Review Article Nepal Journal of Neuroscience 2020;17(1):5-9 Gopal Sedain MCh Hydranencephaly: Insights Associate Professor, Department of Neurosurgery Institute of Medicine into Pathophysiology and Maharajgunj Medical Campus, Kathmandu, Nepal ORCID iD: https://orcid.org/0000-0002-8184-3303 Management Binod Rajbhandari MCh Abstract Clinical Lecturer, Department of Neurosurgery Hydranencephaly is a rare and severe form Institute of Medicine of congenital disorder in which there is absence Maharajgunj Medical Campus, Kathmandu, Nepal of cerebral cortex which is replaced by fl uid. The ORCID iD: https://orcid.org/0000-0002-4165-8584 presentation is in the form of hydrocephalus and Address for correspondence: developmental delay. There are various reports on Dr. Gopal Sedain possible etiopathogenesis and management. However, Associate Professor, Department of Neurosurgery the overall prognosis is grim and clinicians especially Institute of Medicine in low and middle-income countries like Nepal Maharajgunj Medical Campus, Kathmandu, Nepal often face a clinical judgement dilemma regarding E-mail: [email protected] management options to off er to the patient family. Contact number: +977 9849485319 The ethical issue whether to off er cerebrospinal fl uid diversion or not is always there. This review is aimed Date of submission: 31st March 2020 at discussing the various aspects of management of th Date of acceptance: 8 April 2020 this pediatric neurosurgical problem. DOI: https://doi.org/10.3126/njn.v17i1.28336 Key words: Hydranencephaly, Management, HOW TO CITE Sedain G, Rajbhandari B. Hydranencephaly: Insights into Pathophysiology, Prognosis Pathophysiology and Management. NJNS. 2020;17(1):5-9 To access Nepal Journal of Neuroscience Archives, scan QR code: Introduction There may be a rarer form with hemi hydranencephaly.4 Among the series of patients reported in literature, the ydranencephaly (HE) is the term used to describe series described by Adeloye is the largest, involving 15 conditions in which the “encephaly” or brain patients with HE.5 Htissue is almost replaced by “hydro” or water. In Owing to the absence of functional cerebral cortex, its severe form there may be complete absence of cerebral higher mental functions are universally aff ected. Regarding cortex but in many cases a thin rim of non-functional survival, most children die during fi rst year of life but cerebral cortex may be present. The midbrain, cerebellum, survival of patient up to 32 years has been reported.6 thalami, basal ganglia, and choroid plexus are usually not Survival probably depends upon the degree of nursing involved.1 care the patient receives and associated manifestations It is often thought to be due to occlusion of bilateral like epilepsy.3 internal carotid arteries in-utero during second trimester.2 The estimated incidence is around 1 per 10,000 live births.3 Etiopathogenesis However, it is diffi cult to fi nd an accurate incidence due to The condition was fi rst described by Cruveilhier similarity with other conditions like hydrocephalus and in 1835. The term hydranencephaly was probably fi rst holo-prosencephaly. introduced by Spielmeyer in 1905.7 Nepal Journal of Neuroscience, Volume 17, Number 1, 2020 5 Sedain et al Many scientists are of the view that the pathogenesis babies present with seizure or seizure-like episodes and is due to occlusion of bilateral supra-clinoidal Internal irritability. Hearing is usually preserved with cases of carotid artery (ICA) in the early fetal life.8 Absence of sensorineural hearing loss have been reported.17 Although fl ow in ICA on angiography is an evidence in many if one might infer that the presence of seizures connotes the not all patients. In all cases in which blood fl ow in ICA preservation of suffi cient cortex needed for prolonged is seen, it is hypothesized that the vessels might have survival, it is more likely that these episodes are primarily probably recanalized after the damage was infl icted. a brainstem-release phenomenon.18 Certain behaviors like Another evidence is the relative preservation of a portion yawning, crying, smile as well as turning head to sound or of brain supplied by the posterior cerebral arteries. Many painful stimuli can occur which are presumably related to patients are seen to have some preservation of occipital refl exes associated with brainstem or diencephalon, rather lobe structures. It is diffi cult to explain the presence of than cortical function.19 fronto-basal cortex in some patients, however, according to some authors, the ophthalmic arteries, which are direct anastomoses between the external and internal carotid arteries, might partially supply these regions during early internal carotid artery occlusion.8 The ICA occlusion probably occurs early during 8 to 