Endoscopic hypophysectomy
Contents
History:
1980's heralded the nasal endoscope. It soon became an important tool in the armamentorium of the otolaryngologist. It really took them to areas which were previously beyond their realms of imagination. Access to these areas soon became reality. The illumination and visualization provided by the nasal endoscope was simple unparalleled. Simultaneously CT scan study of para nasal sinuses also gained in popularity, enabling the surgeon to have an exact understanding of the anatomy of this crucial area. Soon the "neglected sinus" (adage for sphenoid sinus) became the most studied sinus. In fact it threw up an important gateway to access pituitary gland.
It was Jankowski etal in 1992 who performed successful endonasal endoscopy assisted resection of pituitary adenoma. In fact they reported successful removal in three patients. It soon became a sensation, and surgeons all over started following it.
Surgical anatomy:
A study of surgical anatomy of sphenoid sinus is a must for successful completion of this surgical procedure. Depending on the extent of pneumatization sphenoid sinus has been classified into three types i.e. conchal, presellar and sellar.
Conchal type:
In this type the area below the sella is a solid block of bone without an air cavity. This type is common in children under the age of 12 because pneumatization begins only after the age of 12.
Presellar type:
In this type the air cavity does not penetrate beyond the coronal plane defined by the anterior sellar wall.
Sellar type:
In this type the air cavity extends into the body of the sphenoid below the sella and may extend as far posteriorly as theclivus. This type is commonly seen in 85% of individuals.
The sphenoid ostium is located in the sphenoethmoidal recess. It can be commonly seen medial to the superior turbinate about 1.5 cms superior to the posterior choana. In fact it lies just a few millimeters below the cribriform plate.
The right and left sphenoidal sinus is separated by a intersinus septum. The position and attachement of this septum is highly variable.
Possible variations of intersinus septum are as follows:
1. A single midline intersinus septum extending on to the anterior wall of sella.
2. Multiple incomplete septae may be seen
3. Accessory septa may be present. These could be seen terminating on to the carotid canal or optic nerve.
Lateral wall of sphenoid sinus: is related to the cavernous sinus. This sinus is formed by splitting of the dura. It extends from the orbital apex to the posterior clinoid process. Cavernous sinus contains very delicate venous channels, cavernous part of internal carotid artery, 3rd, 4th and 6th cranial nerves. It also contains some amount of fatty tissue.
The prominence of internal carotid artery is the postero lateral aspect of the lateral wall of sphenoid sinus. This prominence can be well identified in pneumatized sphenoid bones. On the antero superior aspect of the lateral wall of sphenoid sinus is seen the bulge formed by the underlying optic nerve. These two prominences are separated by a small dimple known as the opticocarotid recess. The optic nerve and internal carotid artery is separated from the sphenoid sinus by a very thin piece of bone. Bone dehiscence is also common in this area.
In well pneumatized sphenoid sinus, the pterygoid canal and a segment of maxillary division of trigeminal nerve could be identified in the lateral recess of the sphenoid sinus.
The roof of the sphenoid (planum sphenoidale) anteriorly is continuous with the roof of ethmoidal sinus. At the junction of the roof and posterior wall of sphenoid the bone is thickened to form the tuberculum sella. Inferior to the tuberculum sella on the posterior wall is the sella turcica. It forms a bulge in the midline. The bone over the sella could be 0.5 - 1 mm thick. This may get thinner inferiorly. It is hence easy to breech the sella in this tinnest part. This area can be easily identified by a bluish tinge of the dura which is visible through the thin bony covering.
The main portion of the pituitary gland lies in the sella turcica and is connected to the brain by a stalk known as the infundibulum. In front of the infundibulum, the upper aspect of the gland is related directly to pia archnoid. The subarachnoid space hence extends below the diaphragm. This anatomy should be borne in mind before opening up the pituitary through the sphenoid sinus. The pituitary gland is related superiorly to the optic chiasma and below to intercavernous sinus. Inadvertant trauma to this sinus could cause troublesome bleeding, hence care should be taken to avoid this structure.
