holoprosencephaly is a complex brain malformation resulting from incomplete cleavage of the prosencephalon , occurring between the 18 and the 28 day of gestation , with an estimated incidence of 1/16,000 live births and 1/250 conceptuses . three ranges of increasing severity are described : lobar , semi - lobar , and alobar holoprosencephaly . although hydrocephalus can occur during pre- or postnatal development we report here a case of hydrocephalic holoprosencephaly who developed csf ascites following a ventriculoperitoneal shunt ( vp shunt ) and discuss the possible factors involved in this development . a five month - old male child presented with complaints of enlarging head size and poor feeding . a diagnosis of holoprosencephaly was established on performing a ct scan of the head [ figure 1 ] . following this , the patient became symptomatically better after the shunt and a repeat ct scan of the head showed the shunt tip in situ [ figure 2 ] . one month after the shunt , the child presented with progressive distension of the abdomen and decreased feeding . on examination , he was found to have a grossly distended abdomen , fluid thrill and sluggish bowel sounds . the head circumference was 47 cm . a ct scan of the head revealed enlarged the shunt to still be in situ . ct of the abdomen also showed gross ascites without any evidence of loculated fluid collection or lymphadenopathy [ figure 3 ] . under ultrasound guidance , the shunt was exteriorized from the abdominal end , following which abdominal distension decreased and there was improvement in feeding . a new vp shunt was done with the shunt valve upgraded to a medium pressure valve . following this procedure , plain ct scan of the head showing agenesis of bilateral cortical structures seen in alobar holoprosencephaly , along with associated hydrocephalus plain ct scan of the head showing the shunt tip in situ with good visualization of sulcul space , suggestive of a well - functioning shunt contrast ct of the abdomen showing the marked ascites in the abdominal cavity csf ascites has been defined as the  accumulation of excess csf within the peritoneal cavity. it is a rare complication of the ventriculoperitoneal ( vp ) shunt . the exact cause of csf ascites is still not clear . on review of literature , various possible mechanisms have been described : i ) excessive csf production in a cases of choroid plexus papilloma may cause csf ascites after vp shunt due to imbalance between csf production and peritoneum absorption . iii ) chronic inflammatory conditions like tuberculosis , peritoneal inflammation by multiple shunt revisions , or allergy to shunt material decrease the absorptive capacity of peritoneum , leading to csf ascites . iv ) csf ascites has also been reported in optic nerve gliomas and in craniopharyngioma . [ 812 ] v ) in brain tumors , especially in astrocytoma , increased vascular permeability can cause microvascular extravasation of plasma into the peritoneal cavity and cause ascites . despite all these postulated mechanisms , no satisfactory explanation has been given to date , and most of the reported cases have unknown etiology . holoprosencephaly is a birth defect that occurs during the first few weeks of intrauterine life . there is incomplete or absent division of the embryonic forebrain ( prosencephalon ) into distinct lateral cerebral hemispheres . variable degrees of facial deformities , mental retardation , epilepsy , or abnormalities of other organ systems such as the cardiac , skeletal , genitourinary , and gastrointestinal may be present . the reason for hydrocephalus remains unclear in alobar hloprosencephaly , and the formation of csf ascites in our case offers an insight into the possible mechanisms involved in the formation of hydrocephalus in these patients . we hypothesize that that the primary problem lies in excessive csf production , which may be actually excacerbating the holoprosencephaly by preventing the growth of the cortical mantle , besides leading to csf ascites , as seen in our case . the cause of excessive csf production may also have a molecular basis and it may be possible that the genes responsible for causing holoprosencephaly may also be responsible for upregulating the csf production . although we achieved a satisfactory short - term outcome in our patient by upgrading the opening pressure of the shunt valve , this may not be desirable as it may lead to chronic hydrocephalus in these patients . patients with holoprosencephaly can develop hydrocephalus , the etiology of which remains to be elucidated . research into the molecular change which occurs at genetic level may shed light on the etiopathogenesis of hydrocephalus in these patients .
holoprosencephaly is usually associated with microcephaly , although macrocephaly is not uncommonly seen . 
 however , the cause of hydrocephalus in holoprosencephaly remains ill - defined . here 
 , the authors report a case of csf ascites following ventriculoperitoneal shunt placement in a five month - old child with alobar holoprosencephaly , and hypothesize that the excessive csf production which occurs in this condition may be responsible for the formation of csf ascites . 
 further research is required to assess whether the gene responsible for holoprosencephaly is also responsible for upregulating csf production in patients with concomitant hydrocephalus .