transsphenoidal hypophysectomy (by drdhiru456)
TRANSCRIPT
TRANSSPHENOIDAL HYPOPHYSECTOMY
-DR DHIRENDRA V. PATILM.S. (ENT)
J.N.M.C., Aligarh Muslim University.
INTRODUCTION
Pituitary tumors are commonly benign pituitary adenomas and only rarely are pituitary carcinomas or posterior pituitary neoplasias.
Pituitary adenomas present most commonly in the third and fourth decades.
Their clinical presentation depends whether the tumor is secreting (less common) or nonsecreting (more common).
Secreting adenomas present with the endocrine manifestations of the hormone secreted.
The most common is a prolactin-secreting tumor.
CLASSIFICATION OF PITUITARY TUMOURS
Histological classification –
Three types of anterior pituitary cells are traditionally described:
1. Chromophobe cells, which contain no granules,
2. Basophil and
3. Eosinophil cells.
Functional classification :
a) Functioning Adenomas -
-prolactinoma;
-GH-secreting adenomas: acromegaly;
-ACTH-secreting adenomas: Cushing’s disease and Nelson’s syndrome;
-TSH-secreting adenoma (TSHoma);
-gonadotrophinoma;
b) Non-functioning adenoma.
Size classification
Practical classification for pituitary adenomas.
Hardy described this in 1969 and it is still a useful classification in clinical practice.
1. Microadenomas are intrasellar lesions of up to 10mm in diameter.
These tumours will only present because they are functioning or because they are an incidental finding on a scan performed for other reasons (incidentalomas).
2. Macroadenomas are tumours of greater than 10mm in diameter.
They may or may not be functioning, and depending on their size and direction of spread they may cause symptoms
3. Mesoadenomas is the term used by some other authors for those tumours of intermediate size (10 mm) in diameter.
The smaller and more clearly defined the abnormality, the better the chance of removing it and preserving normal pituitary function.
CLINICAL FEATURES OF PITUITARY TUMOURS
1. Endocrine effects –
Mainly due to the effect of the excess of the hormone in question.
2. Space-occupying effects –
Superior expansion
Lateral extension
Inferior extension
Indications for hypophysectomy
Surgery can be carried out on the pituitary gland for diagnostic or therapeutic purposes.
Diagnostic: To obtain tissue for histology when a lesion has been identified which cannot be classified by biochemistry and imaging, or if histological confirmation is required for a lesion that is not treatable by surgery.
Therapeutic:
To treat an identified condition, such as a pituitary adenoma or other amenable pathology.
Contraindications for surgery
General contraindications include the following.
1. Uncontrolled disease caused by the adenoma. An example would be poorly controlled Cushing’s disease.
2. Poor general health. Once again the risk of anaesthetic and surgery should be minimized.
3. Increased risk of haemorrhage.
Local contraindications include the following:
1. Abnormal anatomy ,
2. Sinusitis, nasal vestibulitis or other significant nasal infections are a contraindication because of the risk of meningitis.
Patient information and consent
A detailed individual explanation is always necessary for all patients, which should include:
1. A careful explanation of the treatment options,
2. the serious nature of the condition and the surgery,
3. the way in which the surgery is carried out,
4. the nasal pack,
5. the importance of medication in the postoperative period,
6. The range of outcomes following surgery.
7. The likelihood of complications, their nature.
Preoperative investigations
For good surgical outcomes, the patient should be as fit as possible preoperatively.
ROUTINE LABORATORY INVESTIGATIONS :
A full blood count and biochemical profile are important as diseases of the pituitary have widespread effects.
PREOPERATIVE IMAGING :
MR scan is now the most useful imaging technique.
T1, without and with contrast, and T2 images are both valuable.
Coronal CT scanning of the sinuses and pituitary fossa provides the best bone detail, and so if there is a need for this detail (e.g. erosion of the clivus) this form of imaging should be used. [email protected]
MR angiography or conventional angiography may be used if there is any suggestion of a vascular lesion.
VISUAL FIELD ASSESSMENT :
Full records of the visual fields are required in the following circumstances:
1. if a patient with a pituitary tumourcomplains of any visual disturbance;
2. in the presence of a macroadenoma with tumour abutting on the optic nerves or chiasm.
Typical visual field abnormality is a bitemporalsuperior quadrantanopia or hemianopia.
Preparation for surgery
NASAL PREPARATION :
Use of vasoconstrictors in the nose is essential to reduce bleeding from the nasal mucosa and improve access.
Should include both,
1. The application of topical vasoconstriction (e.g. xylomatazoline 0.1 percent spray) to the nasal mucosa of both nostrils and
2. Injection of local anaesthetic agent and adrenaline (lignocaine 2 percent with 1:80,000 adrenaline) into the nasal mucosa.
ANAESTHESIA:
Patient requires general anaesthesia with orotracheal intubation.
It is valuable for the anaesthetist to be able to raise the CSF pressure when requested, to push the upper part of the gland into the fossa during the dissection of a macroadenoma.
POSITIONING :
The patient’s head must be stable but able to be rotated to enable convenient access to the nose with an endoscope or microscope while the surgeon is comfortably positioned.
EQUIPMENT
A standard set of nasal instruments should be supplemented with retractors that are long enough to allow direct vision of the sphenoethmoidal recess.
A self-retaining retractor (Hardy retractor) showing this view is important if a microscope is used (Fig).
If the surgeon’s preference is to use a microscope, angled eyepieces are helpful as they allow a more comfortable operating position.
A 300-mm focal length objective should be used.
