RENAL ANGIOMYOLIPOMA

Introduction

Angiomyolipoma (AML) of the kidney is one of the more interesting tumours found in the kidney. It is formed of heterotopic tissue and is most commonly regarded as a choristoma rather than as neoplasm. Fischer first described the tumour in 1911 and also noted and documented its association with ‘Tuberous Sclerosis’. Morgan and associates in 1951 first used the name AML.

In addition to its rarity, it has sometime evoked interest and controversy because of the difficulty in arriving at a diagnosis, differentiating it from a ‘Renal Cell Carcinoma’ and ‘Oncocytoma’ and hence deciding on a treatment option. By itself, AML is very rarely if ever known to turn malignant. Due to its relatively rare occurrence, occasional difficulty in diagnosis and controversy in management, we present this case.

Case Report

56 year old lady presented with pain and lump in the right side of her abdomen for three months. The lump increased from an initial size of 4×3 cms to the present size of 8×6 cms. Pain was dull, dragging and non-radiating. There was no associated history of hematuria, dysuria or fever with chills and rigors. There was no history suggestive of ‘Dieti's crisis’ or metastasis to lungs, liver or bone.

Clinical examination revealed an 8×6 cms irregular, firm, nontender, bimanually palpable and bellotable mass in the right flank with a colonic band of resonance anteriorly. An impression of a right sided solid renal mass, probably malignant, was made and the patient worked up. Meanwhile the patient produced a report of an FNAC having been done in a civil center and the report showed cells consistent with ‘Renal Cell Carcinoma’. Ultrasound showed a large 7.6 cms uniformly echogenic lesion ocupying almost the entire kidney sparing a bit of the upper pole. There was no obvious area of calcification, necrosis or invasion. Renal vein was patent. Overall it was suggestive of a large ‘Angiomyolipoma’ or a ‘fat containing RCC’. IVU confirmed the findings of a large right renal mass distorting and stretching the pelvi-calyceal system. CT scan showed a large lobulated mass of mixed density in the right kidney causing calyceal distortion with TU values (−81 HU). There was no evidence of any infiltration into adjacent structures, venous thrombosis, nodal enlargement or any metastasis suggesting that the mass could be benign (Fig 1). The other kidney was normal.

Fig. 1.

CT scan of the abdomen showing a large lobulated fatty mass of mixed density involving the right kidney. No evidence of infiltration, nodal enlargement, venous thrombosis or metastasis is seen.

In view of the solid nature of the tumour, one report of Renal Cell Carcinoma on FNAC and a large tumour occupying almost the entire kidney with poor renal function on that side, it was decided to perform a ‘radical nephrectomy’ on the affected side. Surgery was carried out by a right transverse transperitoneal approach. Preoperatively the tumour was involving the entire kidney. However there were no nodes or extension into the renal vein and fat planes were maintained. Post-operative recovery was uneventful.

Grossly, the specimen weighed 330 gms and measured 12×8×7 cms in dimension. The external and cut surfaces showed a fatty and pale brown tumour occupying the centre of the kidney and adjacent pale brown satellite nodules (Fig 2). Histopathology showed the typical appearance of an Angiomyolipoma with intimate admixture of mature adipose tissue, smooth muscles proliferation appearing to arise from blood vessels and thick and thin walled vessels with fractured elastic laminae (Fig 3). Areas showing foreign body granulomatous reaction to fat and melanin like pigment were also seen. No cellular atypia was seen.

Fig. 2.

Gross bisected specimen of renal angiomyolipoma showing solid and fatty areas.

Fig. 3.

Photomicrograph of angiomyolipoma showing intimate mixture of adipocytes, blood vessels and muscles seeming to arise from the vessel wall. (H&E stain × 150)

Discussion

The spectrum of renal diseases has expanded in recent years. Although most of the work taking place in this field has concerned malignant neoplasms of the kidney, there has been significant improvement in our knowledge of benign tumours and tumour like conditions. Awareness and knowledge of these benign lesions is important because they are often included in the differential diagnosis of malignant tumours with which they may be confused [1].

