Urogenital Imaging

Haemoglobinopathy, renal manifestation

Abnormality of the haemoglobin gene is seen in patients with sickle cell anaemia. Individuals with homozygous haemoglobin S gene (haemoglobinopathy-S) are afflicted with sickle cell anaemia. It occurs in approximately 10% of African Americans and 30% of black Africans. Patients who are heterozygous for the haemoglobin S gene have sickle cell trait and milder symptoms. A point mutation in the haemoglobin gene results in substitution of valine for glutamic acid, which results in an abnormal gene product. The affected erythrocytes assume a "sickle" shape when exposed to hypoxic conditions, and they are less malleable than normal erythryocytes. These cells tend to aggregate and occlude capillaries, resulting in ischaemia and infarction in the renal medullae and papillae. For description of imaging findings, see ischaemia renal

Papillary necrosis is seen in up to 50% of patients with sickle cell disease. It is also seen, though to a lesser degree, in patients with sickle cell trait. Medullary ischaemia results in necrosis and sloughing of papillary tissue. In turn, papillary necrosis can induce interstitial nephritis. Affected patients may present with acute symptoms such as haematuria and colic due to massive sloughing of papillary tissue. Alternatively, papillary necrosis can be an indolent process with subclinical symptoms. In conjunction with clinical findings, the diagnosis can be made by excretory urography. Papillary fragments may also be found in the urine.

In patients with homozygous-S disease, bilaterally enlarged kidneys with smooth contours are seen. Renal enlargement is presumably due to vascular dilatation, glomerular enlargement, interstitial oedema and increased renal blood flow. Additional radiological findings include impaired density of contrast agent and dilatation of the collecting system due to defective water concentrating ability. The above findings are best appreciated on excretory urography and CT. Sonography shows nonspecific renal enlargement. Decreased signal intensity on T2-weighted MR images has been reported. See ischaemia renal and Papillary necrosis

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