If Hopkins rod endoscopes are being used, most of the surgery is done with a 0 degree endoscope,
Although 30 and 70 degree endoscopes are useful for inspecting the interior of the sphenoids and the pituitary fossa.
For opening the pituitary fossa, Angell James, Hardy or similar hypophysectomy instruments may be sufficient to dissect off the mucosa and winkle off thin bone
The two main routes to the pituitary gland are
1. Transsphenoidal and
2. Transcranial.
Transsphenoidal route is now the method of choice in 95 percent of cases.
APPROACHES TO THE SPHENOID SINUS
Various routes for transsphenoidalsurgeries are:
1. Transseptal route.
2. Transethmoidal route.
3. Transnasal route.
1. Transseptal route
This route follows the subperichondrial and subperiosteal plane to the rostrum of the vomer.
Rostrum of the vomer is removed to gain entry to the sphenoid sinuses.
This plane (subperichondrial and subperiosteal plane ) can be entered through a submucosal resection incision or through a sublabialincision.
Using the sublabial incision, periosteum over the premaxilla is incised and the piriform aperture is
exposed.
The nasal spine is exposed and the nasal mucosa is dissected off the anterior septum and off the floor of the nose using a periosteal elevator.
The dissection has to be taken far enough up both sides of the septum and across the floor of the nose to allow the quadrilateral cartilage to be displaced laterally without tearing the mucoperiostium.
Clear view of the rostrum of the vomer is achieved.
By removing rostrum of vomer an excellent view of the area of the pituitary is obtained in the midline.
This view is maintained by inserting a Hardy self-retaining retractor, which is extremely stable.
2. Transethmoidal route
Requires an incision from the medial end of the eyebrow, curved round the medial aspect of the orbit, inferiorly to the level of the upper edge of the piriform aperture of the nose.
A window is made in the medial wall of the orbit by removing the lacrimal bone in the floor of the lacrimal groove, the posterior edge of the frontal process of the maxilla and some part of the lamina papyracea.
Access is obtained through the ethmoidcomplex to the sphenoid.
The anterior wall of both sphenoid sinuses is removed to gain an excellent view of the pituitary fossa.
This view is maintained using a Talbot retractor.
Talbot retractor for the transethmoidalapproach in use showing the anterior ethmoidal artery
Transnasal route
Nose is well-vasoconstricted.
The middle turbinate is lateralized, the spheno-ethmoidal recess and the sphenoid ostium are then identified.
The anterior wall of the sphenoid sinus is removed inferiorly, widening the ostium, and then similarly in the other nostril.
An incision is made in the posterior septum about 1 cm anterior to the rostrum of the vomer, a subperiosteal dissection is made of the rostrum, which is then removed.
The rostrum is tough bone and proves valuable if the surgeon wishes to repair the defect in the anterior wall of the pituitary fossa with bone.
The transnasal route is now the preferred approach because it is quick, is suitable for use with the endoscope and causes least morbidity.
INDICATIONS FOR TRANSCRANIAL APPROACH TO
THE PITUITARY GLAND
Large intracranial element of the tumourthat is unlikely to be accessible during transsphenoidal surgery, then this approach should be considered.
Major reason for developing endoscopic pituitary tumor resection techniques is to minimize intranasal complicationsand to provide superior visualization.
The endoscopic view is panoramicwhen compared with the microscopic view.
In addition, angled endoscopes allow tumor that extends outside the sella to be seen and this improves the surgeon’s ability to achieve complete tumor resection.
Surgical Technique
Patients are catheterized prior to surgery.
This allows manipulation of fluid balance during surgery and allows the patient’s postoperative urine output to be monitored.
Standard preparation of the nose is performed with topical vasoconstriction and infiltration.
Any significant septal deviation is dealt with via either a Killian or Freer(hemitransfixion) incision.
The endoscope and microdebrider are passed medial to the middle turbinate and the superior turbinate and often the sphenoid ostium are identified (Fig)
The next step is to remove bilaterally the lower two-thirds of the superior turbinate and expose the natural ostium of the sphenoid sinus (Fig)
The sphenoidotomies are enlarged up to the lateral wall of the sphenoid.
The access provided should allow passage of an instrument below the pituitary fossaand laterally onto the internal carotid artery and optic nerve eminences. (Fig)
The next step is to remove the sphenoid mucosa starting on the sphenoid septum in the larger of the two sinuses.
The sphenoid sinus septum is removed flush with the pituitary fossa (Fig)
The thin bone of the anterior face of the pituitary is fractured and removed with a Kerrison punch (Fig)
A no. 11 scalpel blade on a no. 7 BP handle is used to create an U-shaped incision into the dura(Fig)
Malleable suction ring curettes and standard pituitary ring curettes are used to first clear the tumor along the floor of the pituitary fossa until the posterior wall of the pituitary fossa is seen (Fig)
Once the tumor has been completely removed, Gelfoam paste (Gelfoampowder mixed with saline to form a paste) is placed within the pituitary fossa.
The preserved dural flap and sphenoid mucosa are positioned over the anterior face of the sella and fibrin glue applied to the surface (Fig)
The middle turbinates are repositioned in their correct orientation and the operation is complete.
If the patient has a CSF leak from the diaphragm, then the hole in the diaphragm is identified and a conically shaped fat graft is placed into the defect and gently pushed through the hole with the malleable probe until the leak is completely sealed.
COMPLICATIONS OF SURGERY
Intraoperative complications :
1.haemorrhage,
2. CSF leak.
Early postoperative complications :
1. Diabetes insipidus,
2. CSF leak,
3. Meningitis (unusual).
Late postoperative complications :
-Persistent diabetes insipidus.
-Nasal and sinus complications.
-Recurrence of the tumour.
