Urogenital ImagingGonadal dysgenesis
the failure of the gonads to develop in the presence of an abnormal karyotype. Gonadal failure in the presence of a normal karyotype is termed gonadal agenesis, or
pure gonadal dysgenesis. This latter category is likely a genetic disorder; it has been reported in siblings.
Gonadal failure is most often due to a chromosomal abnormality involving the X-chromosome, including aneuploidy, deletions, or fragmentations. Turner's syndrome (45,XO) is a common clinical entity associated with gonadal dysgenesis. It occurs in approximately 1 in 2,0003,000 live births. Various chromosomal mosaics also manifest gonadal dysgenesis. The most common mosaic is X/XX, with others being X/XXX, and X/XX/XXX. Gonadal dysgenesis can also be due to a genetic defect or, rarely, 17-alpha-hydroxylase deficiency.
In place of normal gonads, there is a band of fibrous tissue known as a gonadal streak. The sex hormones are not produced, and normal regulatory feedback signals to the pituitary gland and hypothalamus are absent. Gonadotrophin levels are consequently elevated. Hence, gonadal dysgenesis is also known descriptively as hypergonadotrophic hypogonadism. Primary amenorrhoea is seen in these patients. Treatment consists of sex steroid replacement. In the rare 46,XX patient with 17-alpha-hydroxylase deficiency, cortisol must also be replaced.
MRI is the best modality for imaging of these patients. MRI is superior to other imaging modalities because of its large field of view, high soft tissue resolution, and multiplanar capability. On MRI, the uterus is readily seen as being hypoplastic, and ovarian streaks are visualized as hypointense structures on T2-weighted imaging. Ultrasound is useful in the detection and initial evaluation of ovarian tumours, which are seen at a higher incidence in patients affected by gonadal dysgenesis than in the general population. See Turners syndrome
HH