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1. The correct answer is: (E) autosomal recessive polycystic disease. Both kidneys are markedly enlarged, the left measuring approximately 10.8 cm, and the right 11.2 cm which is the sort of size expected in an adolescent, and approximately twice the average renal length at 6 weeks of age. In addition, both kidneys are abnormally echogenic (bright on ultrasound) with loss of normal cortico-medullary differentiation and the impression of multiple tiny cysts within the parenchyma. Microscopically, this appearance is due to fusiform dilatations of the interstitial portions of the collecting tubules. Occasionally, macroscopic renal cysts are seen in this condition although these are more often a feature of autosomal dominant polycystic kidney disease in older children and adults in whom the kidneys are not usually enlarged. In neonates, autosomal dominant polycystic disease can have similar appearances to the recessive disorder.
An ultrasound of a normal kidney at 6 weeks of age is shown for comparison in figure 5. In this case there is also fetal lobulation which is a normal variant.
Of the remaining alternative diagnoses given, bilateral Wilm's tumour (A) is a cause of renal masses rather than generalised renal enlargement unless the kidneys have been almost completely replaced by tumour, the other diagnoses (B, C, F–H) can all cause renal enlargement and may affect both kidneys, although ultrasound appearances would vary according to the specific condition.
2. The correct answer is: (C) duplication cyst. Figures 3 and 4 (from page 24) show a unilocular cyst, measuring approximately 4.5 × 3.1 × 3.2 cm, with a ‘triple-layered’ wall. Often these lesions also contain debris or fluid-fluid levels due to secreted contents. The ultrasound appearance of a triple-layered wall is pathognomonic of a duplication cyst whose wall consists of an echogenic (bright) epithelial lining representing some part of the gastrointestinal tract, a well-developed coat of smooth muscle (‘darker’ middle layer on ultrasound) and often an echogenic serosal layer externally. These are congenital lesions that may be detected antenatally and can occur anywhere along the alimentary tract. Over half are found in association with the jejunum or ileum. Fifty to sixty per cent contain gastric mucosa or pancreatic tissue and this, along with a propensity to secrete mucus makes them prone to enlargement and rupture. Other complications include ulceration or bleeding when heterotopic gastric mucosa is present in the cyst, torsion and intussusception (the lesion can act as a lead-point). The treatment is surgical resection.
Competing interests None.
Provenance and peer review Not commissioned; internally peer reviewed.