Ans. a (USG cranium). (Ref. Grainger, Diagnostic Radiology, 4th ed., 2469)Cranial ultrasound of Infants# USG cranium is best method to diagnose hydrocephalus through the anterior and posterior fontanalles.# Progression of hydrocephalus can be estimated by comparison with previous studies.# USG is also helpful in following ventricular decompression in patients treated for hydrocephalus.# Neonatal hydrocephalus can also be evaluated by Doppler to assess indirectly intracranial pressure and help to determine the need for shunt placement.Cranial CT# CT enable us to evaluate the brain structure and ventricular size by noninvasive highly reliable technique.# But due to the ionizing radiations hazard, CT as a screening investigation is less preferable.Qhstretk. (Fetal) Cranial ultrasound# Obstretic ultrasound study is one of the best methods for antenatal diagnosis of hydrocephalus as it is noninvasive & hazard free not only to fetus as well as to mother. However assessment prior to GA of 20 weeks may be difficult, as ventricles constitute a large portion of cranial vault.# Signs suggestive of fetal hydrocephalus on obstretic USG study are:- Atrial size > 10 mm- Dangling "Choroid plexus" sign- BPD > 95th percentile- +- PolyhydramniosEducational points:# Lemon sign:- Concave/linear frontal contour abnormality located at coronal suture strongly associated with spina bifida.# Banana sign:- Cerebellum wrapped around posterior brainstem + obliteration of cisterna magna secondary to small posterior fossa + downward traction of spinal cord in Chiari II malformation.# Key points about Obstetric color Doppler study:- Assessment of flow in MCA is important parameter to diagnose fetal anemia.- Assessment of flow in umbilical vessels is important parameter to diagnose fetoplacental insufficiency.- Reduced diastolic flow in umbilical artery is the earliest sign of fetoplacental insufficiency.- Reversal of flow in umbilical artery (as well as pulsatile flow in umbilical vein) is the most ominous sign and may indicate impending fetal death.