12 weeks of gestation as suggested by absence of the carotid canals in patients and preservation of falx. The loss of blood fl ow probably leads to necrosis of brain matter and encephalomalacia replacing it with CSF. 6 Other possible etiology includes intrauterine infection like CMV, toxoplasmosis, rubella etc. leading to massive brain necrosis and cavitation.9,10 R egarding genetic link up, most patients have an unremarkable karyotype. However, triploidy (XXY) has been seen in some patients.6 Toxic exposures, such as cocaine abuse, sodium valproate and smoking have also been reported. HE has been associated with young maternal age and has been described in association with rare syndromes 11,12,13,14. HE has also been seen in monochorionic twin pregnancies, in which the death of one twin provoked a vascular exchange Figure 1: Six months old girl with large head suggesting to the living twin through the placental circulation and may hydrocephalus have caused hydranencephaly in the surviving fetus.15,16 Clinical Presentation In pregnancy there are no abnormal clinical features like decreased fetal movements. Most of the infants are born with a normal head size which keeps on increasing with time or even a normal size. (Figure 1) The choroid plexus continues to produce CSF but the absorption mechanism is ill developed. 4 Many aff ected children die in-utero. Neurological or clinical signs may not be evident at birth; leg and arm movements as well as sucking and swallowing refl exes may be present. However, subtle signs, like feeble cry, diffi culty with feeding, hypotonia or wide anterior fontanelle may be present. Many kids die before their fi rst Figure 2: Plain CT head showing near absence of cortical birthday. In those who survive long, visual impairment, mantle with remnants in frontal and temporal part spastic diplegia and cognitive delay are seen. Many suggestive of hydranencephaly 6 Nepal Journal of Neuroscience, Volume 17, Number 1, 2020 Hydranencephaly: Insights into Pathophysiology and Management Diagnosis Some hypothesis regarding presence of rostral cortex, Fetal ultrasound can usually diagnose the condition in functioning hypothalamo-pituitary adrenal axis, presence late second trimester. Early diagnosis as early as 12 weeks of EEG activity have not been uniformly accepted. The have been reported. 20 Fetal diagnosis is suspected when circuits necessary for maintenance of temperature, blood there is a large fl uid fi lled cavity without any recognizable pressure, and cardiorespiratory functions are, at least in cortical mantle and thalamus and brainstem structures part, functional in prolonged survivors. 3 protruding in the cavity.8 Although thalamic circuits, considered by some to In infancy, non-contrast Computed Tomography (CT) play a role in consciousness, are more likely to be intact in scan can suggest diagnosis in presence of absent or thin patients with hydranencephaly the patients with prolonged cortical mantle with varying amount of scattered cerebral survival were not reported to have any improvement in cortical matter (Figure 2). Magnetic Resonance Imaging consciousness or awareness. Such prolonged survival (MRI) can help in better understanding the condition. MRI is more likely to be associated with a more preserved reveals an almost total parenchymal absence, replaced by brainstem, aggressive nursing care, or a combination of cerebrospinal fl uid and frequently containing remnants both.3,25 of the occipital area and orbitofrontal regions. The falx Documentation of prolonged survival in infants with is usually present, with the preservation of cerebellar HE has important medical, ethical, and legal ramifi cations. hemispheres, thalamus and brainstem. Magnetic The information is essential for appropriate parental resonance phase contrast images may demonstrate atretic counseling not only about the possibility of prolonged or hypoplastic ICA.21 survival but also for decision-making about medical The diff erential diagnosis of severe hydrocephalus treatment that may prolong survival but ultimately will be and alobar holoprosencephaly need to be ruled out as far futile for improved neurodevelopmental outcome. as possible. Diff erentiating with severe hydrocephalus There are also cases of HE exhibiting a responsiveness may be particularly diffi cult. Hydrocephalus has a better to their surroundings incompatible with the classifi cation prognosis so it is very important to separate these two of vegetative state. 26 entities. In HE, the cortical mantle may be absent unlike There are issues related to the modifi cation of brain in hydrocephalus which has mantle though thinned out. death criteria for purposes of organ procurement for infants Electroencephalogram (EEG) changes may be helpful. with anencephaly, yet