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Original Report |
1 Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333
Burnet Ave., Cincinnati, OH 45229-3039.
2 Department of Pediatrics, Cincinnati Children's Hospital Medical Center,
Cincinnati, OH 45229-3039.
Received July 28, 2003;
accepted after revision October 8, 2003.
Address correspondence to L. F. Donnelly.
Abstract
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CONCLUSION. Multiple hepatic angiomyolipomas are often found in patients with tuberous sclerosis, particularly in those with bilateral diffuse renal angiomyolipomas.
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The association of hepatic angiomyolipomas and tuberous sclerosis has not been well described in the literature. Our purpose was to evaluate the frequency and imaging appearance of hepatic angiomyolipomas in a large series of patients with tuberous sclerosis.
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Each sonographic examination contained multiple images of the kidneys and the liver. The kidneys were the primary organs of interest, with lesions in the liver noted coincidentally. In all CT examinations, the liver and kidneys were examined in their entirety after the administration of IV contrast material (using a weight-based protocol: 2 mL/kg, up to 100 mL). Single-detector CT or MDCT was used in all cases. The report from the initial clinical interpretation was reviewed simultaneously.
Imaging studies were evaluated for the presence of hepatic angiomyolipomas. An angiomyolipoma was defined as the presence of a mass with at least a portion showing imaging characteristics consistent with fat. On sonography, fat was considered present when hyperechogenicity was equal to that of renal sinus fat. On CT, fat was considered present when attenuation was equal to that of subcutaneous and retroperitoneal fat. Eight of the 62 patients were found to have liver lesions. The mean age of these eight patients was 30 years (range, 16–40 years). The patients included five women and three men.
Imaging studies were also evaluated for the presence of renal angiomyolipomas. The number of renal angiomyolipomas was categorized as absent, fewer than five, between five and 20, and too numerous to count. Whether renal angiomyolipomas were unilateral or bilateral was also noted.
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All sonographic studies showed liver lesions that were well circumscribed, round, and hyperechoic (Fig. 1A, 1B). On CT evaluation, all liver lesions were round, well circumscribed, and showed areas of low attenuation consistent with fat (Fig. 2A, 2B). Although many lesions were homogeneous in low attenuation, some had heterogeneous areas of soft-tissue attenuation mixed with fat attenuation. The size of the lesions ranged from 0.3 to 4 cm at largest cross-sectional diameter. Of the seven patients with tuberous sclerosis who had multiple hepatic angiomyolipomas, the mean age was 30.4 years with a range of 16–40 years.
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Thirty-eight of the 62 patients in the study had bilateral diffuse renal angiomyolipomas. Liver lesions were identified only in patients with bilateral diffuse renal angiomyolipomas (Fig. 3A, 3B). Therefore, 21% (8/38) of the patients with bilateral diffuse renal angiomyolipomas also had hepatic angiomyolipomas in contrast to the 13% of patients with tuberous sclerosis in general.
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Angiomyolipomas of the liver represent a class of benign, mesenchymal neoplasms that are composed of an admixture of blood vessels, smooth muscle, and variable amounts of adipose tissue [2]. The disturbance of two genes associated with tuberous sclerosis (TSC1, band 9q34 and TSC2, band 16q13.3) that may act as tumor suppressor genes could account for the existence and growth of angiomyolipomas in tuberous sclerosis [2]. The most frequent abdominal manifestation of tuberous sclerosis is multiple renal angiomyolipomas, occurring in up to 80% of patients. A series of studies has shown that these lesions increase in size, distort the renal architecture, and often lead to renal failure. Spontaneous hemorrhage is also a risk for those patients with angiomyolipomas, with larger angiomyolipomas being more susceptible to hemorrhage than smaller angiomyolipomas.
