Congenital Abnormalities of the Sellar and Parasellar Regions

Congenital Abnormalities of the Sellar and Parasellar Regions Division of Neuroradiology Department of Radiology University of North Carolina at Chapel Hill

Purpose • To present the imaging appearances of congenital diseases arising in the sellar and suprasellar regions • To demonstrate how the embryological correlations of the pituitary gland with the adjacent structures facilitate the correct interpretation of sellar and parasellar congenital abnormalities

Embryology The pituitary gland consists of two embryological and functionally distinct divisions: – Adenohypophysis (pars anterior, pars intermedia and pars tuberalis) – Neurohypophysis (median eminence, infundibular stem and pars posterior)

Embryology • Development of the pituitary gland begins in the 4 th week of life with inductive signals from the diencephalon initiating the formation of Rathke's pouch • Rathke’s pouch has been considered as a diverticulum of the epithelium lining of the stomodeum but recent evidence indicates it is a derivative of neural ectoderm from the anterior neural ridge

Embryology • By the 8 th week of life, the primitive adenohypophysis separates from the oral cavity and primitive pituitary cells undergo rapid proliferation with differentiation into specialized hormone lines • Adenohypophysis consists of: pars anterior or distalis, pars intermedia (rudimentary in humans) and pars tuberalis (along the stalk)

Embryology • Neurohypophysis originates from a neuroectodermal evagination of tissue in the diencephalic floor which grows to the stomodeal roof. An extension of the 3 rd ventricle (the infundibular recess), persists in the neuroectodermal diverticulum of the forebrain • Neurohypophysis is divided into median eminence, infundibular stem and pars posterior

Embryology Figure 1 A. 6 -week embryo shows the dual origin of the gland from Rathke's pouch and from diencephalic floor (infundibulum) (used with permission). Sadler, T. , Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect, 2000; 108: 555

Embryology Figure 1 B. Pituitary at 11 weeks of life. The gland is formed and a cleft persists between pars intermedia and pars anterior. The craniopharyngeal canal closes and occasionally the adenohypophysis remains in the nasopharynx (used with permission). Sadler, T. , Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect, 2000; 108: 555

Embryology Figure 1 C. Pituitary gland at 16 weeks of life. The gland acquires an ‘adult’ configuration and the craniopharyngeal canal closes (used with permission). Sadler, T. , Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect, 2000; 108: 555

Embryology • Regulation of pituitary embryogenesis involves a cascade of genes expressed during the 4 th week of life in the diencephalon initiating formation of Rathke‘s pouch and later a combined expression of multiple genes throughout the stomodeal epithelium required for morphogenesis of the pouch and proliferation and differentiation of hormone specific cells

Newborn Pituitary Gland • In neonates the pars anterior and pars posterior are both uniformly bright on the T 1 images • At birth the pituitary gland may also be globular in shape • This appearance likely reflects the hormonal surges that occur perinatally • The signal intensity and size of the pituitary gland becomes similar to older children’s appearance by two months of age

Newborn Pituitary Gland Figure 2. Sagittal non-contrast T 1 image shows pituitary gland at 5 days of age. Until 2 months of age, the pituitary gland is uniformly bright

Abnormal Separation of Ectoderm and Neuroectoderm

Transsphenoidal Encephalocele • It is an “occult” encephalocele characterized by a bone defect in ethmoid or sphenoid bone • Usually diagnosed later than other forms of encephaloceles • Hypothalamus, pituitary gland, 3 rd ventricle, optic nerves and chiasm may be located in the encephalocele sac • Typical clinical presentation: nasal obstruction, difficulty feeding and failure to thrive

Transsphenoidal Encephalocele A B Figure 3. Sagittal post-Gd T 1 (A) and T 2 (B) images show herniation of a CSFfilled sac (white arrows) through a bone defect in the body of the sphenoid. The neurohypophysis (black arrow) is also noted. Agenesis of the corpus callosum (C/o of Dr. A. Rossi).

Congenital Abnormalities Development of the Hypothalamo-Pituitary Axis

Hypoplastic Pituitary Gland • Pituitary hypoplasia is a congenital disorder involving the adenohypophysis, neurohypophysis and often the stalk • Patients with pituitary hypoplasia survive with hormonal replacement but pituitary aplasia is incompatible with life • Pituitary dwarfism due to deficiency of growth hormone is a common clinical presentation

Hypoplastic Pituitary Gland A B Figure 4. Coronal (A) and sagittal (B) T 1 images show small pituitary gland stalk.

