American Journal of Neuroradiology 25:285-288, February 2004
© 2004 American Society of Neuroradiology
Case Report
BRAIN
A Rare Expression of Neural Crest Disorders: An Intrasphenoidal Development of the Anterior Pituitary Gland
Kathlyn Marsot-Dupucha,
Wendy R. K. Smokerb and
Walter Grauerc
a Department of NeuroRadiology, Faculty Paris Sud, le Kremlin-Bicêtre, France
b Department of Radiology, University of Iowa Hospitals and Clinics, Iowa City, IA
c Department of Department of Radiology, Bethanien Spital, Zurich, Switzerland
Address reprint requests and correspondence to Dr. Kathlyn Marsot-Dupuch Bicêtre Hospital-Neuroradiology, 78 rue du Général Leclerc. Kremlin-Bicêtre, France 94 275
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Abstract
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Summary: Congenital abnormalities of the pituitary gland are
rare and may be associated with midline cranial, orbital, and
facial anomalies and with hormonal insufficiency. Here we report
a case of asymptomatic, abnormal migration of the adenohypophysis.
The normally developed adenohypophysis was located in the sphenoid
bone and developed on the intersphenoidal septum, extending
from the superior pharyngeal wall to the floor of the sella
turcica (craniopharyngeal canal). The abnormal migration of
the pituitary gland was isolated without hormonal deficit, brain,
or facial developmental anomalies.
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Introduction
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Migration disorders of the pituitary gland are a rare phenomenon,
almost always reported for the neurohypophysis in patients with
micropituitarism (
1). Migration arrest of the adenohypophysis
in the sphenoid bone is extremely rare, probably because it
is usually asymptomatic. The exact etiology of this anomaly
is not clear but it probably results from vascular, toxic, or
genetic insults occurring during the period of Rathke’s
pouch obliteration (42–45 days of gestational life). As
it migrates with the pharyngohypophyseal pouch, the adenohypophysis
may develop within the sphenoid bone in front of the sphenooccipital
synchondrosis. Moreover, in case of excessive sphenoid pneumatization
(eg, sphenoid pneumatization over the clivus) the ectopic adenohypophysis
may develop within the sphenoid sinus, attached to the sphenoid
septum, presenting as an intrasinus mass.
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Case Report
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A 20-year-old woman was referred to our department for MR imaging
of the brain following a new onset of seizures. Physical examination
was normal. She had no significant medical history. Review of
systems was negative, and she took no medications. Brain MR
documented normal signal intensity and morphology of the brain
parenchyma except for an empty sella turcica. A linear structure
going from the floor of the sella turcica to the inferior wall
of the sphenoid sinus was identified (
Fig 1). A CT examination
of the skull base demonstrated an intrasphenoidal bony canal
8 mm in diameter, extending from the sella turcica to the nasopharynx
and adjacent to the right lateral border of the sphenoid septum
(
Fig 2A and B). Pituitary MR imaging demonstrated normal, intrasellar
high signal intensity of the posterior pituitary gland and a
well-developed pituitary infundibulum inferiorly (
Fig 3A and B).
No anterior pituitary gland was seen within the sella turcica.
The craniopharyngeal canal was filled by tissue of intermediate
signal intensity on both T1- and T2-weighted images (sagittal
sections), which demonstrated intense enhancement similar to
nasal mucosa on dynamic contrast-enhanced sequences. An associated
clival anomaly was present.
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FIG 1. Sagittal T1-weighted image (528/16/2 [TR/TE/NEX]). Note the canal extending from the floor of the sella to the nasopharynx (arrows).
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FIG 2. Axial (A) and sagittal (B) reconstructed CT images through the sphenoid bone. Note the intrashenoidal bony canal (arrows).
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FIG 3. Midsagittal T1- (A, 450/14/2) and B) T2-weighted (B, 550/117/3) weighted MR images. Note the midline canal filled with intermediate signal intensity material on both T1- (A) and T2-weighted (B) images extending from the sella to the nasopharynx. Note the normal location of the pituitary infundibulum (A, arrow) and a small amount of CSF with the upper portion of the canal in (B).
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Because the patient had no hormonal abnormalities, the imaging studies were thought to be most consistent with an ectopic adenohypophysis due to arrest of normal gland migration. The patient had no stigmata of any other developmental anomalies, and inquiry into possible insults occurring in utero did not yield clues. The patient was informed of this developmental anomaly and of the risk it might pose in the event of sphenoid surgery.
