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