Monitoring tuberous sclerosis patients with renal angiomyolipomas for the purposes of prognostic information and potential prophylactic therapeutic intervention has become routine [2]. As a result of this monitoring, hepatic lesions in patients with tuberous sclerosis have been recognized with increasing frequency. The literature describes the imaging appearance of lipomatous hepatic lesions, similar in imaging appearance to renal angiomyolipomas, in patients with tuberous sclerosis [1, 3–12]. The sonographic appearance of these lesions has been described as smoothly contoured homogeneous hyperechoic masses with a well-defined border separating the mass from normal hepatic tissue [1, 3–8, 11]. Unenhanced CT shows these lesions as well-defined hypoattenuating lesions [5, 6, 8, 10]. Although several reports of homogenous lesions on contrast-enhanced CT have been made, the attenuation is typically heterogeneous because of the variable composition of the lesions [5, 6, 9, 10, 12]. The lesions in our series showed an imaging appearance similar to that described in the literature. In our series of tuberous sclerosis patients, 13% were found to have liver lesions with the imaging appearance of angiomyolipomas. Of those patients with liver lesions, the lesions in seven (88%) of eight had multiple lesions. All patients with hepatic lesions had bilateral diffuse renal angiomyolipomas.
The literature has also suggested a higher frequency of multiple hepatic angiomyolipomas in females with tuberous sclerosis [1, 3–12]. In the literature, of the 40 patients with both multiple hepatic lesions and tuberous sclerosis, 33 (83%) were female [1, 3–12]. In our study, five (71%) of seven patients with tuberous sclerosis and multiple hepatic lesions were female.
The finding of multiple hepatic lesions in a patient with tuberous sclerosis is not a cause for concern. From data collected in our study and reported in the literature, multiple hepatic angiomyolipomas are a stigma of tuberous sclerosis and should be an expected finding in a certain percentage of patients [1, 3–12]. When the characteristic imaging findings are present, further diagnostic workup, such as biopsy, is not indicated. The significance of these lesions is indeterminate at present. One study in the literature reported a hepatic angiomyolipoma in a patient with tuberous sclerosis that spontaneously ruptured with subsequent hemorrhage [12]. The article suggested that hepatic lesions greater than 4 cm in diameter should be monitored every 3 months for increased growth, which is also the recommendation for monitoring renal angiomyolipomas [2, 12].
Because of the lack of large long-term follow-up studies, no recommendations have been made concerning hepatic angiomyolipomas 4 cm or smaller in diameter. We found hepatic lesions only in patients with bilateral diffuse renal angiomyolipomas. However, hepatic lesions may not have been identified in patients evaluated on sonography alone. Despite this qualification, if a hepatic lesion is identified in a patient with tuberous sclerosis and without renal angiomyolipomas, other abnormalities should be suspected such as an adenoma, a hemangioma, or a carcinoma.
This study has limitations, including the small number of patients and radiologic examinations. Still, it is a large compilation of patient data concerning hepatic lesions in tuberous sclerosis patients. This study is also limited by its retrospective nature. The imaging studies were not performed at set ages and were not done for scientific investigation, but rather for clinical indication. Despite its limitations, our study provides valuable information concerning the incidence of hepatic lesions in tuberous sclerosis and the imaging characteristics of hepatic lesions in tuberous sclerosis and strengthens the idea of a link between multiple hepatic angiomyolipomas and tuberous sclerosis. This information adds strength to two prior reports concerning the association of multiple hepatic angiomyolipomas and tuberous sclerosis [3, 4]. A prospective collection of data, as mentioned previously, may provide additional and more complete information.
In conclusion, multiple hepatic angiomyolipomas are often found in patients with tuberous sclerosis and particularly in patients with bilateral diffuse renal angiomyolipomas. Multiple hepatic angiomyolipomas are stigmata of tuberous sclerosis, and their finding should not be surprising or provoke unnecessary biopsy in a patient with known tuberous sclerosis. The finding of multiple hepatic angiomyolipomas in a patient not diagnosed with tuberous sclerosis is reason to evaluate this patient for further evidence of tuberous sclerosis.
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