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NEURORADIOLOGY HEAD AND NECK IMAGING Table of Contents   
Year : 2002  |  Volume : 12  |  Issue : 2  |  Page : 197-200
External hydrocephalus in children


Department of Imaging and Interventional and Radiology, Institute of Neurological Sciences, Guwahati-781006, India

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Keywords: External hydrocephalus, macrocephaly

How to cite this article:
Handique S K, Das R R, Barua N, Medhi N, Saharia B. External hydrocephalus in children. Indian J Radiol Imaging 2002;12:197-200

How to cite this URL:
Handique S K, Das R R, Barua N, Medhi N, Saharia B. External hydrocephalus in children. Indian J Radiol Imaging [serial online] 2002 [cited 2014 Sep 1];12:197-200. Available from: http://www.ijri.org/text.asp?2002/12/2/197/28442
External hydrocephalus (EH) is a condition that is characterized by enlargement of the subarachnoid spaces in an infant with macrocephaly [1]. The enlarged subarachnoid spaces are typically seen in the frontal areas and interhemispheric fissures. The sylvian fissures may be widened. Ventricular enlargement is usually absent or may be mild to moderate if present. It is usually a self-limited condition that presents between ages of 3 to 12 months and resolves spontaneously. Psychomotor development may be normal or delayed.

We report three patients with this condition. Diagnosis was established on the basis of clinical features of macrocephaly (Head circumference above 90th percentile) with enlarged extracranial cerebrospinal fluid (CSF) spaces and mild ventriculomegaly. In all of them follow up CT or MRI revealed reduction of the extracerebral collection and ventriculomegaly. One had family history of macrocephaly. The other two were idiopathic. Two had delayed motor development, one had severe delay in motor development up to three years of age. In one patient, spontaneous subdural hematomas were seen


   Case Discussion Top


Case 1

A 13 month old boy was brought to us with history of 3 episodes of seizures. His parents had noticed that his head was progressively increasing in size. His motor milestones were delayed. Examination revealed a head circumference (HC) of 53 cm. Hypotonia of the skeletal muscles was noted. Initial MR [Figure - 1]a and b revealed prominent frontal and parietal subarachnoid cerebrospinal fluid (CSF) spaces. The sylvian fissures were prominent. Mild ventricular enlargement was noted. Bilateral frontoparietal subacute T1 hyperintense subdural hematomas were noted. He was started on anticonvulsants and followed up on 2-3 months intervals. Follow up MR at 23 months revealed mild residual left frontal subdural hematoma. The frontal and parietal CSF spaces were now small in size. The sylvian fissures were still dilated and ventriculomegaly was the same. A CT scan done at 3 yrs of age [Figure - 1]c revealed proportionately smaller ventricles and frontal CSF spaces. The sylvian fissure showed slight reduction in size. The elder sister of this patient aged 6 years also had an enlarged head since infancy. She had mild psychomotor developmental delay but no seizures. MR revealed normal frontal CSF spaces but large sylvian fissures. Multiple members of the family had large heads both on the paternal and maternal sides however only some of them had seizures. At his last check up at 3 years of age he still had disabling motor delay and hypotonia but had no seizures. The head showed no further enlargement (HC = 53cm).

Case 2:

A 5 months old male infant was brought to our Institute primarily for gradual increase in size of the head. His motor milestones were minimally delayed. He had occasional fever. On examination his head circumference was 45cms. The anterior fontanelle was bulging and tense. Coronal and parietal sutures were not yet closed. No other abnormality was noted.

MR [Figure - 2]a revealed prominent bifrontal, temporal and parietal CSF collections. The third and lateral ventricles showed mild dilatation. The sylvian fissures were prominent. The child was kept under follow up. On a subsequent visit at 11 months of age, the head circumference was 48cm. Developmental milestones were normal. A CT scan [Figure - 2]b done at this time showed proportionally mild reduction in the size of the extracerebral CSF collections.

