28 Minimally Invasive Pituitary Surgery

Tumors of the pituitary had been described as early as 1641 by Plater, with numerous descriptions of patients with endocrine abnormalities, vision loss, and death associated with pituitary tumors, ultimately leading to the development of surgical approaches to the pituitary.1 The pituitary was first described as a glandular structure in 1688 by Brunner,² whereas the endocrine properties of the gland were detailed in 1886 by Marie.³ In the early 1900s pituitary surgeons noted a symptomatic improvement in acromegalic patients after pituitary tumor removal.² Tumors of the pituitary had been described as early as 1641 by Plater, with numerous descriptions of patients with endocrine abnormalities, vision loss, and death associated with pituitary tumors, ultimately leading to the development of surgical approaches to the pituitary.¹

Surgical Approaches to the Pituitary

Transcranial and transsphenoidal approaches^3–5 were developed during the early 20th century. Horsley performed a transfrontal approach to the pituitary in 1889,⁵ with Paul and Caton attempting resection of a pituitary tumor via a transtemporal approach in 1893.^3,6 In 1906, Horsley published a series of 10 transfrontal or transtemporal approaches.⁷ Subsequent modifications and improvements were made by neurosurgeons such as Dandy, Frazier, Heuer, and Cushing.⁷ Early transcranial approaches carried a high mortality risk from 20 to 80%,³ providing an impetus for the development of transnasal approaches. In 1897, a transglabellar approach was proposed by Giordano,^3,8 and his work laid the foundation for Schloffer, who in 1907 originated the transsphenoidal approach to the pituitary,⁹ performing a successful resection of a pituitary tumor under cocaine local anesthesia in three stages.⁷ This approach¹⁰ resulted in poor cosmesis as well as almost certain ozena, leading others to modify the technique. Cushing performed his first transsphenoidal procedure in 1909 on an acromegalic patient. After a tracheotomy, Cushing performed a modification of the Schloffer technique, making an omega-shaped incision over the forehead and creating a frontal osteoplastic flap. Under headlight illumination, ethmoidectomy was followed by sphenoidotomy, removal of the sellar floor with a chisel, and partial removal of the tumor using a curette. The patient improved and lived another 21 years.^11,12 Cushing modified the technique by incorporating a sublabial incision and submucosal resection of the septum, performing his first sublabial transseptal transsphenoidal approach in 1910 and using a 2-cm sublabial incision, submucosal septal flaps, and removal of cartilage, perpendicular plate of ethmoid, and vomer with subsequent opening of the sphenoid and sella. Cushing presented his landmark work, The Pituitary Body and its Disorders,¹⁰ then reported on 74 operations on 68 patients.⁹ Twenty-two patients experienced a slight visual improvement or stabilization of vision over months to years after the operation, whereas 22 experienced a sudden significant visual improvement. Seven deaths occurred for a mortality rate of 9.5% in that early report. Ultimately Cushing reduced the mortality rate to 5.6% later in his career.³

Surprisingly, by 1929, Cushing abandoned the sublabial transseptal transsphenoidal approach in favor of transcranial approaches citing concerns of recurrence and mortality.^3,4,13 Because of Cushing’s popularity and influence, the majority of neurosurgeons also converted to transcranial approaches. However, during this period the endonasal transsphenoidal approach was maintained by Hirsch, a rhinologist who championed the endonasal transseptal transsphenoidal. Hirsch used a head mirror for lighting with a nasal speculum and a suctioning device to enhance visualization.^4,5 Hirsch performed his first endonasal approach to a pituitary tumor on March 10, 1910, in Vienna, several weeks ahead of Cushing performing his first sublabial transsphenoidal approach. The procedure was a success with the resolution of the patient’s headaches and improvement in her vision.¹¹ Soon after, Hirsch modified his technique into a single stage with incorporation of Kocher submucous resection of the septum and by 1937 Hirsch reported a mortality rate of 5.4% in 277 patients.