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Discussion
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The hypophysis develops from two different origins: one from
an ectodermal outpocketing of the stomodeum, known as Rathke’s
pouch, and the other from a downward extension of the diencephalon,
called the infundibulum (
1). At 3 weeks of gestation, Rathke’s
pouch grows dorsally as the infundibulum grows ventrally. During
the second month of gestational development, the Rathke’s
pouch loses its connection with the stomodeum, and its anterior
part forms the adenohypophysis. The obliteration of Rathke’s
pouch occurs between the 42 and 45 days of gestational life
(
2).
The pituitary gland lies within the boundary between the neural crest cell (NCC)-dependant and NCC-independent portions present the composite sella turcica. At the end of cephalic rotation, both the adenohypophysis and neurohypophysis are located within the sella turcica, separated by the Rathke’s pouch. The embryonic pharyngohypophyseal transsphenoidal (craniopharyngeal) canal is located beneath to the sella turcica, extending between the superior wall of the nasopharynx to the floor of the sella turcica in an oblique fashion (3). It is located within the central sphenoid ossification center, in front of the sphenobasilar synchondrosis (4). This inconstant persistent remnant is termed the craniopharyngeal canal and, in cases of larger defects, "persistent hypophyseal canal" (4). It is observed in approximately 0.42% of the asymptomatic population (3). It may be incomplete, ending blindly without communication with the sella turcica and may contain air if a communication with the pharyngeal lumen exists (3). Its imaging features depend on 1) status of sphenoid bone aeration; 2) status of canal obliteration; and 3) communication with the pharynx (3).
On axial CT sections, the craniopharyngeal canal is located anterior to the lucency of the sphenobasilar synchondrosis (5). It is a midline round foramen with a sclerotic rim. Some air may be present within the canal. On MR images, the low signal intensity of the canal contrasts against the high signal intensity of fatty clival bone marrow (4).
In excessive sphenoid sinus aeration (approximately 5–10% of patients), the craniopharyngeal canal follows the intersphenoidal septum and may, therefore, be located within the sphenoidal sinus, surrounded by the aerated sphenoid cells, sometimes laterally. Moreover, the presence of pituitary tissue within the canal may mimic an intrasphenoidal cystic mass as in the patient. This is correlated to the date of aeration of the sphenoid sinus, which occurs after the pharyngo-hypophyseal canal closure.
Migration and development of the adenohypophysis and neurohypophysis follow two different pathways. It is widely accepted that the epithelial hypophysis has its developmental origin from the extraneural portion of the embryo (ie, the stomodeal ectoderm). But development of adenohypophysal cells requires a good differentiation of the neural crest. Recent works have shown that, in mammalian embryos, the origin of adenohypophyseal cells is before the formation of Rathke’s pouch and adenohypophysis becomes visible at the end of the first month of gestational development (1, 6). Then, the developing pituitary establishes a link to the hypothalamus by the progressive elaboration of the hypophyseal stalk, the median eminence, and the venous portal circulation. By contrast, the posterior hypophysis pinches off from the diencephalon remaining attached by a bridge that will develop into the hypophyseal stalk. All these were normally developed in the reported case.
Migration anomalies are congenital anomalies caused by genetic (neurofibromatosis type 1, trisomy 13), vascular, or environmental insults to migrating neuroblasts (7). The major cell migrational activity lasts approximately 2 months, occurring from 7 to 16 weeks of embryonic life (7, 8). Exposure to ionizing radiation, excessive levels of alcohol (fetal alcohol syndrome), anticonvulsants (phenytoin, barbiturates), or toxic materials (methyl mercury poisoning) may be associated with abnormal neural cell migration (9). Because of the different origins of adenohypophisis and neurohypophysis, an abnormal migration of the pituitary gland involves only the anterior portion of the gland. Arrested migration of the anterior pituitary gland is due to an NCC disorder occurring in utero and probably results from an absence of signal to the epithelial cells during the 2nd month of embryonic life (10). Its occurrence after emergence of neural crest cells explains concomitant normal development of the posterior pituitary gland; the pituitary stalk; the orbital globe; the pituitary vascular system resulting from mesenchymal differentiation; the sphenoid bone, in which the posterior part came from the cephalic mesoderm while the anterior part derived from NCC.
Congenital anomalies of the adenohypophysis may be associated with other midline anomalies such as Chiari type 1 malformation and medial deviation of the internal carotid canal. Associated cortical brain dysplasia was recently reported (2). The association between congenital anomalies of the pituitary gland and breech deliveries is probably related to fetal pituitary hormonal deficiency.