Case 3:

A 10 month old boy was brought to us with a history of trivial head injury. On examination the child was fully conscious and had no neurologic deficit. The baby had an enlarged head (HC=50.5cm.) with tense fontanelle and the parents on questioning said that his head was gradually enlarging since birth. He was delivered after a full term pregnancy by cesarian section. His developmental milestones were normal. CT revealed mild ventricular dilatation with enlarged fronto-parietal CSF spaces especially on the left side [Figure - 3]a. The patient was kept under diamox therapy. A follow up exam at age 13 months showed normal motor development. The HC was now 52cm and fontanelle almost closed. A CT scan done at this time showed reduction in ventricular size and the extracerebral CSF collection [Figure - 3]b. At his last check up at age 18 months there was no further increase in size of the head and his motor and mental development were normal.


   Discussion Top


Known by various other names such as benign external hydrocephalus, benign extraaxial collections of infancy, benign communicating hydrocephalus, idiopathic pericerebral swelling, this condition was first described by Walter Dandy [2] who first introduced the term "external hydrocephalus". Robertson and Gomez [1] in 1978 first described its radiological (CT and pneumoencephalographic) findings.

EH is thought to be caused by defective reabsorption of CSF at the arachnoid villi. This causes CSF pooling in the subarachnoid spaces adjacent to the arachnoid villi, namely over the cerebral convexities. In an infant whose sutures are open, the cranium enlarges to allow considerable amount of CSF to collect in these spaces rather than in the ventricles which are connected to these spaces by a narrow and long cerebral aqueduct. If this succeeds in reducing the CSF pressure, the ventricles do not dilate. However if the drainage is severely affected, the pressure is transmitted to the ventricles which then dilate [1].

Although most cases are idiopathic, various authors have reported association with prematurity, trauma, subarachnoid, subdural or intraventricular hemorrhage, meningitis, vitamin A deficiency and genetic syndromes. Idiopathic EH is generally a benign, self-limited condition that presents between the ages of 3 and 12 months and resolves spontaneously by 2-3 years of age. Because of the good prognosis, surgical intervention is rarely required. Only in those patients who experience gross motor delay, rise in intracranial pressure or huge collections, ventriculoperitoneal shunting may be necessary [3].

EH is characterized on CT and MRI by prominent widening of the subarachnoid spaces in the frontal or frontoparietal regions. The anterior interhemispheric fissure, sylvian fissures and sometimes the basal cisterns are widened. Ventriculomegaly if present is mild to moderate. EH is often confused with cerebral atrophy, but the latter shows diffuse sulcal prominence without localization in the frontoparietal regions. A careful clinical history of an enlarging head helps distinguish this condition as widened frontal CSF spaces may be a normal variant in infants with normal head circumference [4].

In one study of idiopathic EH delayed motor development and hypotonia was found in as many as 30%. High rates of familial forms and severity of complications like spontaneous subdural hematomas (12%) and permanent neurological impairment in some (2/5) were found in this study. This had led the authors to question the benignity of this syndrome whose long term outcome, particularly in terms of cognitive function is still unknown [5].

EH may therefore not always follow a benign course. However most of the time it is a self-limiting condition with spontaneous resolution by 2-3 years of age. Awareness of the imaging findings of this condition together with careful history taking will prevent missed diagnosis.

The authors wish to thank Prabir Bhattacharjee, Dr Himadri Das and Paresh Sarma for help in preparing this article.

 
   References Top

1.Robertson, Jr WC, Gomez MR. External hydrocephalus. Early finding in congenital communicating hydrocephalus. Arch Neurol 1978;35: 541-544.  Back to cited text no. 1    
2.Dandy WE. Extirpation of the choroids plexus of the lateral ventricles in communicating hydrocephalus. Ann Surg 1918; 68: 569= 579.  Back to cited text no. 2    
3.Cinnamon J, Sharma M, Gray D, Greenberg R, Hyman R. A. Neuroimaging of meningeal disease. Seminars in US, CT and MRI 1994; 15: 466 - 498.  Back to cited text no. 3    
4.Odita JC. The widened frontal subarachnoid space. A CT comparative study between macrocephalic, microcephalic and normocephalic infants and children. Childs Nervous System 1992; 8: 36-39.  Back to cited text no. 4    
5.Azais M, Echenne B. Idiopathic pericerebral swelling (External hydrocephalus) of infants. Annales de Pediatrie 1992: 550 - 558.   Back to cited text no. 5  [PUBMED]  

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Correspondence Address:
S K Handique
Department of Imaging and Interventional and Radiology, Institute of Neurological Sciences, Guwahati-781006
India
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    Figures

[Figure - 1], [Figure - 2], [Figure - 3]

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