Abnormalities of the Sella Turcica

► [Variation in shape and/or size of the sella turcica]

The sella turcica is a cup-shaped depression in the central basisphenoid bone, which contains the pituitary gland and inferior part of the infundibular stalk. The sellar floor is continuous anteriorly with the tuberculum sellae and posteriorly with the dor-sum sellae. The sella turcica is bordered superiorly by a dural mirror image, the diaphragma sellae, which separates the sella turcica from the suprasellar subarachnoid space. This space is surrounded by the cir-

Pic Shaped Sella
Fig. 1.32. Hurler syndrome in a 2-year-old boy. Note the typical J-shaped sella turcica. Also observe macrocrania with frontal bossing, and thickened orbital roofs (arrows) and calvaria

cle of Willis and contains the optic nerves and chiasm and the upper part of the infundibular stalk. The hypothalamus and anterior third ventricular recess lie just above the infundibular stalk. The sella turcica is bordered laterally by the thin medial dural reflection of the cavernous sinus, a multiseptate venous channel that contains the internal carotid artery, cranial nerves III, IV, and VI, and the ophthalmic (V1) and maxillary (V2) divisions of the trigeminal nerve. Below the sella the sphenoid sinus is located (Osborn and Rauschning 1994). A number of lesions can affect this anatomically complex region, but a comprehensive description of all of them goes beyond the scope of this book. In this section, the principal conditions causing destruction, enlargement, or diminished volume of the sella are briefly outlined.

In the medical literature there are several radiographic descriptions of 'typical' configurations of the sella turcica, including elongated or stretched sella (elongated tuberculum sellae, with normal dorsum sellae), omega-shaped sella (undulating chiasmatic sulcus),balloon-like sella (homogeneously expanded sella), and J-shaped sella (flattened tuberculum sellae) (Swischuk and John 1995). Although J-shaped sella turcica has been associated with mucopolysaccha-ridoses (Fig. 1.32), achondroplasia, chromosome 18 trisomy syndrome, and omega-shaped sella can occur with tumors involving the optic chiasm; neither configuration is specific, as both also occur as developmental variants in the normal population. Additional variants include bridging of the sella turcica owing to ossification of the interclinoid ligament

Sella Turcica Anomalies

Fig. 1.33 a, b. Bridged sella turcica. a In a 12-year-old girl. Note ossification of the interclinoid ligament, or diaphragma sellae, and overall diminution of the pituitary fossa volume. There were no endocrinological abnormalities in this young woman. b In an adult male. Magnification of the sellar region showing complete ossification of the diaphragma sellae to better advantage

Fig. 1.33 a, b. Bridged sella turcica. a In a 12-year-old girl. Note ossification of the interclinoid ligament, or diaphragma sellae, and overall diminution of the pituitary fossa volume. There were no endocrinological abnormalities in this young woman. b In an adult male. Magnification of the sellar region showing complete ossification of the diaphragma sellae to better advantage

(Fig. 1.33a,b) (pseudobridging, on the other hand, is a projectional artifact attributable to overlapping of the anterior and posterior clinoid processes) and the presence of a medial clinoid process located between the anterior clinoid processes.

Erosion and/or Destruction of the Sella Turcica. Erosion and destruction of the sella turcica can occur with any of several intracranial tumors, including pituitary adenoma, craniopharyngioma, meningioma, primary or secondary neoplasms involving the sphenoid bone, chordoma, mucocele of the sphenoid sinus, and nasopharyngeal carcinoma. Craniopharyngioma, an embryonal tumor arising from squamous epithelial remnants of Rathke's pouch, often extends into the pituitary fossa, causing sellar enlargement and destruction of variable degree. The typical craniopharyngioma is a lobulated, well-delineated cystic mass with a mural nodule, which often (90%) contains gritty, nodular, or rim calcifications (Zimmerman 1990). Craniopharyngiomas account for 3-5% of all primary intracranial brain tumors and are the most common nonglial brain tumor in children. More than 50% of craniopharyngiomas occur in children,with a peak between 8 and 12 years of age. A second peak occurs in middle-aged adults (Hoffman et al. 1992). Rathke's cleft cysts are dysplastic lesions that originate from remnants of Rathke's pouch, an embryologic precursor of the anterior lobe, pars intermedia, and pars tuberalis of the pituitary gland (Crenshaw and Chew 1992). These cysts are smoothly marginated cavities of varying size (from only a few millimeters to 1-2 cm), lined with well-differentiated, ciliated columnar epithelium and with a serous or mucoid content that is usually rich in proteins (Kucharczyk et al. 1987; Hayashi et al. 1999). Occasionally, epithelial stratification occurs in response to inflammation, producing an enlarging mass that may extend into the adjacent adeno- or neurohy-pophysis,resulting in pituitary dysfunction (Hama et al. 2002). Small asymptomatic cysts are seen as an incidental finding in 2-26% of routine autopsies (Voelker et al. 1991; Teramoto et al. 1994). Rathke's cleft cysts do occasionally become large enough to cause symptoms, which can include visual disturbances, headaches, and signs of hypothalamic-pitu-itary dysfunction. There can be hemorrhage and cholesterol deposition within large cysts. Surgical removal of the cyst is usually recommended in symptomatic cases. Craniopharyngioma, pars intermedia colloid cysts, and Rathke's cleft cysts are regarded as different expressions of the same developmental anomaly (Oka et al. 1997).

