Craniofacial Dysmorphia of Frontal Proboscis in Holoprosencephaly

Abstract

We have examined eleven cases of holoprosencephaly with special emphasis on the frontal proboscis. Although the nostril appears blind ended grossly, the proboscis has a single slender midline nostril lined with squamous mucosa containing numerous sebaceous glands. It is actually connected to a poorly formed but definite nasal cavity microscopically. The inner portion of the nostril tunnel is lined by olfactory mucosa containing numerous subjacent secretary glands. Despite the absence of olfactory bulbs and tracts the cartilaginous nasal capsule is identified along with abnormal nasal cavity. However, the nasal capsule is hypoplastic, and has an aberrant nasal septum and no concha. In severe form of holoprosencephaly, i.e., cyclopia, the nasal capsule is noted above the level of the ethmoid plate, in which case the nasal cavity dose not communicate with nasopharynx because it is too distant from the hypoplastic maxilla. Therefore, choanal atresia is resulted. Although unique maxillary bone comprises the whole upper jaw, the failure of fusion between vomeronasal septum and palatal processes in holoprosencephaly results in abnormal maxillary bone which is characterized by a narrow palate without palatal arch form. Nevertheless, through serial microscopic sections we could find a space between the posterior maxilla and the sphenoid bone, which is composed of adipose tissue and is similar in shape to the nasal capsule. This space is thought to be made for the nasal capsule during early developmental period. The present study suggests that the frontal proboscis in holoprosencephaly is an undescended nose. In most cases it is connected to the aberrant nasal cavity which is located beneath the proboscis. The level of proboscis descends gradually toward normal nose position as the severity of holoprosencephaly decreased from cyclopia, ethmocephaly, cebocephaly, to premaxillary agenesis. Key words: frontal proboscis, holoprosencephaly, craniofacial dysmorphia