Figure 5: Coronal and axial MRI of the newborn head reveals marked enlargement of both occipital horns of the lateral ventricles, agenesis of the corpus callosum, cerebellar hypoplasia, and enlargement of the cisterna magna.
Approximately 36 reports of colpocephaly have appeared in the literature. This figure may be misleading, however, as there is a lack of consensus as to the precise definition of the term colpocephaly.
Most authors appear to agree that the findings of colpocephaly include disproportionate enlargement of the occipital horns, with the remaining ventricular system maintaining normal size and configuration. In addition, most, but not all, authors believe that the condition is associated with partial or complete agenesis of the corpus callosum2.
The debate in the literature centers around the morphogenesis of the process, with some authors viewing it strictly as developmental anomaly3. Others view the term colpocephaly as only being descriptive. They find no inconsistency in using the term to describe isolated occipital ventriculomegaly resulting from destruction of neural elements that had previously been normally formed2.
From the standpoint of antenatal diagnosis, the term should probably be descriptive of isolated occipital ventriculomegaly rather than as a unique clinical entity. This is because, in most cases, the underlying etiology, be it failure of morphogenesis or a destructive process, will not be known.
The lateral ventricles arise as cavities within the telencephalon. The telencephalon gives rise to two diverticula that expand over the diencephalon and mesencephalon to give rise to the cerebral hemispheres. "During the third gestational month, there is formation of the temporal pole and the ventricles are now in a `U" shape4".
The appearance and growth of the occipital ventricular projection takes place between 23 and 34 weeks8.
The normal reduction in diameter of the occipital horns of the lateral ventricles is critically dependent upon correct morphogenesis of the corpus callosum. "The fibers of the corpus callosum, the forceps and the tapetum, the internal parietooccipital fissure, and the calcarine fissure all take part in shaping and reducing the size of the occipital horn4".
The term colpocephaly was originally coined by Yakovlev and Wadsworth, who stated that "in the apparent dilatation of the occipital horns...it represented a failure of development of the cerebral wall with persistence of the embryonal vesicular character of the brain3".
If colpocephaly is the result of abnormal morphogenesis, then any process that inhibits the normal neuronal migration from within the ventricle, and likewise the normal genesis of the corpus callosum, may result in this entity.
Clearly, however, not all patients with agenesis of the corpus callosum manifest isolated ventriculomegaly of the occipital horns. Therefore, the precise pathogenesis of this process remains incompletely explained.
Colpocephaly has been associated with chromosomal anomalies such as trisomy 8 mosaic5 and trisomy 9 mosaic2. Infectious associations have included gestational exposure to Toxoplasma gondii2. Maternal gestational ingestion of ethanol, oral contraceptive medications, dipropion hydrochloride (Tenuate®), and doxylamine succinate (Bendectin®) have been reported in association with colpocephaly2. Colpocephaly has been described in conjunction with Pierre-Robin syndrome6.
Associations such as those listed above must be viewed with caution, however, as timing, duration, and quantity of exposure are rarely reported in the literature.
In cases not associated with chromosomal aberration, extra-cranial anomalies have included cleft palate and chorioretinal coloboma4. Associated intracranial anomalies have included microcephaly, agenesis of the corpus callosum, meningomyelocele6, optic nerve atrophy, lissencephaly7, periventricular leukomalacia, enlargement of the cisterna magna and cerebellar hypoplasia6.
Antenatal diagnosis is made with the demonstration of enlargement of either or both occipital horns of the lateral ventricles. The atria may be enlarged as well. The remainder of the ventricular system should have normal dimensions and configuration. To meet the criteria established by Yakovlev, partial or complete agenesis of the corpus callosum should be noted as well.
A wide range of neuro-developmental outcomes has been reported in the presence of colpocephaly2. Perhaps this is because of uncertainty as to the exact etiology of the process.
Of 36 cases reported in the modern literature, 13 patients had seizures. Twelve patients were noted to have mental retardation. Thirteen of 36 cases were affected by mild to severe movement disorders. Other reported outcomes include poor vision, speech and language difficulties, deafness, and chorioretinitis.
Three of the 36 cases reviewed had completely normal neurologic and motor development2-6.
Antenatal diagnosis of colpocephaly should prompt a search for underlying associations such as karyotypic abnormalities. In addition, maternal exposure to viral or parasitic pathogens should be considered. Finally, maternal ingestion of medication or toxic substances should be evaluated.
In the absence of macrocephaly, there should be no contraindication to vaginal delivery.
1. Benda CM: Microcephaly. Am J Psychol 97:1135-46, 1984.
2. Landman J, Weitz R, Dlitzki F, et al.: Radiological colpocephaly: a congenital malformation or the result of intrauterine and perinatal brain damage? Brain Dev 11:313-6, 1989.
3. Yakovlev PI, Wadsworth RC: Schizencephalies: a study of the congenital clefts in the cerebral mantle. I. Clefts with fused lips. J Neuropathol Exp Neurol 5:116-30, 1946.
4. Garg BP: Colpocephaly, an error of morphogenesis? Arch Neurol 39:243-246, 1982.
5. Herskowitz J, Rosman P, Wheeler CB: Colpocephaly: clinical, radiologic, and pathogenetic aspects. Neurology 35:1594-8, 1985.
6. Noorani PA, Bodensteiner JB, Barnes PD: Colpocephaly: frequency and associated findings. J Child Neurol 3:100-104, 1988.
7. Krawinkel M, Steen HJ, Terwey B: Magnetic resonance imaging in lissencephaly. Eur J Pediatr 146:205-208, 1987.
8. Nyberg DA, Pretorius DH: Cerebral malformations. in Nyberg DA, Mahony BS, Pretorius DH (Eds) Diagnostic Ultrasound of Fetal Anomalies. Mosby Year Book, St. Louis, pp83-145, 1990.