Occasionally, as in our patient, a portion or all of the adenohypophysis may persist in the pathway of the pharyngeal pouch, either in the nasopharyngeal wall or within the sphenoid bone, termed "ectopic intrasphenoidal hypophysis." In this anomaly of adenohypophyseal migration, a well-developed normal neurohypophysis may be located in its normal position (10). Persistence of the craniopharyngeal canal allows nasopharyngeal development of the adenohypophysis. Panhypopituitarism in these instances is probably related to inadvertent hypophysectomy (4, 10, 11).
Moreover, our case demonstrates that large persistent craniopharyngeal canals are not always related to transphenoidal meningocele as some authors postulated (12). Intrasphenoidal ectopic normal functioning pituitary gland was recently reported by Ekinci et al (Table) (4, 11, 13).
If the etiology of the persistence of the craniopharyngeal canal is still not completely clarified, recent works on embryology and presence in normal location of the posterior pituirary lobe and stalk argue against a remnant of a vascular channel. Moreover, trappage of CSF inside this canal without leak as in our reported case may coexist as the pituitary gland is completely enclosed by a dura mater fold except for the aperture of the diaphragma sellae. The craniopharyngeal canal is probably the path of spontaneous CSF leaks and midline meningocele through the sella turcica.
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Conclusion
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A rare anomaly of the adenohypophysis is described with arrested
migration occurring within the sphenoid bone surrounded by sphenoid
cells. The main imaging features are 1) presence of a large
craniopharyngeal canal filled with normal glandular tissue and
CSF; 2) dehiscence of the sella turcica floor; and 3) normal
development of pituitary stalk, portal circulation, and neurohypophysis.
A concomitant, well-developed pituitary vascular network allows
the normal function of ectopic adenohypophysis.
A relationship between the intersphenoidal septum and the path of the adenohypophysis migration is reported. The superimposition in gestational time of the first migration wave and duplicate Rathke’s pouch obliteration supports the contention that the insult causing this anomaly occurs between 42 and 45 days of gestational life. This anomaly testifies that the migration of the neurohypophysis and adenohypophysis are independent.
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References
|
|---|
- Kouki T, Imai H, Aoto K, et al. Developmental origin of the rat adenohypophysis prior to the formation of the Rathke’s pouch.
Development2002; 128
:959
–963
- Blinder G, Corat-Simon, Hershovitz E. Micropituitarism and cortical dysplasia: an unknown association of two uncommon CNS disorders.
Eur Radiol2001; 11
:1070
–1072[Medline]
- Arcy LB. The craniopharyngeal canal reviewed and reinterpreted.
Anat Rec1950; 106
:1
–16[Medline]
- Hughes ML, Carty AT, White FE. Persistent hypophyseal (craniopharyngeal) canal.
Br J Radiol1999; 72
:204
–206[Abstract]
- Jinkins JR. Calvarial foramina variants. In: Jinkins JR, ed.
Atlas of Neuroradiologic Embryology, Anatomy and Variants. Philadelphia: Lippincott Williams and Wilkins;2000
:97
–99
- Etchevers HC, Vincent C, Couly G. Neural crest and pituitary development. In: Rappaport R, ed.
Hypothalamic–Pituitary Development: Genetic and Clinical Aspects. Basel: S. Karger;2001
:13
–29
- Kornreich L, Horev G, Lazar L, et al. MRI findings in growth hormone deficit: correlation with severity of hypopituitarism.
AJNR Am J Neuroradiol1988; 19
:1495
–1499
- Barkovitch AJ, Kjos BO. Gray matter heteropias: MR characteristics and correlation with developmental and neurologic manifestations.
Radiology1992; 182
:493
–499[Abstract/Free Full Text]
- Barkovich AJ, Chuang SH, Norman D. MR of neuronal migration anomalies.
AJNR Am J Neuroradiol1987; 8
:1009
–1017
- Esteban F, Ruiz-Avila I, Vilchez R, et al. Ectopic pituitary adenoma in the sphenoid causing Nelson’s syndrome.
J Laryng Otol1999; 111
:565
–567
- Weber PT, Donnelly WH Jr, Bejar RJ. Hypopituitarism following extirpation of a pharyngeal pituitary.
Am J Dis Child1977; 131
:525
–528[Abstract]
- Kaufmann HH. Nontraumatic cerebrospinal fluid rhinorrhea.
Arch Neurol1969; 21
:59
–63[Medline]
- EkinciG, KilicT, Baltacioglu F, et al. Transsphenoidal (large craniopharyngeal) canal associated with a normal functioning pituitary gland and nasopharyngeal extension, hyperprolactinomia, and hypothalamic hamartoma.
AJR Am J Roentgenol2003; 180
:76
–77[Free Full Text]
Received February 24, 2003;
accepted after revision April 29, 2003.
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Abstract
Introduction