Fig. I . Non-contrast CT at 4% months, showing left hemimegalencephaly with frontal cortical thickening, pachygyria and dilatation of left lateral ventricle.

surgery, but none thereafter. The hemiparesis resolved after the operation. Four months post-hemispherectomy he is seizure-free, and is receiving vigabatrin (7Smg/kg/day) and phenobarbitone. He feeds normally, moves all four limbs symmetrically, smiles to voices and is beginning to f ix and follow visual cues. Head growth remains parallel to the 98th centile.

Macroscopically, only the temporal lobe showed gyri and an obvious sulcal pattern. Microscopic examination demonstrated a grossly abnormal neocortex with an almost complete lack of normal neuronal architecture. There was a distinct superficial cortical layer, containing grossly abnormal and giant neurons.

Hemimegalencephaly is characterised clinically by severe epilepsy, psychomotor retardation and hemipare~is‘.~. Our patient developed frequent drug- resistant seizures from the first week of lge, and made no developmental progress. Investigations indicated that the right hemisphere was ‘normal’ and exluded the presence of seizures originating from that hemisphere. A left hemispherectomy was performed to treat intractable epilepsy, and also in the hope of allowing development of higher cortical functions in the right 2 74

hemisphere. Seizures may yet develop in the right hemisphere2; however, the child is currently seizure-free and has made some developmental progress. While it is right to strive for medical control of seizures4, we feel that delaying surgery for too long may limit, or even prevent, psychomotor development.

RICHARD APPLETON* DAVID GARDNER-MEDWIN

DAVID MENDELOW Departments of Paediatrics (Neurology),

Newcastle General Hospital, Westgate Road, Newcastle upon Tyne NE4 6BE. *Child Development Centre, Royal Liverpool Children’s Hospital, Alder Hey, Liverpool L I2 2AP.

and Neurosurgery,

References 1. King, M., Stephenson, J. B. P., Ziervogel, M.,

Doyle, D., Galbraith, S. (1985) ‘Hemimegalen- cephaly-a case for hemispherectomy?’ i euro- pediatrics, 16, 46-55.

2. Vigevano, F., Bertini, E., Boldrini, R., Bosman, C., Claps, D., di Capua, M., di Rocco, C., Rossi, G. F. (1989) ‘Hemimegalencephaly and intractable epilepsy: benefits of hemispher- ectomy.’ Epilepsia, 30, 833-843.

3. Tjiam, A. T., Stefanko, S., Schenk, V. W. D., de Vlieger, M. (1978) ‘Infantile spasms associated with hemihypsarrhythmia and hemimegalen- cephaly.’ Developmental Medicine and Child Neurology, 20, 779-789.

4. Trounce, J. Q., Rutter, N., Mellor, D. H. (1991) ‘Hemimegalencephaly: diagnosis and treatment .’ Developmental Medicine and Child Neurology, 33, 261-266.

How Idiopathic is Idiopathic External Hydrocephalus?

SIR- The report by Cundall et a1 . ’ on identical twins with idiopathic external hydrocephalus and their proposal of a monogenic inheritance of the trait is of particular interest, because it induces refection about the possible pathogenic mechanisms of this clearly hetero- geneous condition. We would like to recount our own observations, with data from the literature relevant to idiopathic external hydrocephalus.

with hypodense subarachnoid fluid collections, we found that only 12 had an uneventful delivery (Table I). In three a primary neonatal subarachnoid

In a series of 3 I macrocephalic infants

haemorrhage had been documented by CT scan. This type of intracranial bleeding may frequently go undetected in the neonatal period2, although it is often confirmed by CT scan after birth asphyxia and/or difficult vacuum extraction3. Others have observed the condition after perinatal trauma or hypoxia4 and after periventricular bleeding’.

hydrocephalus with macrocephaly has been linked to either abnormal circulation or deficient resorption of cerebrospinal fluid, as shown with isotope cisternography or invasive testing of CSF dynamics6-”.

subarachnoid bleeding, with the ensuing transient disturbance of circulation, should be precluded as a causal factor before a monogenic cause can be accepted. In the incidental CT documentation of enlargement of the subarachnoid spaces in both a macrocephalic parent and child, neither information on perinatal events nor on liquor circulation was available’.

