Microsurgical anatomy of the sellar region

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✓ Fifty adult sellae and surrounding structures were examined under magnification with special attention given to anatomical variants important to the transfrontal and transsphenoidal surgical approaches. The discovered variants considered disadvantageous to the transsphenoidal approach were as follows: 1) large anterior intercavernous sinuses extending anterior to the gland just posterior to the anterior sellar wall in 10%; 2) a thin diaphragm in 62%, or a diaphragm with a large opening in 56%; 3) carotid arteries exposed in the sphenoid sinus with no bone over them in 4%; 4) carotid arteries that approach within 4 mm of midline within the sella in 10%; 5) optic canals with bone defects exposing the optic nerves in the sphenoid sinus in 4%; 6) a thick sellar floor in 18%; 7) sphenoid sinuses with no major septum in 28% or a sinus with the major septum well off midline in 47%; and 8) a presellar type of sphenoid sinus with no obvious bulge of the sellar floor into the sphenoid sinus in 20%.

Variants considered disadvantageous to the transfrontal approach were found as follows: 1) a prefixed chiasm in 10% and a normal chiasm with 2 mm or less between the chiasm and tuberculum sellae in 14%; 2) an acute angle between the optic nerves as they entered the chiasm in 25%; 3) a prominent tuberculum sella protruding above a line connecting the optic nerves as they entered the optic canals in 44%; and 4) carotid arteries approaching within 4 mm of midline within or above the sella turcica in 12%.

Article Information

Address reprint requests to: Albert L. Rhoton, Jr., M.D., Division of Neurological Surgery, University of Florida Health Center, Gainesville, Florida.

© AANS, except where prohibited by US copyright law.

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Figures

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    Superior view of sellar region. Upper: Prefixed chiasm. Center: Normal chiasm. The ophthalmic artery protrudes medial to the right optic nerve. The anterior cerebral arteries pass dorsal to the chiasm. The left recurrent artery arises from the A-1 segment of the left anterior cerebral artery. The pituitary stalk lies between the optic nerves. Lower: Postfixed chiasm. Diaphragma sellae and pituitary gland removed. The third nerve (CN III) lies ventral to the carotid arteries.

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    Superior view of sellar region, showing carotid arteries lateral to optic nerves, anterior cerebral arteries stretched across superior surface of the optic chiasm, and right optic nerve shorter than the left.

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    Anterior view of sphenoid sinus. Anterior wall of sella bulges into the posterior part of the sinus. The optic canals bulge into posterosuperior part of the sinus. The major septum is located off the midline and separates the sinus into asymmetrical cavities.

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    Superior view of sellar region. Optic chiasm is reflected forward, and a congenitally absent diaphragm exposes the superior surface of pituitary gland. Arachnoid covers superior surface of gland, and the third cranial nerve is posterior to carotid arteries.

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    Superior view of sellar region. Ophthalmic arteries arise from superior aspect of carotid artery and course laterally beneath the optic nerves to the optic foramen. The dura over the cavernous and anterior intercavernous sinuses has been removed to show the venous connection across the midline.

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    Midline sagittal section of sellar region showing anterior and posterior intercavernous and basilar sinuses. The basilar sinus connecting the posterior aspect of both cavernous sinuses is the largest connection across the midline. An intermediate lobe cyst separwtes the anterior and posterior lobe of the pituitary gland. Anterior sellar wall bulging into sphenoid sinus is 1 mm thick.

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    Midline sagittal section of sellar region showing optic nerve and chiasm, third cranial nerve (CN III), inferior part of hypothalamus, and pituitary stalk and gland. The anterior and inferior intercavernous sinuses are small. The basilar sinus, dorsal to the clivus, joining the posterior aspect of the two cavernous sinuses is the largest connection across the midline. Anterior sellar wall bulging into the sphenoid sinus is very thin.

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    Schematic drawing of six sagittal sections of sellar region showing variation in intercavernous venous connections (blue) within dura (red). Variations shown include combinations of anterior, posterior, and inferior intercavernous connections and the frequent presence of a basilar sinus posterior to the dorsum. Either the anterior (lower center) or posterior (lower left) intercavernous connection or both (top center) may be absent. The anterior intercavernous sinus may extend along the whole anterior margin of the gland (lower left). The basilar sinus is frequently absent (lower right).

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    Superior view of sellar region showing optic nerves, carotid arteries, third and sixth cranial nerves (CN III and VI), and pituitary stalk. The basilar sinus connects the posterior portion of the two cavernous sinuses. The dura over the posterior aspect of the left cavernous sinus and the left half of the basilar sinus was removed. The course of the basilar, inferior petrosal and superior petrosal sinus within the dura is shown by the dotted lines.

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    Inferior surface of sella as seen through upper half of the sphenoid sinus. Optic canals bulge into superolateral and the carotid arteries bulge into the inferolateral parts of the sinus. The major septum deviates off the midline as it approaches the sellar floor. The sellar floor to the right of the septum is so thin that light transmits through it.

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    Schematic representation of septae in sphenoid sinus. Broken line on central diagram shows plane of section of each specimen from which drawings were taken and the large arrow shows the direction of view of the specimens. Planum is above, dorsum and clivus below, and sella in an intermediate position on each diagram. Carotid arteries represented as double circles in each diagram. Heavy dark line on each drawing shows location of septae in sphenoid sinus. A wide variety of septae separate the sinus in cavities which vary in size and shape, seldom being symmetrical from side to side.

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    Inferior view of sella through sphenoid sinus. Sinus composed of a single large cavity not divided by a septum. Right carotid artery separated from sinus only by sinus mucosa. Left carotid artery covered by bone less than 1 mm thick.

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    Superior view of sellar region showing optic nerves, carotid arteries, and third cranial nerves. Carotid arteries bulged into the pituitary fossa.

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    Superior view of sellar region. Long, tortuous anterior cerebral arteries above the optic chiasm. The A-l segment of the right anterior cerebral artery loops in a complete circle between its origin from the carotid artery and its junction with its mate from the opposite side at the anterior communicating artery. Tortuous left anterior cerebral artery rests against the tuberculum sellae covering the prechiasmatic space.

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