Elsevier

Clinical Radiology

Volume 60, Issue 6, June 2005, Pages 665-673
Clinical Radiology

Tuberose sclerosis complex: analysis of growth rates aids differentiation of renal cell carcinoma from atypical or minimal-fat-containing angiomyolipoma

https://doi.org/10.1016/j.crad.2005.01.009Get rights and content

AIM

To study the radiological characteristics of renal masses in individuals with tuberous sclerosis complex (TSC) using serial CT, and to examine how renal cell carcinoma (RCC) may be differentiated from indeterminate cysts or masses.

METHODS

This was a retrospective study of 12 cases of TSC in which dedicated renal CT followed after US had demonstrated cystic or sonographically unusual renal masses. The CT density of all masses was measured and the masses categorized as simple cysts, complex cysts, angiomyolipomas or indeterminate solid masses. Subjects were maintained on regular follow-up with repeat CT or MRI and interval renal US. Indeterminate masses that showed rapid growth were considered suspicious for renal cell carcinoma and biopsy or nephrectomy followed.

RESULTS

Comparative data were available for a median of 4 years. In each case the renal masses were multiple and bilateral; mean mass diameter was 3.6 cm. Among a total of 206 masses, 18 were simple cysts and 3 were complex cysts. Of the complex cysts, 1 proved to be an angiomyolipoma on histology and the other 2 showed no growth. Of the solid masses, 133 were typical angiomyolipomas (AMLs) and 52 were indeterminate. On follow-up, only 3 indeterminate masses showed rapid growth (>0.5 cm/year), of which only 1 proved to be an RCC on biopsy. The other 2 were minimal-fat AMLs, and the remainder of the masses showed no or slow growth.

CONCLUSION

Many renal masses associated with TSC are radiologically indeterminate. A growth threshold of >0.5 cm/year identified the only RCC in this study (0.5% of all masses). Yearly radiological follow-up of indeterminate renal masses is recommended for individuals with TSC.

Introduction

Tuberous sclerosis complex (TSC) is a multisystem genetic abnormality that presents in the kidney as simple cysts, multiple angiomyolipomas (AMLs) or, rarely, as renal cell carcinoma (RCC). Diagnostic characterization rests on imaging findings. Cysts generally do not present a problem, and on CT most AMLs contain substantial amounts of fat, easily identified with a region of interest (ROI) block. An ROI value of −10 HU or less is generally taken to indicate fat,1, 2, 3 and this is virtually diagnostic of an AML. However, some AMLs may be too small for ROI analysis4, 5 and others, so-called atypical or minimal-fat AMLs, may contain almost no fat.1, 2, 6, 7 It has been suggested that atypical AMLs may be more common in TSC8, 9 and, since the incidence of RCC in TSC is increased also,6, 9, 10 an AML with minimal or no fat may be impossible to differentiate from an RCC.

The aims of this study were to document the radiological outcome of the various types of renal masses associated with TSC in a selected cohort maintained on regular radiological follow-up. The specific question addressed was the differentiation of RCC from indeterminate renal masses and cysts.

Section snippets

Study population

A retrospective study was conducted in a teaching hospital with a tertiary referral service for clinical genetics. The study period was from March 1995 to June 2003. The study group was identified by review of the CT department database. All patients with a diagnosis of TSC, who had undergone dedicated renal CT over the study period, were eligible. Diagnosis of TSC already had been established using genetic and clinical criteria. Patients had been referred for CT because routine US had

Results

In all 12 patients, 5 men and 7 women, were included in the study. The age range was 17 to 66 years (median 24 years). All patients had from 4 to 30 multiple, bilateral renal masses; 206 masses were identified in total. The mean size of the masses was 3.6 cm (range 8 mm to 16 cm). In some kidneys additional very small lesions (<5 mm) were found, but these were too small to categorize accurately and were not further considered. Of the 206 masses, 18 were simple cysts with thin, non-enhancing walls

Discussion

TSC is an autosomal dominant disease associated with cerebral, cutaneous and visceral hamartomas. It is linked with mutations in chromosome 9 (the TSC1 gene) or 16 (the TSC2 gene). The prevalence ranges from 1:6000 to 1:10,000. The diagnosis is made by searching for the described diagnostic criteria of TSC,10, 11 supported by genetic studies in individual cases.

The commonest renal manifestation of TSC is AML, found in 80% of cases. Compared with the sporadic type, AMLs associated with TSC

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