Perinatology Unit, Carabobo University, Valencia -- Venezuela

Synonyms: hypophyseal canal, craniopharyngeal duct, transsphenoidal canal.

Prevalence: very rare.

Definition: Persistence of the craniopharyngeal canal is a rare basal skull congenital defect with a range from small canals (in 0.42% of the asymptomatic population [1] ) to large basal cephalocele with major craniofacial defects. Craniopharyngeal canal represents a remnant of the stem of Rathke's pouch that goes through the sphenoidal synchondrosis between the presphenoid and postsphenoid by a vertical conduct in the basisphenoid, extending from the floor of the sella turcica to the undersurface of this bone and connecting the pituitary fossa with the nasopharynx cavity.

Etiology: unknown, some authors have reported maternal use of anticonvulsants [2] .

Embryology: The adenohypophyseal primordium is induced by the adjacent floor of the forebrain from which the neurohypophysis will develop. The primordium is situated immediately external to the oropharyngeal membrane and becomes a pocket, the adenohypophyseal pouch, at 24 days of gestation. The basement membrane of the pouch appears to be in contact with that of the diencephalon, but cells soon become visible between the two membranes and the pouch becomes discontinuous at its apex. Then over the apex, the floor of the forebrain form an evagination, the stem of the pouch becomes narrowed and loses its connection with the roof of the mouth during the sixth week of embryonic development. The craniopharyngeal canal is a channel formed during osteogenesis and which may persist as a passage through the sphenoid bone. It indicates approximately the course of the former stem of the adenohypophyseal pouch [3] .

This traditional explanation of the origin of adenohypophysis from ectoderm near the stomadeum has been challenged [4] . In birds, there is evidence to suggest that the cells that form Rathke´s pouch are of neuroectodermal origin, arising from the ventral neural ridge [5] , [6] .  Pearse et al advanced the view that this would link the adenohypophysis with other structures derived from the neural crest and make it an integral part of the amine-precursor-uptake-decarboxylation (APUD) system.

Associated anomalies: Arachnoid cyst, cystic pituitary adenoma, anencephaly, holoprosencephaly [7] , craniopharyngioma [8] , Rathke's cleft cyst [9] , cephalocele [10] , meningohydroencephalocele [11] and other anomalies of the skull base.

Prenatal diagnosis: Non-reported before.

Prognosis: it depends on the size of the canal and the associated anomalies. It has been reported upper airways obstruction during infancy, cerebrospinal fluid rhinorrhea, meningitis, sinusitis, panhypopituitarism, accidental removing of the hypophysis mimicking a midline nasal polyp, neurological symptoms, hydrocephaly [12] .

References:

Arey L The craniopharyngeal canal reviewed and reinterpreted. Anat Record 1950; 106:1-16

[2] Currarino G, Maravilla KR, Salyer KE. Transsphenoidal  canal ( large craniopharyngeal canal ) and its pathologic implications. Am J Neuroradiol 1985; 6:39-43.

[3] O'Rahilly R. Müller F. Human Embriology and Teratology. Second Edit. Wiley Liss,Inc. USA. 1996:317-20.

[4] Desa D. endocrine Glands. In Gilbert-Barnes E. Potter's Pathology of the fetus and infant. Mosby Year Book,Inc. USA. 1997:1151.

[5] Takor TT, Pearse A. Neuroectodermal origin of avian hypothalamo-hypophyseal complex. The role of ventral neural ridge. J. Embriol Ex Morphol 1975; 34:311-15.

[6] Pearse A, Takot TT. Embriology of the diffuse neuroendocrine system and its relationship to the peptides. Fed Proc 1979;38:228

[7] Kjaer I, Fisher-Hansen B. Human Fetal Pituitary gland in holoprosencephaly and anencephaly. J Craniofac Genet Dev Biol 1995 Oct; 15(4):222-29

[8] Sosa-Olavarria A, D?az-Guerrero L ,Reigoza A,Berm?dez A, Murillo M. Fetal Craniopharyngioma: early prenatal diagnosis. J Ultrasound Med 2001;20:803-06.

[9] Herzog J, Makek M, Fish U. Lesions of Rathke´s duct: another indication for the infratemporal fossa approach. Otolaryngol Head Neck Surg 1998; 101(3):303-8.

[10] Kjaer I, Russel BG. The craniopharyngeal canal indicating the presence of pharyngeal adenopituitary tissue. Eur J Radiol 1995; 20:212-14.

[11] Durham LH, McKenzie IJ, Miles JB. Transphenoidal meningohydroencephalocele. Br J Neurosurg 1988; 2:407-10.

[12] Hughes ML,Carty AT, White FE. Persistent hypophyseal (craniopharyngeal) canal. Br J Radiol. 1999 ; 72:204-6.