Transsphenoidal hypophysectomy

Standard treatment for nonfunctioning pituitary adenomas.

Transsphenoidal hypophysectomy, is a surgical procedure for resectioning tumors of the pituitary gland.

Pituitary surgery or hypophysectomy has evolved to a fully endoscopic endonasal procedure through the sphenoid sinuses. 

Approaches to the pituitary gland can be broadly classified into transcranial and extracranial approaches. 

Transcranial microscopic approaches, used currently in cases where transsphenoidal approaches are contraindicated, involve anterior subfrontal and frontotemporal approaches. 

Pterional (frontotemporal)approach, which involves removing the sphenoid wing and minimal brain retraction, provides the shortest trajectory to the parasellar region and excellent visualization of the pituitary gland,and has the advantage of straight visualization of the pituitary tumor between the optic nerves: It has potential damage to olfactory nerves and frontal sinuses.

Extracranial approaches primarily consist of transsphenoidal microscopic approaches, transnasal or sublabial, and endoscopic transnasal transsphenoidal approach, along with modifications such as expanded endoscopic endonasal approach (EEEA) and combined transsphenoidal transmaxillary approach. 

Transsphenoidal microscopic approaches used the sublabial or septal incisions are associated with significant morbidities, such as facial swelling and pain, regular need for nasal packing or septal splints, sinonasal complications such as sinusitis, numbness of the upper alveolus, nasal synechiae, and septal perforation.

Endoscopic pituitary surgery uses the natural medial nasal corridor to assess the sphenoid sinus, and has shorter hospital stays, panoramic view, and good mobility with angled views.

Endoscopic transsphenoidal hypophysectomy has extended anterior skull base approaches.

The pituitary gland lies in a saddle-shaped depression in the body of the sphenoid bone, known as the sella turcica/pituitary fossa. 

The floor of the pituitary fossa forms the roof of sphenoid sinuses posteriorly. 

The optic chiasma is located posterosuperior anterior to the pituitary stalk.

Sphenoid sinuses are approached via passing the endoscope in a medial corridor, between the nasal septum and middle turbinate.

The structures encountered in a well-pneumatized sphenoid sinus are the optic nerve, carotid artery, and sella turcica. 

The pituitary fossa in the midline is flanked by the cavernous sinus and the cavernous segment of the carotid artery. 

The optic nerve is located at the junction of the sidewall and roof, as the carotid arteries are followed superiorly. 

Above the pituitary fossa is the tuberculum sella.

The presence of any anatomical variations makes endonasal transsphenoidal access difficult: 

septal deviation or prior septal surgery, sinonasal disease or nasal polyps.

The optic nerve canal is dehiscent in 4% to 8% of cases.

The risk of injury to the carotid artery is around 5% in pituitary surgery and higher in para-sellar surgery.

Pituitary adenomas, both micro and macroadenomas, are the most frequent indication for transsphenoidal hypophysectomy. 

Surgery is indicated for nonsecreting adenomas that cause vision disorders, hypopituitarism, pituitary apoplexy, or demonstrate the progression on serial imaging. 

Surgery is recommended for secreting adenomas that do not respond to medical management. 

Other sellar lesions can be approached similarly, such as Rathke’s cyst, craniopharyngiomas, meningiomas, chordomas, or metastatic lesions.

The transsphenoidal surgical management contraindicated in: sphenoid sinusitis, intrasellar vascular anomalies, ectatic midline carotid arteries, or significant lateral suprasellar extension of tumor.

Relative contraindications include:  poorly pneumatized sphenoid sinus, significant suprasellar adenoma extension, and constrictive diaphragma sellae.

Intraoperative MRI benefits pituitary surgery, providing updated images showing the change in tumor volume, the dura, and normal pituitary.

Otolaryngologists can greatly enhance the speed of surgery and provide access in cases with difficult anatomies, such as the deviated nasal septum, nasal polyps, or unpneumatized sella.

The otolaryngologist exposes the dura over the sella, and then the neurosurgeon opens the dura, followed by removing the tumor. 

Preoperative evaluation with a full head and neck exam, vision examination, visual acuity, perimetry, gaze restriction, preoperative nasal endoscopy to rule out anatomical obstruction or sinusoidal disease, and evaluation of the pituitary function and hormone status 

Inadequate pituitary reserve before surgery would increase the risk of hypopituitarism in the perioperative period. 

Preoperative baseline pituitary function

can identify patients in whom medical therapy would  needed.

Measurement of growth hormone (GH), cortisol, serum prolactin, triiodothyronine, thyroxine, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) are done. 

Imaging, in the form of CT scan and magnetic resonance imaging (MRI) scan,  help  define  sellar pathology and planning surgical approach. 

MRI is superior to CT scan due to its greater soft-tissue contrast, which allows the delineation of vital structures such as optic chiasm, intracavernous carotid arteries, optic nerves, and cavernous sinuses. 

MRI allows an understanding the exact tumor extension, tumor composition, and differentiating mass from obstructed fluid/mass, and information on dural involvement or invasion.

Microadenomas are hypointense to the pituitary gland and enhance less than the normal gland, with an early washout.