Renal Angiomyolipoma or hamartoma are benign tumours, which may occur as an isolated phenomenon or part of a syndrome associated with tuberous sclerosis. This is a disease that is both hereditary and familial and is characterized by mental retardation, epilepsy and adenoma sebaceum. In these patients hamartoma may also be found in the brain, eye, heart, lung and bone.

Among surgically excised renal tumours AML are relatively uncommon. Farrow and associates reported 23 cases among 2409 renal tumours found at surgical exploration of the kidney over a period of 50 years at Mayo clinic. The mean age was 41 years range 26–72 years. Male:female 2.6:1. The tumour grows slowly at the rate of 0–5 mms within 3 years.

Most AML are asymptomatic, occur in females and some present with only fever or hypertension. AML may be incidentally detected in patients undergoing CT scan for unrelated problems or in patients with tuberous sclerosis. They may present as a large abdominal lump with obstructive symptoms due to compression of duodenum and stomach. Rarely patients may present with sudden haemorrhage into the lesion causing severe pain and hypotension. Complications of this tumour are spontaneous haemorrhage especially when the tumour is larger than 4 cms in size, very rarely malignant change and IVC thrombosis [3]. Although no case of widespread metastasis has been reported, involvement of regional lymph nodes has been documented. Epitheloid AML is a recently recognized variant with malignant potential [4].

The angiographic pattern of the tumour is not sufficiently typical to reliably separate it from renal carcinoma. However the high fat content allows for a distinctive pattern on CT scan with areas having high density corresponding to fatty tissue. There are occasional reports where CT appearances were suggestive of an AML but there was evidence of calcification. These cases turned out to be Renal Cell Carcinomas. Thus the diagnosis of RCC should always be entertained in such cases [5].

Renal hamartomas are frequently bilateral. Grossly they are often yellow and grey and have a propensity for profuse haemorrhage, large size and multiplicity (Fig 2). The tumour is round to oval and elevates the renal capsule producing a bulging smooth bosselated mass. Growth is usually expansile although it can be locally invasive. Documented malignancy in AML is rare and cases reported have shown huge retroperitoneal deposists or lung nodules. Our case showed multiple satellite nodules within the affected kidney.

Microscopically, the tumour is named after the three primary components-unusual abdominal blood vessels, clusters of adipocytes and sheets of smooth muscles. Adipose tissue is of mature adult type. Smooth muscle cells are usually arranged in typical interfacing fascicles and longitudinal myofibrils are recognizable within the cytoplasm. In our case, we were able to demonstrate continuity of these fascicles with the walls of thick walled blood vessels (Fig 3).

The nuclei are frequently hyperchromatic, moderately pleomorphic and often worrisome because of the presence of frequent mitotic figures. In cases of ambiguity, reactivity for HMB-45 confirms the diagnosis [2]. This however does not reconcile with a mesenchymal origin of the epitheloid or spindle cells. Our case also showed pigment suggestive of melanin.

The natural history of renal angiomyolipoma is not well delineated. Current management options include observation, embolization, and partial or total nephrectomy. Recommendations about the treatment are usually based on the patients symptoms and size of the lesion. Dickinson M et al have classified the lesions as small (< 4 cms), medium sized (4–8cms), or large (> 8 cms). Because of the multiplicity of these tumours and their properties for bilaterality, conservative surgery is often imperative. Tumours less than 4 cms tend to be asymptomatic hence require regular follow up and no intervention. Medium sized lesions have the most variable behaviour and should be closely followed radiologically. If significant changes in symptoms or size are noted or the patient becomes symptomatic, elective intervention should be initiated promptly to increase chances of renal salvage. Large lesions or those with doubt in the diagnosis require appropriate radical surgery [6].