Indications for endoscopic hypophysectomy:
Secretory / Nonsecretory pituitary tumors. Non secretory tumors reach a large size before becoming symptomatic. These patients present with ocular symptoms due to pressure over optic chiasma, oculomotor nerve dysfunction due to involvement of cavernous sinus.
Most prolactin secreting pituitary adenomas respond well to bromocriptine, hence surgery can be withheld in these patients.
Tumors secreting growth / adrenocorticotrophic hormones are indications for early surgery to achieve endocrinological cure.
Patients with suspected aneuryms should undergo angiography.
Surgical technique:
Nasal cavities are decongested by use of nasal packs mixed with 4% xylocaine with 1 in 10,000 units adrenaline.
This surgery is performed under general anesthesia.
The patient is positioned supine with head elevated to 30 degrees. Patient's bladder is catheterised to monitor urinary output in the post op period.
Nasal endoscopic examination is performed using 0 degree and 30 degrees nasal endoscope. The sphenoid ostium is identified in the sphenoethmoidal recess on both sides. Surgery is usually started on the side where the sphenoid ostium is better visualized. The sphenoid ostium is widened inferiroly and medially till the floor of the sphenoid sinus is reached. The septal branch of sphenopalatine foramen if encountered is cauterized using bipolar cautery. The sphenoidotomy is extended to the opposite side by removing the rostrum of sphenoid. About 1 cm of the posterior part of vomer is removed with reverse cutting forceps.
After this step both ENT and Neurosurgeon work as a team. The neurosurgeon applies suction through left nostril to ensure that the operating field is clear. The bulges formed by the internal carotid artery and optic nerve are identified. Care must be taken while the intersinus septum is removed because it could be directly attached to the internal carotid artery, hence true cut instruments should be used.
A ball probe is used to access the thickness of the anterior wall of the sella, fracturing it at the thinnest portion. A kerrison punch is used to widen the opening. Dural bleeding is controlled using bipolar cautery. A cruciate incision is made. The vertical limb of the incision should not extend too superiorly to avoid subarachnoid space. The intercavernous sinus should be avoided inferiorly. Since most of these tumors are gelatinous and semisolid in nature, they can be easily sucked out by using a suction. Blunt ring curettes are used to remove the tumor completely.
The tumor removal is done in a systematic manner. It is usually started from the floor, then laterally and finally the supra sella component if any is attended to. The nasal cavity is packed with Merocel.
Post operative care:
The patient is kept in surgical ICU for 24 hours. Urinary output is monitored. Adequate doses of antibiotics are used parentally.
Complications:
1. CSF leak
2. Diabetes insipidus
3. Intrasellar hematoma
4. Death due to trauma to internal carotid artery
5. Blindness due to damage to optic nerve
CSF leak:
This is one of the commonest intraoperative complication. The usual cause is trauma to the diaphragma with instruments like curette, forceps etc. This area is very thin and highly susceptible to trauma. When csf leak is identified intraoperatively, the defect should be identified and repaired with intrasellar placement of abdominal fat and fibrin glue. Lumbar drainage is performed for 5 days. Minor weeping defects of dura can be expected to heal on its own.
Meningitis: This is an uncommon complication following surgery. Organisms involved include staph aureus, strep. pneumonia etc. Broad spectrum antibiotics should be used to manage these patients.
Diabetes insipidus: This complication may be transient / permanent. Commonly this condition is transient in nature. These patients should be managed with intranasal administration of desmopressin. Permanent diabetes insipidus may be caused by damage to pituitray stalk. during surgery.
Bleeding: Intraoperative bleeding may be caused due to inadequate nasal decongestion, excessive stripping of sphenoid mucosa, trauma to cavernous sinus, trauma to internal carotid artery. Persistent post op bleeding could be caused due to trauma to sphenopalatine artery and its branches.
Intrasellar hematoma: Transient / permanent loss of vision may be caused due to intrasellar hematoma / or due to direct damage to optic chiasma. In cases of intrasellar hematoma, CT scan should be done to clinch the diagnosis. Immediate evacuation of heamatoma should be done.
Contraindications:
1. Poor general condition of patient
2. Conchal type of sphenoid pneumatization
3. Prolactinomas