Chordoma of the clivus is frequently associated with erosion of the dorsum sellae and the sellar floor. Gliomas of the optic nerve and hypothalamus may erode the clinoid processes. Furthermore, osteolysis of the dorsum sellae and clinoids sometimes occur in childhood leukemia and Langerhans cell histiocyto-

sis, whereas transitory demineralization, often reversed by appropriate therapy, can be seen in infants with rickets. Chronically increased intracranial pressure may lead within months to erosion of the dor-sum sellae and clinoid processes, followed by enlargement of the pituitary fossa if the primary cause is not removed. Transsphenoidal encephaloceles (see section "Congenital Ossification Defects") are associated with a bone defect in the sellar floor, usually without enlargement of the pituitary fossa.

Enlarged Sella Turcica. Enlargement of the sella turci-ca can be due to a slow-growing intrasellar mass (pituitary macroadenoma, craniopharyngioma, menin-gioma, arterial aneurysm or ectatic internal carotid artery, carotid-cavernous fistula) or an extension of the meningeal space into the pituitary fossa through the diaphragm sellae (arachnoid cyst, 'empty' sella, chronic communicating hydrocephalus, pseudotumor cerebri, polycystic intrasellar dilatation of the infundibular recess, Rathke's cleft cysts), or it can be a response to pituitary hyperplasia (bilateral adrenal ablation or Nelson syndrome, long-term hypothyroidism, hypogonadism) (Gibby et al. 1993; Fukushi-ma et al. 1994; Oka et al. 1994; Yuh et al. 2000). It can also occur as one feature of the Turner syndrome (OMIM 163950) (in association with thinning of the posterior clinoids and dorsum sellae, double floor, and calcification of the petroclinoid ligaments) or Saethre-Chotzen syndrome (OMIM 101400). Macro-adenomas usually cause widening of the sella turcica, but with preservation of the sellar contours. Clinical symptoms relate to the endocrine dysfunction and/or direct compression by the mass of such structures as the optic chiasm, cranial nerves III through VI, and carotid artery. 'Empty'sella is the designation for intrasellar herniation of the meningeal space, which results in a neuroanatomical picture in which the pituitary gland appears to be thinned and flattened against the sellar floor, the bulk of the sellar space being filled with CSF (Kaufman et al. 1970; Sage et al. 1980). The infundibular stalk follows its normal course and inserts in the midline of the pituitary gland. Since the pituitary gland is present and well functioning the designation is a misnomer. This type of empty sella is a very common finding in the elderly and is linked with the normal decrease in size of the pituitary gland that occurs with aging (Do-raiswamy et al. 1992). In rare cases the pituitary gland is truly absent, for example in cases of congenital agenesis or acquired destruction (Sheehan syndrome, meaning pituitary gland apoplexy of the postpartum period due to sudden incompetence of

Steinert Dystrophy
Fig. 1.34. Myotonic dystrophy (Steinert syndrome) in a 16-year-old male youth. Observe markedly small sella turcica, calvarial hyperostosis, and enlarged paranasal sinuses

the vascular supply to the hyperplastic pituitary gland while it is actively engaged in prolactin secretion; necrotic pituitary adenoma; surgical excision; irradiation therapy; syphilitic arachnoiditis; sar-coidosis). Another feature of these cases is that the subarachnoid space extends into the sella, producing a neuroanatomical and clinical picture for which the term 'empty' seems appropriate. Familial cases of empty sella are rare and are often associated with pituitary dysfunction (Merle et al. 1979). One such form, referred to as 'primary empty sella turcica with generalized dysplasia' (OMIM 130720), is discussed in the section "Wormian Bones."

Small, Shallow Sella Turcica. A small sella turcica sometimes occurs as a variant in otherwise normal individuals and can also be one feature of certain syndromes (Cockayne syndrome, Prader-Willi syndrome, nevoid basal cell carcinoma syndrome, Down syndrome, Hallermann-Streiff syndrome, myotonic dystrophy) (Fig. 1.34) or occur in association with pituitary gland aplasia/atrophy or as a result of decreased intracranial pressure (severe brain atrophy, shunted hydrocephalus, microcephaly). The disorders that cause selective or generalized deficiency of pituitary hormones are reviewed in Chapter 9. In disorders with macrocephaly, such as Sotos syndrome (OMIM 117550), the sella turcica appears small relative to the large head.

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Responses

  • renee
    What bone does the sella turcica occur on?
    8 years ago
  • emma
    What is abnormal sella turcica syndrome?
    3 years ago
  • RIIA
    How to see abnormalities of sella turcica?
    3 years ago
  • TECLA
    What are the cause of widening of sella turcica?
    3 years ago
  • tesfalem russom
    What is a j shaped sella in the skull?
    5 months ago
  • bonnie
    What is enlarged sella turcica?
    14 days ago

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