Sphenoid bone

Keilbein, n. sphenoid bone cuneiform bone, keilen, v.t. wedge key. keilfdrmig, a. keilfthnlich. 

The pituitary gland lies deep within the cranial vault, connected to the brain by the infundibular stalk (a downward extension of the floor of the third ventricle) and protected by an indentation of the sphenoid bone called the sella turcica (see Fig. 50-1). The pituitary gland, a small, gray rounded structure, has two parts ... 

Transsphenoidal pituitary microsurgery Surgery through the nasal cavity to access the pituitary gland through the sphenoid bone. 

Among the symptoms seen in patients with type I NF are hyperpigmented skin lesions (cafe-au-lait spots), benign skin tumors (neurofibromas), dysplasia of the sphenoid bone, and benign tumors of the iris (hamartomas or Lisch nodules). 

The pituitary gland is situated in sella turcica or hypophyseal fossa of the sphenoid bone attached to the brain by a stalk which is continuous with the part of brain i.e. hypothalamus and there is a communication between the hypothalamus and the pituitary gland by means of nerve fibres and a complex of blood vessels. Pituitary gland consists of three parts - anterior lobe or adenohypophysis, posterior lobe or neurohypophysis and middle lobe or pars intermedia. 

The pituitary gland, also referred to as the hypophysis, is located at the base of the brain in a cavity of the sphenoid bone known as the sella turcica. The pituitary is separated from the brain by an extension of the dura mater known as the diaphragma sella. The pituitary is a very small gland, weighing between 0.4 and 1 g in adults. It is divided into two distinct regions, the anterior lobe, or adenohypophysis, and the posterior lobe, or the neurohypophysis (see Fig. 75-1). 

The lobes of the cerebrum surround a stalk of nervous tissue that connects the spinal cord with the upper neural centers of the cerebrum. These midline structures include the thalamus and the brainstem. The thalamus protrudes into the middle cranial fossa, above the level of the cUnoid processes of the sphenoid bone. It serves as a reciprocal gateway between the cerebral cortex and brainstem that conveys extensive sensorimotor and autonomic information. 

During its organogenesis, the hypophysis leaves tracks in an area between the pharynx and the hypophysis. Again, small epithelial nodules of hypophyseal cells are inserted within the mucosa. These residues of embryological structures may develop into hypophyseal tumors that are found in the roof of the nasopharynx, in the body of the sphenoid bone, in the capsule of the pituitary gland, within the pars intermedia, and around the infundibulum. Such tumors are most frequently found in the pituitary capsule and the infundibulum. 

Superiorly, below the frontal sinus and the anterior cranial fossa, the orbital roof is shaped by the frontal and sphenoid bones. 

Fig. 12.4a-f. Orbital metastasis of prostate cancer affects major wing of sphenoid bone and extraconal compartment of orbit, with bony spiculae extending into the intra-oibital soft tissue mass (arrows). Metastasis causes proptosis of left eyeball (axial MDCT images, a and b), compression of optic nerve in... 

Sphenoid The articulation of the occiput with the sphenoid was discussed under the sphenoid bone. 

The brain resides within the cranial cavity. The bony roof and sides of the cranial vault make up the calvaria, which is composed of frontal, temporal and parietal bones and a small portion of the occipital bone. The floor of the cranial vault is divided into three depressions or fossae the anterior fossa extends from the region superior to the orbits and nasal cavity caudaUy as far as the posterior margin of the lesser wing of the sphenoid the middle fossa occupies the region between the lesser wing of the sphenoid and the anterior border of the petrous portion of the temporal bone and the posterior fossa, is underlain by the remainder of the temporal bones and the occipital bone. 

Medially, the bony orbit is confined by the ethmoid, lacrimal, sphenoid, and maxillary bones. The most anterior part of the medial wall of the orbit includes the nasolacrimal fossa, with the aperture of the nasolacrimal duct. 

Laterally, the orbital wall includes parts of the zygomatic, sphenoid, and frontal bones and neighbors the temporalis fossa laterally and the middle cranial fossa posterolaterally. 

The free or inner concave border forms the tentorial notch, which surround the midbrain and is classically described as attaching to the anterior clinoid processes of the sphenoid. The attached or outer convex border is classically described as attaching to five areas the transverse ridge of the sulcus of the transverse sinus of the occiput, the posteroinferior angle of the parietal bone at the asterion, the mastoid portion of the temporal bone, the petrous ridge of the temporal bone, and the posterior clinoid process of the sphenoid. 

The bilaterally paired cavernous sinuses are found lateral to the sella turcica and extend from the sphenoidal fissure to the apex of the petrous portion of the temporal bone. Cranial nerves III, IV, VI, the ophthalmic division of V, and the internal carotid artery are all found in relation to the cavernous sinuses. The sinuses are fed by ophthalmic veins, and drain to the superior and inferior petrosal sinuses, the sigmoid sinus, and then to the internal jugular vein. Dysfunction at the tip of the petrous portion of the temporal can interfere with the outflow of the cavernous sinus into the narrow petrosals. 

The sphenoid articulates with 12 bones (Fig. 103-8). It is influential in the motion of the frontal and facial bones. It is important to note that the bones are not prime movers. They have mobility and the ability to change shape, and will... 

Occiput The sphenoid articulates with the basilar portion of the occiput (the spheno-basilar joint), a synchrondrosis that is cartilaginous until age 20 to 25 years, and then converts to cancellous bone. It exhibits flexibility, not articular mobility. 

Parietals A small articulation exists at the pterion between the posterosuperior surface of the greater wing of the anterior inferior angle of the parietal bone. It is a squamous suture, allowing gliding motion. The sphenoid overlaps the parietal bone. 

The frontal bone acts as paired bones do, rotating externally under the influence of the sphenoid. The axis of motion runs from the frontal eminence through the center of the orbital plate. The inferior lateral angles move laterally and anteriorly. The glabella recedes slightly under the influence of the falx. 

The nasal sinuses include four pairs of aerated cells in the bones of the skull, named after the four bones in which they are located frontal, sphenoid, ethmoid, and maxillary. These sinuses are lined with epithelium similar to that of the nasal passages. This epithelium contains goblet cells that secrete mucus, which is normally moderately thin and clear, and ciliated cells whose purpose is to move the secretions out of the sinuses into the nasal passages, assisted by gravity. 

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