Examination And Removal Of Structures At Base Of Skull

VENOUS SINUSES, GANGLIA, AND DURA The venous sinuses including the cavernous sinuses are opened with curved scissors after removal of the brain. The Gasserian ganglia can be removed at this time. The dura at the base of the skull should be thoroughly stripped. This procedure is essential for exposing fracture lines. Before the dura is stripped, chisel and hammer should be used with caution because they may create arti-factual fractures. Removal of the cavernous sinuses with their contents may be indicated, as in a case of aneurysm of the internal carotid artery, and in such a case, the method described next for the in situ removal of the pituitary gland can be used.

PITUITARY GLAND The margins of the diaphragma sellae should be incised before the posterior clinoid is knocked off with a small chisel. The tip of the chisel is placed at the crest of the dorsum sellae. The chisel can be directed either posteriorly (downward) over and nearly parallel to the midline anterior fossa or nearly perpendicular to it. If the chisel is placed perpendicularly, the pituitary remains visible during the procedure but a tap is needed over the broad side of the chisel near the tip, instead of a tap on the end of it. The diaphragma must be freed first or the tension on it may result in squeezing of the tissue in the pituitary fossa. A pair of forceps is applied to the edge of the diaphragma and the pituitary is dissected out, with a sharp blade, away from the base of the fossa. The pituitary gland may be removed with its bony encasement, for example, in a case of pituitary adenoma. For this, saw cuts are made along the lines indicated in Fig. 6-9 and the entire block is lifted off the base of the skull. With normal pituitary glands, removal from the fossa becomes more difficult after fixation, because the gland enlarges and the dura adheres firmer to the sella. For histologic examination, it is best to cut the pituitary gland after fixation.

A method to remove the hypothalamus and the pituitary gland and its bony encasement in continuity is available also (13). Should this be indicated, most the brain is resected and only the hypothalamus and pituitary gland are left in situ. The block is lifted with the cavernous sinuses and posterior lining of the sella attached. For better preservation of the cerebral tissue, one can remove the frontal lobes, along the coronal plane at the level of the lamina terminalis, and free the pituitary from the pituitary fossa by sharp dissection and, if necessary, with use of a small rongeur to chip some of the bones. The remainder of the brain is removed as usual.

PARANASAL SINUSES AND NASOPHARYNX Various paranasal sinuses can be entered in tracranially for inspection or removal of specimens for histologic observation. The ethmoid sinuses can be approached by breaking the cribriform

plate with a chisel and mallet. Continued chiseling leads into the maxillary sinuses. The frontal sinuses are entered by chiseling away their posterior walls close to the midline. The sphenoidal sinuses can be inspected after the anterior wall and the floor of the pituitary fossa have been exposed. If the block of bone containing the pituitary fossa is removed (Fig. 6-9) with an oscillating saw, the sphenoidal sinuses are exposed even better. The nasopharynx and the throat can be entered by extending this dissection. For an excellent review of nasopharyngeal dissection methods, see ref. (14). More recently, en bloc resection of all ENT-relevant organs without disfiguring the body has been described (15).

EAR Even when there is no indication for removing the auditory and vestibular apparatus in one piece, it is still a good practice to look into the middle and inner ear, particularly in the presence of an inflammatory process within the cranial cavity. This can be done simply by the use of a large rongeur over the posterolateral portion of the petrous ridge. A primary focus of infection may be found within the ear structures. When total removal of the ears is indicated, we apply the method described in the pamphlet from the Temporal Bone Bank (16). The use of an oscillating saw facilitates the procedure.

The cut is made along the lines indicated in Fig. 6-10A. The block of bone thus sectioned is lifted with a bone-holding forceps, and the connective tissue bands anchoring the block are cut with curved scissors. When the temporal bone is freed, chisel and hammer should be used with caution. The internal carotid artery stump should be ligated or, simpler still, plugged with clay to help the embalmer. Alternatively, a bone-plug cutter attached to the vibrating saw (Fig. 6-10B) can be used. The Temporal Bone Bank recommends the use of 20% formalin solution, approx 400 mL, for fixation in a refrigerator for 1 d and fresh 10% formalin solution daily for 2 additional days. Refrigerated specimens can be saved indefinitely. Following a short decalcification, the specimen can be sliced and processed for light microscopy (17).

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

Get My Free Ebook


Post a comment