A CASE REPORT OF HEMIMEGALENCEPHALY

K MRAIDHA, S JERBI OMEZZINE, N CHOUCHENE, Z KHADIMALLAH, A ACHOUR, R BOSSOFFARA1, MT Sfar1, HA HAMZA.Department of Medical Imaging, University Hospital Tahar Sfar, Mahdia, Tunisia 1Department of Pediatrics, University Hospital Tahar Sfar, Mahdia, Tunisia

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INTRODUCTION

Hemimegalencephaly  or unilateral

megalencephaly  is a severe, rare

malformation of cortical development ,

characterized by enlargement of all or

parts of a cerebral hemisphere.

The affected hemisphere may have focal or

diffuse neuronal migration defects, with

areas of polymicrogyria, pachygyria, and

heterotopia.

INTRODUCTION

The etiology of this condition is unknown,

though it is speculated that it involves

abnormalities of neuronal differentiation and

cell migration in a single hemisphere.

MR imaging is the imaging technique of

choice for diagnosis of this condition.

We report the following case to illustrate the

MR imaging features of this uncommon but

major congenital malformation of the brain .

HISTORY

A 6-year-old girl with intractable

epilepsy ,

The electroencephalography shows

ipsarythmie,

Magnetic resonance (MR) imaging of

the brain was performed for this girl

.

IMAGING FINDINGS

Abnormal T2 hypointensity of the subjacent white matter with enlargement of the lateral ventricle

IMAGING FINDINGS

Axial Fair weighted MR image revealed pachygyria and right cortical thickening.

IMAGING FINDINGS

Axial diffusion tensor image shows hyper myelination in the white matter of the right anterior frontal lobe.

DISCUSSION

Hemimegalencephaly is a rare congenital

disorder in which there is hamartomatous

overgrowth of all or part of a cerebral

hemisphere.

Described for the first time by Sims in

1835 after reviewing 253 autopsies.

DISCUSSION

The affected hemisphere may have

focal or diffuse neuronal migration

defects, with areas of

polymicrogyria, pachygyria, and

heterotopia.

There is three types of

hemimegalencephaly.

Three types of hemimegalencephaly

1. The isolated form, as in our case, occurs as a sporadic disorder without hemicorporal hypertrophy or cutaneous or systemic involvement.

2. The syndromic form is associated with other diseases and may occur as hemihypertrophy of part or all of the ipsilateral body. It has been described in patients with epidermal nevus syndrome, Proteus syndrome, neurofibromatosis type 1, hypermelanosis of Ito, Klippel-Weber-Trenaunay syndrome, and tuberous sclerosis.

3. The third and least common type is

total hemimegalencephaly, in which

there is also enlargement of the

ipsilateral half of the brainstem and

cerebellum.

Clinical

Males and females are equally affected.

Affected patients may have macrocephaly at

birth and in early infancy and often present

with an intractable seizure disorder,

hemiplegia, and severe developmental

delay. Therefore macrocephaly is often the

first presentation at birth.

Clinical

Epilepsy is the most frequent

neurologic manifestation, occurring in

greater than 90% of patients .

Although progressive hemiplegia and

hemianopia are common, some patients

do not have focal motor deficits.

Diagnosis

The diagnosis of hemimegalencephaly can usually be made at cross-sectional imaging.

At CT, asymmetry of the cranium may be evident with enlargement of all or part of a cerebral hemisphere and ipsilateral ventricle. There is often focal, small, or extensive calcification in the white and gray matter, and the white matter may have abnormally low attenuation representing heterotopia and dysplasia of neurons.

Diagnosis

MR is the imaging modality of choice :

• A characteristic finding is straightening of the

ipsilateral frontal horn of the enlarged

ventricle . However, the ipsilateral ventricle

may be small in some patients. At MR imaging,

the white matter shows heterogeneous but

frequently high signal intensity and there is

often distinction of areas of agyria,

pachygyria, and/or polymicrogyria.

Diagnosis

• The white matter of the affected hemisphere may show advanced myelination for age. There is a roughly inverse relationship between the severity of the cortical and white matter abnormalities and the size of the cerebral hemisphere.

• Patients with agyria tend to have mild to moderate hemispheric enlargement, while those with polymicrogyria have more severe hemispheric enlargement.

Diagnosis

Functional imaging with positron

emission tomography has had good

correlation with CT and MR imaging

findings and has disclosed

functionally abnormal brain regions

in the noninvolved hemisphere that

appeared structurally normal at CT

and MR imaging.

Treatment

Hemispherectomy was first performed for

treatment of refractory epilepsy in 1978 and is

considered the best therapeutic choice for

patients with intractable seizures.

Anatomic or functional hemispherectomy has

also been performed with improvement in

quality of life. Nevertheless, there is a high

mortality and morbidity rate associated with

hemispherectomy.

CONCLUSION

Hemimegalencephaly is a major

congenital malformation of the

brain and MRI is the imaging

modality of choice for the diagnosis

showing unilateral cortical

thickening involving all or part of

the cerebral hemisphere as most

notable characteristic.

REFERENCES

David D. Broumandi, MD. Ulrike M. Hayward, MD.James, M. Benzian, MD.Ignacio Gonzalez, MD.Marvin, D. Nelson, MD. Hemimegalencephaly, RadioGraphics 2004; 24:843–848.

N. Sato, A. Yagishita, H. Oba, Y. Miki, Y. Nakata, F. Yamashita, K. Nemoto, K. Sugai, M. Sasaki. Hemimegalencephaly: A Study of Abnormalities Occurring Outside the Involved Hemisphere, J Neuroradiol 28:678–82 Apr2007.

H. Kometani. Postnatal evolution of cortical malformation in the ‘‘non-affected” hemisphere of hemimegalencephaly, Brain & Development 32 (2010).