With renewed interest in the transnasal approach, Dott, a neurosurgeon from Edinburgh, pioneered novel illumination techniques for pituitary surgery such as a lighted speculum.³ French surgeon Guiot learned the technique from Dott and performed more than 1000 surgeries, introducing intraoperative fluoroscopy to help define the anatomy of the nasal passages.^3–5,8 Hardy revolutionized the transsphenoidal pituitary surgery by introducing the use of the operating microscope and microsurgical instrumentation in 1967,^3,5 which permitted a more thorough and safer resection of macro- and microadenomas without deaths or major morbidities.³

Introduction of Endoscopic Pituitary Surgery

The endoscope and its use by otolaryngologists to treat inflammatory sinus disease as championed by Kennedy, Stammberger, and others grew in the early 1990s. With its clarity of view and brightness of visualization the endoscope was quickly adopted for transsphenoidal pituitary surgery.3

Guiot initially reported the use of the endoscope as a complementary tool during the microscopic sublabial transseptal approach; however, with the exception of Bushe and Halves, no other descriptions of endoscopic transsphenoidal pituitary surgery appeared until 1992 when Jankowski reported the first such procedure in three patients.^3,14 Jho and Carrau in 1997 reported on the first large series of 46 patients managed endoscopically, demonstrating the safety, efficacy, and advantages of this technique¹⁵ and marking the initiation of the modern minimally invasive pituitary surgery (MIPS) era.

Technological advances such as high-resolution computed tomography (CT), magnetic resonance imaging (MRI), and stereotactic navigational guidance systems¹⁶ have significantly improved assessment of the sella, tumor extent, and tumor localization. Endoscopes allow for visualization with close proximity to the operative field and multiple visual angles. Use of endoscopes in MIPS approaches reduces operative time^17–19 with superior illumination and magnification,^19–21 diminished blood loss,²² enhanced differentiation between normal gland and tumor,²³ better intrasellar and parasellar images,²⁴ reduced hospital stay, improved patient satisfaction, and decreased need for packing.²⁵ The MIPS approach alleviates the need for external incisions, while minimizing septal perforations and postoperative nasal obstruction.^19,25 The binocular visualization provided by the microscope is lost in the MIPS technique. Many neurosurgeons have not been trained in the use of the endoscope, which leads to a learning curve for the novice. A joint effort by the otolaryngologist and the neurosurgeon is favored for resection of pituitary tumors; this allows for a safe and rapid approach in which each surgeon performs that part with which they are most comfortable.

Anatomical Considerations

The pituitary gland sits in the sella turcica on the superior aspect of the sphenoid bone. It is located behind the tuberculum sellae, which is located posterior to the optic chiasm. The posterior boundary of the sella is defined by the dorsum sellae and posterior clinoid. Below the dorsum sellae is the clivus, which slopes inferiorly and is continuous with the occipital bone.²⁶ The lateral extensions of the tuberculum sellae form the anterior clinoid processes. The roof of the fossa is formed by the diaphragm, a dural fold traversed by the pituitary stalk. The lateral extension of the diaphragm forms the roof of the cavernous sinus.²⁶

The pituitary gland lies in close proximity to the optic chiasm and nerves, the carotid arteries, cranial nerves III to VI in the cavernous sinus, as well as the basilar artery and brainstem posteriorly. Proper knowledge of this parasellar anatomy is essential to performing these approaches.

The sphenoid sinus is variably pneumatized with three types of sphenoid pneumatization patterns described: conchal (minimal pneumatization with thick bone over the face of the sella), sellar (pneumatized to the face of the sella), and postsellar (pneumatization beyond the face of the sella). The majority of adult sinuses are of the sellar type and postsellar type.²⁶

Asymmetry of the two sphenoid cavities is the norm, and multiple septations may be present.²⁷ The roof of the sinus is formed by the planum sphenoidale anteriorly and the sella posteriorly. The posterior wall corresponds to the clivus and, superiorly, the face of the sella. In the sella, the lateral walls form the medial walls of the cavernous sinus. Intercavernous venous connections usually run inferior to the gland but can run anteriorly and may be a source of bleeding intraoperatively when the dura is incised. The canal of the vidian nerve runs laterally along the sphenoid floor, and the carotid arteries run laterally at about 5- and 7-o’ clock position. The optic nerves run superiorly along the lateral walls, at about 2- and 11-o’ clock position, with the opticocarotid recess located between the bulges of these two structures.¹⁵

Surgical Indications

Indications for excision of nonsecreting adenomas include large size or evidence of rapid growth, compressive symptoms, hypopituitarism, visual changes, pituitary apoplexy, or severe headaches. Patients with secreting prolactinomas are referred for surgery after failure of medical management. Patients with acromegaly, hypothyroidism, Cushing disease, Rathke cleft cysts (RCCs), chordomas, and arachnoid cysts are offered primary surgery.

Preoperative Evaluation

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