Derived from the genital tubercle the labia majora and scrotum
354 Answers to Problems
|
|---|
4. The uterus is formed by fusion of the lower por-tions of the paramesonephric ( müllerian) ducts. Numerous abnormalities have been described; the most common consists of two uterine horns (bicornuate uterus). Complications of this defect include diffi culties in becoming pregnant, high incidence of spontaneous abor-tion, and abnormal fetal presentations. In some cases, a part of the uterus has a blind end (rudi-mentary horn), causing problems with men-struation and abdominal pain.
4. The child most likely has a thyroglossal cyst that results from incomplete regression of the thyroglossal duct. These cysts may form any-where along the line of descent of the thyroid gland as it migrates from the region of the foramen cecum of the tongue to its position in the neck. A cyst must be differentiated from ectopic glandular tissue, which may also remain along this pathway.
|
|---|
4. The embryological basis for most neural tube defects is inhibition of closure of the neural folds at the cranial and caudal neu-ropores. In turn, defects occur in surround-ing structures, resulting in anencephaly, some types of encephaloceles, and spina bifi da cys-tica. Severe neurological defi cits accompany abnormalities in these regions. Neural tube defects, which occur in approximately 1 in 1,500 births, may be diagnosed prenatally by ultrasound and fi ndings of elevated levels of a-fetoprotein in maternal serum and amni-otic fl uid. Recent evidence has shown that daily supplements of 400 mg of folic acid started 3 months prior to conception prevent up to 70% of these defects.
5. This condition, hydrocephalus, results from a blockage in the fl ow of cerebrospinal fl uid from the lateral ventricles through the foram-ina of Monro and the cerebral aqueduct into the fourth ventricle and out into the sub-arachnoid space, where it would be resorbed. In most cases, blockage occurs in the cerebral aqueduct in the midbrain. It may result from genetic causes (X-linked recessive) or viral infection (toxoplasmosis, cytomegalovirus).