Pituitary and Hypothalamic Hypoplasia Figure 5. Sagittal T 1 image shows hypoplastic pituitary gland (black arrow), hypothalamus and optic chiasm (white arrow).

Ectopic Neurohypophysis • It is characterized by a “bright spot” along median eminence of hypothalamus or along stalk which may be tiny or absent • Adenohypophysis and sella may be small • Frequently associated with growth hormone deficiency (pituitary dwarfism) • Associated adenohypophysis dysfunction may be related to absent infundibulum • Associated midline CNS abnormalities: (septooptic dysplasia, lobar holoprosencephaly, olfactory bulb anomalies)

Ectopic Neurohypophysis A B Figure 6. Pre- (A) and post-Gd (B) sagittal T 1 images show “bright spot” in tuber cinereum of the hypothalamus

Ectopic Neurohypophysis with Thin Stalk Figure 7. Sagittal T 1 image shows ectopic neurohypophysis (black arrow) in tuber cinereum and hypoplastic pituitary stalk (white arrow).

Duplicated Pituitary Gland • Rare congenital disorder due to duplication of primitive stomodeal structures • Two sellae, lateral stalks and glands are present • Mammillary bodies are fused with tuber cinereum, thickening of 3 rd ventricle floor (hamartoma? ) • Basilar artery shows lack of longitudinal fusion • Anterior 3 rd ventricle may be duplicated • Possible association with CN I and II hypoplasia • Pituitary-related symptoms are rare • Associations: craniofacial clefting, oral midline tumors, dysgenesis of corpus callosum, Dandy-Walker spectrum

Duplicated Pituitary Gland A B Figure 8. Post–Gd coronal (A) and axial (B) T 1 images show two stalks (arrows), pituitary glands and sellae.

Tuber Cinereum Hamartoma • It is a congenital malformation characterized by heterotopia of gray matter in the region of the mammillary bodies or tuber cinereum • Round non-enhancing pedunculated or sessile mass, contiguous with tuber cinereum; isointense to gray matter on T 1 and slightly T 2 bright • Isosexual precocious puberty due to LHRH and/or gelastic seizures • Common associations: congenital facial/cerebral midline abnormalities, visceral anomalies, digital malformations • Differential diagnosis: hypothalamic astrocytoma, hystiocytosis, germ cell tumor

Tuber Cinereum Hamartoma A B C Figure 9. Post–Gd T 1 (A), T 2 (B) sagittal, and post-Gd T 1 axial (C) images. A mass is seen between the infundibulum and mammillary bodies, hyperintense to gray matter on T 2. The mass appears similar to the brain parenchyma on T 1 and shows no enhancement (courtesy of Dr. A. Osborn).

Tuber Cinereum Hamartoma A B Figure 10. Post–Gd sagittal T 1 (A) and T 2 (B) images show a large tuber cinereum hamartoma that is T 1 isointense and T 2 bright (courtesy of Dr. A. Osborn).

Optic Infundibular Hypoplasia • Disorder of midline prosencephalic development (6 th weeks of life) • Overlaps with septo-optic dysplasia but septum pellucidum is present • Optic chiasm/optic nerves are hypoplastic • Pituitary hypoplasia, thin stalk, ectopic neurohypophysis may be present

Optic Infundibular Hypoplasia A B C Figure 11. Sagittal T 1 (A), coronal T 2 (B) and T 1 (C). A: Hypoplastic pituitary gland, stalk, optic chiasm and hypothalamus. B: Hypoplastic optic nerves. C: Ectopic neurohypophysis (arrow).

Congenital Disorders Development of the Adenohypophysis

Persistent Craniopharyngeal Canal A B Figure 12. Sagittal T 1 (A) and coronal T 1 (B) images. The craniopharyngeal canal is patent. The adenohypophysis is within the canal (arrow) and extends into the nasopharynx (arrowhead) (C/o of Dr. M. Michel)

Persistent Craniopharyngeal Canal A B Figure 13. Sagittal T 1 MR (A) and axial CT (B) images. A: The adenohypophysis (arrow) is in a persistent craniopharyngeal canal. B: Shows persistence of a craniopharingeal canal (arrowhead) (C/o Dr. K. Marsot. Dupuch).

