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Keywords:

  • Renal angiomyolipoma;
  • management;
  • tuberous sclerosis

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Objective

To evaluate the clinical, therapeutic and prognostic aspects of renal angiomyolipoma (AML) in patients either monitored by clinical and radiological follow-up or treated by surgical therapy.

Patients and methods

Fifty-three patients with renal AML were divided in two groups; 33 patients in group 1 were monitored by annual clinical and ultrasonographic follow-up and 20 in group 2 were treated with surgical therapy. Two patients had tuberous sclerosis (TS) with synchronous bilateral and multiple lesions. Apart from the patients with TS, there were 38 lesions in group 1 and 25 in group 2. The mean (range) follow-up of group 1 was 60.2 (12–164) months.

Results

In group 1, the diagnosis was most often incidental, after ultrasonography performed for symptoms unrelated to AML. In group 2, the suspicion of a malignant renal lesion, and spontaneous tumour rupture with bleeding and perirenal haematoma, were the main indications for surgical treatment. The mean lesion diameter was significantly greater in group 2 (5.4 cm) and in symptomatic patients (8.1 cm). In group 1, 92% of renal AMLs showed no radiographic changes, serious complications or new renal or extrarenal lesions during the follow-up. Only three lesions grew, after 22, 85 and 164 months, respectively. Of the 20 patients in group 2, 14 underwent conservative surgery.

Conclusion

Small (<4 cm) isolated AMLs, detected incidentally, showed a low risk of developing during long-term follow-up. Such patients may be followed conservatively by ultrasonography every 2 years. Spontaneous perinephric haemorrhage is related to the size of the lesion. When surgery is indicated (by symptoms or diagnostic doubt), a conservative procedure can be performed in most of cases.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Angiomyolipoma (AML) is an uncommon benign tumour (hamartoma) composed of mature or immature fat, thick-walled blood vessels and smooth muscle elements in varying proportions. There are two varieties of renal AML, one associated with tuberous sclerosis (TS or Bourneville disease) or other facomatosis (von Recklinghausen's neurofibromatosis and von Hippel Lindau's disease) and another that appears as an isolated lesion [1[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]–18]. In the first case, renal AMLs are most often multiple, bilateral, symptomatic and without female or male predominance. Renal AMLs were found in 40–80% of patients with TS [1]. In the second case, renal AMLs are single, often asymptomatic, have a female predominance and are typical of the fifth and sixth decades of life.

The widespread use of abdominal ultrasonography (US) has increased the incidental detection of isolated renal AMLs. This condition, associated with the uncertain natural history of AMLs, makes the therapeutic strategy problematic, i.e. a choice of clinical and radiological follow-up, superselective arterial embolization, radical or conservative surgery.

The purpose of this study was to review patients with renal AMLs treated at our institution in the last few years to evaluate the clinical, therapeutic and prognostic aspects; patients were either monitored or treated with surgical therapy.

Patients and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Between 1982 and 1997, 53 patients with renal AML were referred to our institution. Group 1 comprised 33 patients who were followed with an annual physical examination and renal US, and group 2 comprised 20 patients who underwent surgery; their details are given in Table 1. TS was present only in two patients (one man and one women, 28 and 41 years old, respectively); both had bilateral and multiple lesions, ranging from 1 to 6 cm. Apart from the patients with TS, there were 38 lesions in group 1 and 25 in group 2. The man with TS was included in both groups because he had previously undergone surgery for two renal AMLs and then was monitored for the remaining lesions. The results were evaluated statistically using the Mann–Whitney U nonparametric test.

Table 1.  Characteristics of the 53 patients in the present study Thumbnail image of

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

In both groups, renal AMLs were generally unilateral, with 25 (76%) in group 1 and 14 (70%) in group 2, and solitary; the laterality and sizes are detailed in Table 1. Three of six patients in group 2 with bilateral AMLs (including patients with TS) underwent bilateral surgery in two steps.

In group 1, the diagnosis was most often incidental, after ultrasonography for symptoms unrelated to AML (Table 2). Only two patients, with 5- and 6-cm AMLs, had a mild and desultory flank pain; the pain was ipsilateral to the lesion and bilateral, respectively. In group 2, the suspicion of a malignant renal lesion (half the patients), spontaneous tumour rupture with massive bleeding and perirenal haematoma (35%), and haematuria (15%) were the main indications for surgical treatment. Half the AMLs operated to clarify the histological features of the lesions were <4 cm. The mean (range) lesion diameter was 8.1 (2.5–17) cm (80%>4 cm) in symptomatic and 2.0 (0.3–10) cm (92%<4 cm) in asymptomatic patients (P<0.0001). In group 1, the mean (range) lesion diameter was 1.5 (0.3–6) cm (95%<4 cm) while in group 2 it was significantly greater, at 5.4 (1–17) cm (60%≥4 cm; P<0.0001).