Alternatively, external hydrocephalus may be explained by an increased difference in hydrostatic pressure between the intracranial venous sinuses and the fluid in the arachnoid space. This difference is the main, if not the only, mechanism governing transcellular passage of CSF across the arachnoid membrane”. Such a mechanism has been documented in several cases of in fantile external hydrocephalus6, I2-I4 .

Cerebral and meningeal congestion are known to occur in infants with congenital heart disease‘=. We documented macrocephaly caused by external hydrocephalus in several infants with tetralogy of Fallot (Fig. 1). This has also been reported in infants with circulatory complications following the Mustard surgical procedure for transposition of the great arteries16. One can but wonder to what extent an incracranial hydrostatic pressure gradient, as a consequence of patent ducti arteriosi, symptomatic from the age of eight days and ligated at six months, may have contributed to Cundall’s findings’.

For some time now, infantile external

Undetected or undetectable

Fig. 1. Uncontrasted CT scan in 10-month-old boy with tetralogy of Fallot: spontaneous intravascular opacities, hypodense extracerebral fluid collections.

TABLE I Chronic subarachnoid collections in 31 macrocephalic infants

c - E

9 : 8 z

Sex (m:f) 2 4 3

Presenting symptoms (N = 31) Gestational age 2 3 7 wks 21

Macrocephal y 13 Seizures 7 Intracranial hypertension 11 Focal neurological signs 2

From birth 1 In at least one parent 9

Spontaneous vaginal 12 Precipitate 4 Delay in second stage 1 Vacuum extraction 9 Forceps extraction 2 Secondary caesarean section 3

CT scan 3 Disturbed isotope cisternography 1

Macrocephaly

Delivery (N = 30)

Neonatal subarachnoid haemorrhage on

Although ‘idiopathic’ external hydrocephalus as an autosomal dominant, variant trait is a tempting and heuristic hypothesis, it must be pointed out that at least nine of the 31 infants listed in Table I had one parent with occipitofrontal circumference (OFC) at or above the 90th centile. This is not significantly different from the 2 75

six expected, assuming that OFC is a normally distributed trait in the population. On this basis, the probability for any child to have at least one parent with an OFC at or above the 90th centile is 2(1/10 x 9/10) + (I/IO x 1/10), or 19 per cent. Simple autosomal dominant inheritance cannot explain the considerable male preponderance among patients with in fantile external hydrocephalus (around 70 per cent). Therefore, male-limited or preferential expression should become an additional prerequisite, to explain the uneven sex distribution evident from the literature, as well as our own data (Table I).

‘essential or idiopathic’ familial macrocephaly should be diagnosed only when megalencephaly, likely to be present from birth, has been documented with ultrasound or CT scan both in parent(s) and child(ren), without neurological disorder but with enlarged head circumference. An effort should be made to exclude external hydrocephalus in infancy, as defined by recent reports” ‘9. Genuine cases of hereditary disturbance of the liquor circulation, as proposed by Cundall et d.’, should be documented by a study of CSF dynamics, both in the children and parents. One should not try to diagnose ‘idiopathic familial macrocephaly ’ (McKusick 1534 7) without a careful study of the perinatal history.

In conclusion, we propose that

PAUL GOVAERT, M.D. ANN OOSTRA, M.D.

DIRK MATTHYS, M.D. PIET VANHAESEBROUCK, M.D.

JULES LEROY, M.D., Ph.D. Department of Paediatrics and

University Hospital Gent, De Pintelaan 185, B 9000 Gent, Belgium

References

Neonatal Medicine,

1. Cundall, D. B., Lamb, J. T., Roussounis, S. H. (1989) ‘Identical twins with idiopathic external hydrocephalus. ’ Developmental Medicine and Child Neurology, 31, 678-681.