Rathke’s Cleft Cyst • Non-neoplastic cyst arising from remnants of squamous epithelium of Rathke’s cleft • Non-enhancing non-calcified intra or suprasellar cyst • Variable cyst content: mucous (T 1 bright) serous (T 1 dark) and possible blood products (T 2 dark)

Rathke’s Cleft Cyst A B Figure 14. Pre- (A) and post-Gd (B) T 1 weighted images show an intrasellar mass (black arrow) that is bright compared to normal pituitary gland (white arrow). Location (middle 1/3 of gland) and signal intensity strongly suggest a Rathke’s cleft cyst

Rathke’s Cleft Cyst Figure 15. Axial T 2 image shows intrasellar mass with fluid level (arrow) a typical feature of Rathke’s cleft cyst; the differential diagnosis includes a hemorrhagic pituitary adenoma.

Craniopharyngioma • Benign dysontogenetic epithelial tumor arising from cell remnants of Rathke’s pouch • Complex mass, with inhomogeneous enhancement of solid components • Calcifications: very common • T 1 signal varies with cyst contents • Bimodal age distribution (5 -15 y; > 50)

Craniopharyngioma A B Figure 16. Sagittal post-Gd T 1 (A) and coronal T 2 (B) images show an enhancing suprasellar mass (arrows) with complex appearance.

Craniopharyngioma A B Figure 17. Coronal (A) and sagittal (B) post-Gd T 1 images show a suprasellar cystic mass (white arrows). A solid enhancing nodule is noted (black arrow) and the rim also enhances (small white arrows).

Pars Intermedia Cyst • These cysts arise in the pars intermedia of the adenohypophysis which is rudimentary in humans • They are usually less than 3 mm in diameter • They are located between the pars anterior and pars posterior

Pars Intermedia Cyst A C B Figure 18. Sagittal pre- (A) and post-Gd (B) T 1 images and (C) axial T 2 image show nonenhancing cyst (arrows) between the pars anterior and pars posterior.

Miscellaneous

Dermoid • Intracranial dermoids are ectodermal inclusion cysts that originate from midline inclusion of surface ectoderm during the 3 rd-5 th weeks of life at the time of closure of the neural tube • Common intracranial locations: frontonasal, sellar and parasellar regions, posterior fossa and ventricles • Dermoids are T 1 bright due to presence of lipids and cholesterols and may rupture with spreading of fat droplets along the CSF containing spaces resulting in aseptic meningitis

Dermoid Figure 19. Sagittal T 1 image shows a well-defined bright midline suprasellar mass (arrows).

Teratoma • Teratomas are composed of tissues from the three embryonic germ layers • The majority of teratomas are supratentorial in the region of the optic chiasm and in the pineal gland • They are midline tumors containing fat, soft tissue and calcifications • Classified as mature, immature and malignant • Occasionally they present in newborns as holocranial tumors

Teratoma A B Figure 20. Sagittal non-contrast T 1 (A) and axial fat-suppressed T 2 (B) images show a heterogeneous suprasellar mass (arrows) due to presence of calcifications and fat.

References Barkovich, A. , Pediatric Neuroimaging. 3 rd edition ed. 2000, New York: Raven Press. Chen, C. , D. David, and A. Hanieh, Morning glory syndrome and basal encephalocele. Childs Nerv Syst, 2004(20): p. 87 -90. Chong, B. and T. Newton, Hypothalamic and pituitary pathology. The Radiology Clinics of North America, 1993. 31(5): p. 1147 -1183. Dietrich, R. , et al. , Normal MR appearance of the pituitary gland in the first two years of life. AJNR, 1995. 16: p. 1413 -1419. Gray, H. , Gray’s Anatomy. 37 th edition ed. 1989, New York, Churchill Livingstone. Osborn, A. , Diagnostic Imaging. Brain. 2004, Salt Lake City: Amirsys. Sadler, T. , Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect. , 2000. 108: p. 555 -561. Shroff, M. , et al. , Basilar artery duplication associated with pituitary duplication: a new finding. AJNR, 2003(24): p. 956 -961.