Macroadenomas are usually hypointense or isointense to grey matter, but on postcontrast images, enhance well, making them easy to diagnose.  

Pituitary adenomas are isointense to brain parenchyma on CT without contrast. 

They show intense enhancement with contrast. 

CT scans can demonstrate bony erosion and expansion of the sella accurately. 

CT scans aid in the planning of the surgical approach: identifying  septal deviations, sinonasal disease or nasal polyps, the extent of pneumatization of sinuses, ease of transnasal access to the sphenoid sinus, and anatomical variations, aberrant carotid artery, or bony dehiscences at the skull base.

Catheterization is mandatory for accurate fluid balance management, especially with the risk of diabetes insipidus. 

The sphenoid ostium is identified and widened to lamina papyracea. 

The normal pituitary gland appears yellow and is solid.

Pituitary adenomas appearsamorphous and white. 

An extracapsular resection of the tumor is attempted. 

A multilayer closure and complete defect coverage are critical. 

Tissue grafts are commonly used to reconstruct small to moderate skull base defects and for low-flow CSF leaks. 

Endoscopic pituitary surgeries are safer compared with established complication rates of microsurgical approaches of transcranial or sublabial, though there is no difference in the efficacy between these approaches.

Complications can occur at every stage of operation.

Complications during the nasal stage of the approach are orbital injury, saddle nose deformity, anosmia, cribriform plate injury with CSF leak, and bleeding from injury to the sphenopalatine artery and its branches. 

Complications arising in the sphenoid sinus are sinusitis, injury to the carotid artery or optic nerve, and mucoceles. 

Complications encountered during tumor removal include CSF leak, diabetes insipidus, hypopituitarism, meningitis, postoperative hematoma, injury to the carotid artery or optic nerve, vasospasm, ophthalmoplegia, subarachnoid hemorrhage, and tension pneumocephalus. 

The most common complications of transphenoidal hypophysectomy are: CSF leak, sinusitis, meningitis,  worsening of vision as a result of bleeding or manipulation and arterial hemorrhage.

CSF leaks, occurring in 6 in every 100 cases.

CSF leaks are usually prevented by a multilayer closure at the end of surgery.

Carotid artery injury

Nasal congestion and mild nasal bleeding are anticipated in the immediate first 1 to 2 weeks after surgery, along with pain over the nasomaxillary region, nasal crusting, mucosal scarring, periorbital edema, and numbness of the upper incisors. 

The presence of nasal splints or packs often compounds postoperative morbidity.  

Mucosal damage can lead to sinusiti,  and hyposmia. 

Long-term complications include nasal synechiae and septal perforation, and atrophic rhinitis.

The most common endocrine complications in early postoperative period: is abnormalities of antidiuretic hormone (ADH) secretion, which includes diabetes insipidus (DI) and inappropriate secretion of antidiuretic hormone (SIADH). 

Diabetes insipidus is the most common endocrine complication after pituitary surgery, with the postoperative incidence ranging between 5% and 35%.

Postoperative diabetes insipidus is often manifests as a triphasic response: polyuria and polydipsia occurring in the first 48 hours and last a few days. 

Antidiuresis and hyponatremia develop, commonly after 1 week of surgery. 

A polyuric phase, ending in permanent DI. 

Generally, diabetes insipidus resolves spontaneously without any specific therapy within 24 hours. 

Surgical lesions located in the pituitary stalk or above the median eminence are prone to permanent diabetes insipidus.

in the event of unresolved DI, therapy is stepped up, ranging from fluid replacement with 5% dextrose to the administration of synthetic ADH analog, desmopressin. 

Intranasal desmopressin is the drug of choice for chronic cases of DI.

Syndrome of inappropriate ADH (SIADH) is the most common cause of hyponatremia after pituitary surgery and occurs in 9% to 30 % of patients undergoing a transsphenoidal approach.

Most patients with SIADH are asymptomatic, and are diagnosis is detected on the serum electrolyte panel done on postoperative day 7.  

Postoperative SIADH is treated based on the degree of hyponatremia, presence of symptoms, and comorbid conditions. 

Fluid restriction and, occasionally, salt administration are the mainstay of therapy, and can be managed on an outpatient basis with serial sodium and fluid output monitoring. 

Correction of sodium levels may take up to 5 days. 

Symptomatic patients are hospitalized and managed with intravenous 3% saline. 

Hyponatremia is the most frequent cause of unplanned readmission after pituitary surgery due to SIADH: usually presents after postoperative day 5.

The management of postoperative hypopituitarism involves adequate glucocorticoid replenishment with fluid and electrolyte replacement. 

The glucocorticoid doses are tailored in the perioperative period and subsequently tapered to preoperative doses. 

Postoperatively, the patients are monitored for neurological deterioration, epistaxis, visual dysfunction, diabetes insipidus, and hypotension secondary to acute hypocortisolism. 

Desmopressin and/or steroid replacement need to be continued postoperatively if the patient was already taking these agents.

The majority of patients undergo MRI after three months of the procedure.

Transsphenoidal hypophysectomy is an effective surgical technique for removing pituitary and other intrasellar tumors with minimal morbidity and hospital stay. 

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