User:Jlukeedwards/sandbox/Endoscopic Endonasal Surgery

Endoscopic Endonasal Surgery is a minimally invasive technique used mainly in neurosurgery and in otolaryngology. It involves a neurosurgeon or otolaryngologist using an endoscope that is entered through the nose to fix or remove any brain defects or tumors in the anterior skull base. Normally the otolaryngologist performs the beginning of the surgery when the surgeons are going through the nasal cavity and sphenoid bone, and the neurosurgeon takes over before drilling into any cavities containing a neural organ like the pituitary gland. Although the surgery is minimally invasive, the technique still requires an expert level of familiarity. These type of procedure or technique is normally done when the the brain defect or tumor is located in an area that is difficult to access or when the doctor wants to reduce the postoperative recovery time of their patient.

History of Endoscopic endonasal surgery
The first person to use the term, endoscope, was a urologist in Paris by the name of Antonin Jean Desomeaux. The endoscope was first invented, however, in the 1800s when a physician in Frankfurt, Germany by the name of Philipp Bozzini wanted to see the inner workings of the body, and this device would become the precursor to the modern endoscope. He called his invention a Light Conductor (Lichtleiter in German). He later wrote about his experiences on live patients with this device that consisted of an eyepiece and a container for the candle light. This prompted the University of Vienna to take up the device to test its practicality in medicine. After getting negative results for trials on live humans and being forgotten, Maximilian Nitze and Joseph Leiter used the invention of the light bulb by Thomas Edison to make a more refined endoscope. This iteration was used for urological procedures and eventually otolaryngologists began to use their device for eustachian tube manipulation and removal of foreign bodies. Then further iterations were made by Hisrchmann, Harold Hopkins, Karl Storz, and Walter Messerklinger, who brought it to the US by showing teaching David Kennedy at Johns Hopkins how to use it.

The transphenoidal and intracranial approaches to pituitary tumors began in the 1800ss, but with little success. A man by the name of Gerard Guiot popularized the transphenoidal approach leading to it becoming a part of the neurosurgical curriculum. Gerard Guiot was the very first neurosurgeon to use an endoscope for a transsphenoidal surgery, however he discontinued the use of this technique because of inadequate sight. In the late 1970s, the endocopic endonasal approach was used to augment microsurgery, to view things that were out of their line of sight. A surgeon named Axel Perneczky, who is considered to be a pioneer of endoscopy used in neurosurgery, said that endoscopy "improved appreciation of micro-anatomy not apparent with the microscope."

Endoscopic Instrumentation
The endoscope always consists of these basic parts: mechanical housing, glass fiber bundles for cold light illumination, and optics and these different views: 0 degree for straight forward, 30 degrees for forward plane, 90 degrees for lateral view, and 120 degrees for retrospective view. For endoscopic endonasal surgery, the rigid rod-lens scopes are used because of their better quality of vision. The endoscope itself has an eyepiece that the surgeon could look through, but the surgeon normally does not use this because it requires the surgeon to be in a fixed position. Instead they use a video camera that broadcasts to a monitor that shows the entire surgical field in front of the endoscope.

Areas of Interest for Surgical Planning
Before surgery can begin, several other specialties need to be involved to decide what the absolute best surgical plan may be. Tumors on the skull base require a team of doctors normally an Endocrinologist, a Neuroradiologist, an Ophthalmologist, a Neurosurgeon, and an otolaryngologist. The bulk of the work for the first three are done before surgery.

Endocrinology
The role of an endocrinologist that is on a team preparing for an endoscopic endonasal surgery normally is only involved if the tumor is located on or touching the the pituitary gland. They then try to use pharmacology to treat the tumor by either controlling the levels of hormone that the pituitary gland secretes or reducing the size of the tumor. If this is not enough that is when the patient is refereed to surgery. The main types of pituitary adenomas are:


