Alobar Holoprosencephaly

Holoprosencephaly is a complex intracranial abnormality characterized by absent or incomplete cleavage of the Prosencephalon (1).From a genetic point of view all holoprosencephalies have the same significance. Their frequency is estimated at 1 in 16,000 to 1 in 18,000 births (2).Holoprosencephalies have a heterogenous cause; chromosomal aberration is found in about one half of the cases. Chromosome 13 is most frequently involved. Partial deletion of chromosome 13 as well as trisomy may coexist with Holoprosencephalies. (2) Holoprosencephaly as, an autosomal dominant inheritance is rare but certainly exists. Recurrence risk after an isolated case of holoprosencephaly with normal chromosome is 5-6% (3).During the fourth gestational week, the neural tube forms three primary brain vesicles: the prosencephalon, mesencephalon and rhombencephalon. During the fifth week the forebrain (Prosencephalon) further divides into secondary vesicles: the telencephalon and diencephalons. Partial division of the telencephalon into two cerebral hemisphere occurs by the end of the fifth fetal week. Complete or partial failure in division of the developing cerebrum (Prosencephalon) into hemispheres and lobes results in the Holoprosencephalies. (4)Alobar form is rare malformation consisting of large Holospheric Brain. Alobar holoprosencephaly is characterized by nearly complete lack of ventricular and hemispheric cleavage. The Brain is basically an undifferentiated Holosphere with central monoventricle and fused thalami (4). 17% cases of Holoprosencephaly are reported with no facial anomaly (5).



Reference

Macahan PJ, Nyberg AD, Mack AL. Sonography of facial feature of alobar and semi lobar Holoprosencephaly. AJR, 1990:154:143-148.

Barness EG.Prosencephalon Growth Failures. Potter's Pathology of the Foetus And Infants.3rd Ed: Vol 2:Mosby: 1997:1056-1059.

Baraister M, Winter RM. Holoprosencephaly.Color atlas of Congenital Malformation Syndrome.Mosby: 1996:148.

Osborn AG. Disorders of Diverticulation and Cleavage, Sulcation and Cellular Migration. Diagnostic Neuroradiology.1st Ed: Vol 1:Mosby, 1994:37-39.

Dahnert WG, Radiology Review Manual. 3rd Ed: Williams &Wilkins, 1996:213-214.



Ind J Radiol Imag 2003 13:3:295-296