

In adults with tuberous sclerosis complex, results from several studies of postmortem examination imply a prevalence of renal angiomyolipoma of 40-80%, and one study showed a prevalence of angiomyolipoma of 75% in 60 children younger than 19 who had tuberous sclerosis complex.⁴Patients with tuberous sclerosis complex commonly have bilateral and multiple renal angiomyolipoma, and tumours often extend into the perinephric space.³

Clinical presentation

Most angiomyolipomas are asymptomatic. Symptomatic patients usually present late in the third to fourth decades of life with flank pain, lump, haematuria, and occasionally shock due to spontaneous retroperitoneal haemorrhage from pseudoaneurysms.¹ These complications occur mainly in tumours that are over 4 cm in diameter.

Differential diagnosis include renal infarction, liposarcoma, lipoma, renal cell carcinoma, atypical Wilm's tumour containing excess adipose tissue (not normally present in typical Wilm's tumour), lipomatosis, and oncocytoma.¹⁵

Investigations

Firstly, ultrasonography: shows that angiomyolipomas are intensely echogenic renal tumours and can cause acoustic shadowing (which is a sonographic appearance) because of their high fat content.¹⁶

Secondly, computed tomography scan: usually shows that angiomyolipoma is a well marginated cortical hetero­­,geneous tumour with predominately fatty attenuation.¹⁶

Thirdly, magnetic resonance imaging: the characteristic appearances of angiomyolipomas include variable areas of high signal intensity within the tumour.¹⁶

Fourthly, percutaneous fine-needle biopsy or aspiration cytology: a diagnosis of angiomyolipoma is suggested if smooth muscle cells and mature fat cells can be identified in the aspirated renal material.⁶ Fine-needle biopsy generally is not considered to be a reliable technique in the characterisation of renal masses and carries a serious risk of haemorrhage.

Ultrasonography and computed tomography scanning are usually very effective in the diagnosis of angiomyo­lipoma. Magnetic resonance imaging and needle aspirations can be used when diagnostic dilemma still exists.

Treatment

The treatment for angiomyolipoma depends on the size of the tumour and symptoms.

• If the lesion is smaller than 4 cm, ultrasound observation every six months is appropriate.⁷
  
• If the lesion equals 4 cm or larger and the patient is asymptomatic, observation may be appropriate, although some favour active treatment.⁷⁸
  
• If the lesion is bigger than 4 cm and the patient is ­symptomatic a) Angiographic embolisation, or b) Partial nephrectomy or nephron sparing nephrectomy, if ­possible.^{7 8}
  
• In certain cases, radical nephrectomy may be needed, when kindey sparing surgery is not possible, owing to the exte­nsive nature of the disease or when the diagnosis is equivocal.⁸
  

In our particular case, the patient underwent right radical nephrectomy after embolisation, because of the extensive nature of the disease. She is currently being followed up by ultrasound every six months for her other kidney.

Competing interests: None declared.

Impress your mates at the pub with your startling repertoire of esoteric medical knowledge

Balakrishnan Saravanan, senior house officer, Department of Urology, Ysbyty Gwynedd
Email: b_sarabala75@rediffmail.com
Siddharth Neminathan, senior house officer, Department of Urology, Ysbyty Gwynedd
Kevin J Thomas, consultant urologist, Department of Urology, Ysbyty Gwynedd



studentBMJ 2006;14:265-308 July ISSN 0966-6494

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