Physical examination in a thin patient may detect a palpable abdominal or flank mass caused by the enlarged kidney. Causes
Hydronephrosis is the result of any of several abnormal pathophysiological occurrences. Structural abnormalities of the junctions between the kidney, ureter and bladder that lead to hydronephrosis can occur during fetal development. Some of these congenital defects have been identified as inherited conditions, however, the benefits of linking genetic testing to early diagnosis have not been determined. Other structural abnormalities could be caused by injury, surgery, or radiation therapy.The most common causes of hydronephrosis in children are anatomical abnormalities. These include vesicoureteral reflux, urethral stricture, and stenosis. The most common cause of hydronephrosis in young adults is kidney stones. In older adults, the most common cause of hydronephrosis is benign prostate hyperplasia (BPH), or intrapelvic neoplasms such as prostate cancer. Compression of one or both ureters can also be caused by other developmental defects not completely occurring during the fetal stage such as an abnormally placed vein, artery, or tumor. Bilateral compression of the ureters can occur during pregnancy due to enlargement of the uterus. Changes in hormone levels during this time may also affect the muscle contractions of the bladder, further complicating this condition.Sources of obstruction that can arise from other various causes include kidney stones, blood clots or retroperitoneal fibrosis.The obstruction may be either partial or complete, and can occur anywhere from the urethral meatus to the renal calyces.
As of 2017, chromosomal microarray analysis (CMA) was proposed to replace karyotyping because of its ability to detect smaller chromosome abnormalities and copy-number variants, leading to greater diagnostic yield in about 20% of cases. The American College of Medical Genetics and Genomics and the American Academy of Pediatrics recommend CMA as standard of care in the US. See also
Developmental disability
Epigenetics
Microcephaly
Teratology

References
Further reading
External links
Neurodevelopmental Disorders at Curlie
A Review of Neurodevelopmental Disorders - Medscape review