 * PRL-secreting or prolactinomas: These are the most common type of pituitary tumors. They are normally associated with infertility, gonad, and sexual dysfunction because they increase the secretion of prolactin or PRL. The drugs that endocrinologist use are brimocriptine (BRC), which normalizes PRL levels and has been shown to lead to tumor shrinkage. They also use quinagolide (CV) or cabergoline (CAB) as dopamine or D2 antagonists to treat these tumors. Endoscopic endonasal surgery is normally done as a last resort when the tumor is either resistant to the drugs, there is no tumor shrinkage or the PRL levels cannot be normalized.
 * GH-secreting: These are very rare, but result in the increase in the secretion of growth hormone. There are about 50-80 cases per million people and 3-4 new cases per million people every year. Interestingly, these type of tumors constitute 16% of the pituitary tumors that are done. The tumor normally results in the acral enlargement, athropathy, hyperhidrosis, changes in facial features, soft tissue swelling, headaches, visual changes, or hypopituitarism. With this type of tumor pharmacological therapy has had little affect. For that reason, a trans-sphenoidal adenoectomy is the first option for this type of tumor.
 * TSH-secreting: This type of tumor is related to the increase in the secretion of the thyroid-stimulating hormone. This leads to hyperthyroidism which leads to headaches and visual disturbances. However, they are very rare and only account for 1% of pituitary surgeries. First, they are treated surgically, but that has does not normally cure the patient completely. They are then treated by somatostatin analogues because TSH related tumors increases the expression of somatostatin receptors.
 * ACTH-secreting: This tumor is related to the increased secretion of adrenocorticotropic hormone or ACTH, and is Cushing's disease and leads to Cushing's syndrome. This type of tumor is managed poorly by pharmacology so surgery is the best option. The removal of the tumor from the sella results in an 80%-90% cure rate.

Neuroradiology
The main job of a neuroradiologist is to take images of the defect so that the surgeon can know more about what he or she is going to see when they start surgery. This includes identifying the lesion, controlling the effects of the medical therapy, defining the spatial situation of the lesions, and verifying the removal of the lesions. The lesions associated with endoscopic endonasal surgery normally include:


 * Pituitary Microadenomas
 * Pituitary Macroadenomas
 * Rathke's cleft cysts
 * Pituitary inflammatory disease
 * Pituitary metastases
 * Empty Sella
 * Craniopharyngiomas
 * Meningiomas
 * Chiasmatic and Hypothalmic gliomas
 * Germinomas
 * tuber cinereum hamartomas
 * Arachnoid cysts
 * Neurinomas of the trigeminal nerve

Opthalmology
The problem with some of the suprasellar tumors are that they start to invade the chiasmatic cistern, which leads to impaired vision. When this happens, an ophthalmologist has to be brought in to make sure everything goes right or corresponds to maintaining optic health including pre-surgical treatment, advising proper surgical technique to make sure the optic nerve is not in danger, and post-surgery care of the eyes. The common types of problems include:
 * Visual Field defects
 * reduced visual activity
 * VEP abnormalities
 * dischromatopsy
 * eye motility impairment

Transnasal Approach
The transnasal approach is used in cases when the surgeon wants to real the roof of the nasal cavity, the clivus, or the odontoid. This would most likely be to remove chordomas, chondrosarcoma, inflammatory lesions of the clivus, or metastases in the cervial spine region. The anterior septum or posterior septum are removed to allow access to these areas and so that the surgeon can use both sides of the nose for a microscope and instrument or two surgical instruments.

Transsphenoidal Approach
This type of procedure is the most common and the most useful technique of endoscopic endonasal surgery. That is because it is the procedure that takes a surgeon to the seller space or the sella turica. The sella is basically a cradle inside of which the pituitary gland sits, so if you have a pituitary adenoma this is the procedure the surgeon would use to reach the tumor under normal circumstances. The surgeon uses a transnasal approach to start the transsphenoidal approach to the sphenoid ostium, which is located on the anterosuperior surface of the sphenoid sinus and acts as a portal into this sinus. Then the anterior wall of the sphenoid sinus and the sphenoid rostrum is removed to allow the surgeon a panoramic view This procedure also goes with the removal of the posterior septum to allow the use of both nostrils in surgery. Since the surgeon comes into the sphenoid from behind it, they have to go through the cavernous sinus. This poses a biggest challenge for the surgeon because of its intense neurovasculature. In this area there are several triangles of blood vessels that make traversing this region very difficult. These include the anteromedial triangle, the paramedical triangle, the Parkinson's triangle and the lateral triangle. It is import that surgeons understand these areas to increase surgical success rate. A surgeon typically would use stereotactic imaging and a micro Doppler to help them during the surgery.

The invention of angled scopes allows for the surgeon to go beyond the sella to the suprasellar region. This is done with the addition of the transstuberculant approach and transplanum approach to reach the suprasellar cistern, lateral approach to the medial cavernous sinus and petrous apex, or with the inferior approach to the superior clivus. The main worry here is that the Perneczky triangle is treated well this triangle is made up of optic nerves, cerebral arteries, the third cranial nerve, and the pituitary stalk, which damage to any of these could provide a devastating outcome from surgery.