Table 2.  Causes of diagnosis in group 1 Thumbnail image of

In group 1, 35 renal AMLs (92%) showed no radiographic changes, serious complications or new renal or extrarenal lesions during the follow-up. The remaining three lesions increased (mean 0.8 cm, range 0.6–1) during the follow-up of 22, 85 and 164 months, respectively; the initial lesion diameters were 1.2, 0.9 and 1.5 cm, respectively. The AMLs in the man with TS (who had previously undergone partial nephrectomy for two AMLs of 2 and 6 cm, which increased to 2.4 and 1.4 cm, respectively, in 31 months) did not change during a follow-up of 81 months.

Fourteen of the 20 patients in group 2 underwent conservative surgery (17 enucleations, one partial nephrectomy), including a patient with a 17-cm AML. A patient who had undergone superselective renal embolization 3 months previously required enucleation because of massive intrarenal bleeding. Nephrectomy was performed in four patients; in three to clarify the histological features of the lesions and in one for spontaneous rupture of the tumour. This latter case was a woman with TS who required nephrectomy on the left side because of spontaneous rupture of two AMLs of 3 and 6 cm. One year later she required a nephrectomy on the right side because of intrarenal massive bleeding of multiple AMLs (haemoglobin 75 g/L).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Renal AML is a benign tumour (hamartoma), composed of fat, smooth muscle and vascular components. Multiple renal AMLs are common in patients with TS but rare in patients without [1,3[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]–19]. Multiple AMLs have been reported in lymph nodes, spleen, liver, inferior vena cava and retroperitoneum [20[21][22][23][24]–25]. The clinical use of US of the abdomen has increased the incidental detection of renal AMLs. Renal AML has a female predominance; the male to female ratio is 1:3 or 1:4 [1,6,8,9,11]. In the present patients, only group 2 had such a ratio (1:4), while in group 1 neither sex was predominant. This may be explained because there are generally more male patients in urological departments than in, e.g. radiological departments.

The size of the lesion was the criterion used by Steiner et al. [1] to evaluate the growth of renal AMLs and by Oesterling et al. [6] to determine the management of AMLs. Steiner et al. [1] reported 24 patients with 28 AMLs, followed by observation with serial CT for a mean of 4.0 years. The authors found that four of 15 AMLs of <4 cm diameter and six of 13 AMLs of >4 cm diameter grew. Oesterling et al. [6] reported 13 patients with 17 renal AMLs, followed with CT for a mean of 4.8 years; five AMLs of 17 were <4 cm and 12 were ≥4 cm. All patients with lesions of <4 cm were asymptomatic, while six with AMLs of ≥4 cm were symptomatic. None of the 17 lesions (range 1–19 cm) showed any radiographic changes or had any serious complications. In that study, the authors reviewed the literature and proposed a therapeutic strategy on the basis of lesion diameter and symptoms. In the present experience, isolated AMLs, incidentally detected, were often small (95%<4 cm), and grew infrequently and slowly. In group 1, only three of the 38 lesions showed a slow increase in a minimum follow-up of 22 months. These cases only require physical examination and renal US every 2 years.

Diagnostic doubt was the main indication for surgery (half the lesions<4 cm), while a third of patients in group 2 were operated for symptomatic lesions (80%>4 cm). The typical findings on ultrasonography, a round and well-defined hyperechoic mass (grade 3 or 4 echogenicity) [3,8[9][10][11][12][13][14][15][16]–17], is not always present. In the present study, there was a wider range of echogenicities, including hypoechoic AML lesions. Paivansalo et al. [20] examined hypoechoic AMLs and showed the presence of more myogenic components than their more echogenic counterparts. Moreover, it is not easy to diagnose AMLs with a low mature fat content, bleeding and necrosis [4,11,20,27]. In cases of diagnostic doubt, we suggest surgical exploration and we never perform percutaneous biopsy.

The main complication of AML is spontaneous perinephric haemorrhage, which is considered to be related to the size of the lesion [1,2,6,11]. In patients with tumour rupture and massive bleeding (seven of 20 in the present study) the lesion was significantly larger than in asymptomatic patients (8.4 cm vs 2.0 cm, respectively; P<0.0001). Once surgical treatment is selected, it should be conservative because of the benign biological features of renal AMLs; patients may also have AMLs in the contralateral kidney. In the present study, conservative surgery was performed in 14 of 20 patients; a large lesion is not a contraindication to conservative surgery, as one of the present patients underwent enucleation of a 17-cm AML.

The close relationship between AMLs and TS may increase the risk of misdiagnosis and spontaneous tumour rupture. In the study of Steiner et al. [1] patients with TS were more frequently symptomatic and required surgery; this condition was confirmed by our experience.

The development of renal AML to a neoplasm and the incidence of renal AML involving other organs is unknown; only one case has been reported which led to death by perforation of the colon and invasion of the diaphragm [28]. In the present study, none of the AMLs showed neoplastic change or association with RCC.

We conclude that small, isolated AMLs, detected incidentally, may be followed conservatively by US every 2 years. Diagnostic doubt is the main indication for surgery. Spontaneous perinephric haemorrhage is related to the size of the lesion. Patients with AMLs of >4 cm should be warned of the risk of spontaneous tumour rupture with massive bleeding. Conservative renal surgery is possible for most AMLs.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References