2. Volpe, J. J. (1987) Neurology of the Newborn. Major Problems in Clinical Pediatrics, Vol. 22.

Philadelphia: W. B. Saunders. pp. 292-294. 3. Govaert, P., Van De Velde, E.,

Vanhaesebrouck, P., De Praeter, C., Leroy, J. G. (1990) ‘CT diagnosis of neonatal sub- acrachnoid hemorrhage. ’ Pediatric Radiology,

4. Rothenberger, A., Brandl, H. (1980) ‘Subdural effusions in children under two years: clinical and computer-tomographical data.’ Neuro- pudiatrie, 11, 139-150.

5 . Ment, L. R., Duncan, C. C., Guhr, R. (1981) ‘Benign enlargement of the subarachnoid spaces in the infant.’ Journal of Neurosurgery, 54, 504-508.

6. Portnoy, H., Croissant, P. (1978) ‘Megalen- cephaly in infants and children.’ Archives of Neurology, 35, 306-316.

7. Robertson, W. C., Chun, R. W. N., Orrison, W., Sackett, J . P. (1979) ‘Benign subdural collections of infancy.’ Journal of Pediatrics,

8. Caldarelli, M., Di Rocco, C., Rossi, G. F. (1979) ‘Lumbar subarachnoid infusion test in paediatric neurosurgery.’ Developmental Medicine and Child Neurology, 21, 71-82.

9. Tsubokawa, T., Nakamira, S., Saton, K. (1984) ‘Effect of temporary subdural peritoneal shunt in subdural effusion with subarachnoid effusion.’ Child’s Brain, 11, 47-59.

10. Gooskens, R. H., Willemse, J., Gielen, C. C. (1985) ‘Cerebrospinal fluid dynamics and cerebrospinal fluid infusion in children. Part 11: Clinical application of lumbar cerebrospinal fluid infusion in children with macrocephaly and normal growth rate of the head circumference. Neuropediatrics, 6,

11. Gomez, D. G., Potts, D. G. (1977) ‘Effects of pressure on the arachnoid villus. ’ Experimental Eye Research, 25 (Suppl.), 117-125.

12. Hooper, R. (1961) ‘Hydrocephalus and obstruction of the superior vena cava in infancy.’ Pediatrics, 25, 192-799.

13. Kendall, B., Holland, I. (1981) ‘Benign communicating hydrocephalus in children.’ Neuroradiology, 21, 93-96.

14. Sainte-Rose, C., Lacombe, J., Pierre-Kahn, A., Renier, D., Hirsch, J. P. (1984) ‘Intracranial venous sinus hypertension: cause or consequence of hydrocephalus in infants?’ Journal of Neurosurgery, 60, 727-736.

15. Cohen, M. M. (1958) ‘The central nervous system in congenital heart disease.’ Neurology, 8, 452-456.

16. Sweeney, M. F., Bell, W. E., Doty, D. B., Schilken, R. M. (1982) ‘Communicating hydrocephalus secondary to venous compli- cations following intraatrial baffle operation (Mustard procetlure) for d-transposition of the great arteries. Pediatric Cardiology, 3,

17. Govaert, P., Pauwels, W., Vanhaesebrouck, P., De Praeter, C., Afschrift, M. (1989) ‘Ultrasound measurement of the subarachnoid space in infants.’ European Journal of Pediatrics, 148, 412-413.

18. Alvarez, L. A., Maytal, J., Shinnar, S. (1980) ‘Idiopathic external hydrocephalus: natural history and relationship to benign familial macrocephaly.’ Pediatrics, 77, 901-907.

19. Gooskens, R. H. J. M., Willemse, J., Faber, J. A., Verndonck, A. F. M. M. (1989) ‘Macro- cephalies. A differentiated approach.’ Neuro- pediatrics, 20, 164-169.

20, 139-142.

94, 382-385.

121-125.

237-240.

276