Transpterygoidal Approach
The Transpterygoidal approach is described as going through the posterior edge of the maxillary sinus ostium and posterior wall of the maxillary sinus. This includes going through three separate sinus cavities: the ehmoid, the sphenoid, and the maxillary sinuses. One would use this method to reach the cavernous sinus, lateral sphenoid sinus, infra temporal fossa, pterygoid fossa, and the petrous apex. This occurs by a uninectomy (removal of the osteomeatal complex), medial maxillectomy (removal of maxilla), ethmoidectomy (removal of ethmoid cells and/or ethmoid bone), sphenoidectomy (removal of part of sphenoid), and then removal of the maxillary sinus and the palatine bone. The posterior septum is also removed at the beginning to allow use of both nostrils.

Transethmoidal Approach
This approach makes a surgical corridor from the fontal sinus to the sphenoid sinus. It is done by the complete removal of the ethmoid bone, which allows a surgeon to expose the foveal ethmoidalis and the lamina papyracca or medial orbital wall laterally. This procedure may be successful in the removal of small encephalocetes of the ethmoid osteomas of the ethmoid wall or small olfactory groove maningiomas, but with larger tumors or lesions, one of the other techniques above is required.

Approach to Sellar Region
This procedure starts off with the patient being anesthetized and prepped. If the surgery is for a smaller tumor one nostril is used, but for larger tumors two nostrils are used so the posterior nasal septum has to be removed. Then the surgeon slides the endoscope into the nasal choana until he or she finds the sphenoid ostium on the anterior side of the sphenoid. The doctor then cauterize the mucosa around the ostium for microadenomas and remove the mucosa completely for macro adenomas. The doctor then enter the ostium and meet the sphenoid rostrum where the surgeon retracts the mucosa of this structure and removes the sphenoid sinus septum to make the surgical pathway. At this point, imaging and Doppler devices are used to define the important neurological structures in the sphenoid. Then the floor of the sella is opened with a high speed drill being careful to not pierce the dura. When the dura is visible, it is cut with a cruciate incision to make sure only the dura is cut. The area where the tumor is located is then carefully palpated by the surgeon's surgical instrument that extends through the endoscope. If the tumor is small, the tumor can be removed by an en bloc procedure which consists of cutting the tumor into many sections for removal. If the tumor is larger, the center of the tumor is removed first, then the inferior, then lateral, then superior to make sure that the arachnoid membrane does not expand into surgical view. This will happen if the superior part is taken out too early. After tumor removal, the surgeon checks for CSF leaks using a florescent dye, and if there is no leak, he or she closes the area.

Approach to Suprasellar Region
This technique is the same as to the sella region but when they get to the side of the sella that touches the tuberculum sellae. Instead of drilling into the sella, the surgeon drills into the tuberculum sellae, the surgeon then makes an opening that extends halfway down the sella to expose the dura, and the intracavernous sinus is exposed. The planum sphenoidal is then removed to show the optic chiasm, optic nerve, and pituitary gland. Then pushing apart the pituitary gland and optic chiasm, one can see the pituitary stalk, and behind this stalk, there is the basilar tip, posterior cerebral arteries, mammillary bodies in the interpeduncular cistern. Then to better see the tumor a bilateral posterior ethmoidectomies. The dura is then cut and the tumor is removed. These types of tumors are separated into two types:


 * Prechiasmal Lesions: This tumor is normally staring the surgeon right in the face when he or she cuts the dura. The tumor is internally decompressed. After decompression, the tumor is removed taking care to not disrupt any optic nerve or major arteries.


 * Postchiasmal Lesions: This time the pituitary stalk is in the front because the tumor is pushing it towards the area the dura was opened. Dissection then starts on both sides of the stalk to preserve pituitary-hypothalmic axis and below the chiasm and above pituitary gland to protect the stalk. The tumor is carefully removed and the patient is closed up.

Approach to Orbital Apex
This approach uses the transethmoidal approach. It starts with a septoplasty, which straightens out the septum or the septum could be completely removed to allow for both nasals to be used. Then a unicintectomy and complete sphenoethmoidectomy is performed to make the surgical corridor, and for this surgery a large visual field is needed. Then the surgeon will identify the medial wall of the orbital apex, which is drilled down to be opened. The lesion is the biopsied and removed or biopsied and left alone. The surgeon then closes after reconstructing the hole that was made from surgery so that no CSF leak occurs.

Skull Base Reconstruction
The base of the skull is one of the most difficult areas to access for a neurosurgeon because of the serious complications that could arise post-operation. When there is a tumor, injury, or some type of defect at the skull base whether the surgeon used an endoscopic or open surgical method, the problem still arises of providing separation of the cranial cavity and sinonasal cavity to prevent cerebrospinal fluid leakage.

For this procedure, there are two ways to start the procedure with a free graft repair or with a vascularized flap repair. The two techniques are free graft repair and local or regional vascularized flaps for the reconstruction phase of the surgery. The free grafts use materials such as accelular dermis, turbinate mucosa, cadaveric pericardium, fascia lata, and titanium mesh to repair the skull base defects, which is very successful (95% without CSF leaks) with small CSF fistulas or small defects. It is basically removing a material completely from its original location or it is completely free of its original location, and that flap is then placed onto a completely different location (the skull base in this case). The local or regional vascularized flaps are pieces of tissue relatively close to the surgery site that have been mostly freed up but are still attached to the original tissue. These flaps are then stretched or maneuvered onto the desired location. The free graft repair was the most widely used procedure because of its success with smaller defects. When technology advanced and larger defects could be fixed endoscopically, more and more failures and leaks started to occur. This sparked the move towards the vascularized flaps protocol in hopes of preventing this major post-op complication. The larger defects are associated with a wider dural resection and an exposure to higher flow CSF within the cistern, which could be the reason for failure among the free graft.

Pituitary Gland Surgery
This type of surgery is one of the most common types of surgery that use the endoscopic endonasal surgical technique. Mainly because it has had a lot of success because it turns the very serious surgery that could scar a person's face or leave them with a long recovery time into a minimally invasive through the nose surgery. For instance craniophatyngiomas are starting to be removed via this method. Dr. Paolo Cappabianca described the perfect one for this surgery to be a midian lesion with a solid parasellar component or encasement of the main neuromuscular structures that are localized in the subchiasmatic and retrochiasmatic regions. He also says when these conditions are met endoscopic endonasal surgery is a valid surgical option. For a case study on large adenomas, the doctors showed that out of 50 patients, 19 had complete tumor removal, 9 had near complete removal, and 22 had partial removal. The partial removal came from the tumors extending into dangerous areas. They concluded that endoscopic endonasal surgery was a valid option for surgery if the patients used pharmacological therapy after surgery. Then in another study it showed that with endoscopic endonasal surgery 90% of microadenomas could be removed, and that 2/3 of normal macroadenomas could be removed if they did not go into the cavernous sinus which means the doctor would have to deal with the P triangle so only 1/3 of those patients recovered.

3-D Approach vs 2-D Approach
The newer 3-D technique is gaining ground as the ideal way to do surgery because it gives the surgeon a better understanding of the spatial configuration of what they are seeing on a computer screen. Dr. Nelson Oyesiku at Emory University helped develop the 3-D technique. In an article he helped write, he and the other authors compared the effects of 2-D vs 3-D technique on patient outcome. It showed that the 3-D endoscopy gave the surgeon more depth of field and stereoscopic vision and that the new technique didn't show any significant changes in patient outcomes during or after surgery.

Endoscopic VS Open Techniques
In a case study done in 2013, they compared the open vs endoscopic techniques for 162 other studies that contained 5,701 patients. They only looked at four tumor types the olfactory groove meningiomas (OGM), tuberculum sellae meningiomas(TSM), craniopharyngiomas (CRA), and clival chordomas(CHO). They mainly looked at gross total resection and cerebrospinal fluid (CSF) leaks, neurological morbidity, post-operative visual function, post operative diabetes insipidus, and post-operative obesity. The study showed that there was greater chance of CSF leaks with endoscopic endonasal surgery. The visual function improved more with endoscopic endonasal surgery for TSM, CRA, and CHO patients. That the rate of diabetes insipidus was a lot higher in patients that had an open procedure. The endoscopy patients showed a higher recurrence rate. In another case study on CRAs, they showed similar results with the CSF leaks being more of a problem in endoscopy patients. They showed that open procedure patients showed a higher rate of post operative seizures as well. Both of these studies still suggested that despite the CSF leaks which are improving that the endoscopic technique is still a very suitable surgical option.