Visual Function after Minimally Invasive Pituitary Surgery (MIPS)

Kuruvilla R, Ewend MG1, Senior BA2, Givre SJ3,4

 

1Department of Neurosurgery, 2 Otolaryngology, Head and Neck Surgery,  3Ophthalmology, and 4Neurology
University of North Carolina, Chapel Hill, NC

 
 

Introduction

Among other complications, patients with pituitary adenomas can have loss of the peripheral vision in one or both eyes due to physical compression of the optic chiasm.  Surgery to remove these lesions has traditionally been performed through a sublabial or endonasal transsphenoidal approach.  A microscope is used to obtain visualization throughout the procedure.  Although an open microscopic approach is effective and time-tested with regard to tumor resection, complications may be associated with this technique including permanent upper lip numbness, nasal septal perforation, post-operative epistaxis and need for nasal packing.   

Recently an entirely endoscopic approach to pituitary tumor resection, termed minimally invasive pituitary surgery (MIPS), has been used as an alternative to traditional surgery.  The endoscopic approach enables access to the tumor via a 4 mm endoscope which travels through one of the nasal passages between the middle and superior turbinates without requiring septal fracture to accommodate its width.  Surgical instruments are inserted adjacent to the endoscope, through the same nostril in most cases.  The superior turbinate is used as the landmark for identification of the sphenoid ostium.  Upon visualization of the anterior face of the sphenoid sinus, sphenoidotomy is performed and the sinus is entered.  The intersinus septum and sphenoid rostrum are then removed to allow access to the sella turcica.  Once the sellar face is fenestrated, the dura is opened and the tumor is removed with a combination of curettes and microsuction devices.  After resection, angled endoscopes are used to inspect for residual tumor and cerebrospinal fluid (CSF) leaks.  Unless a CSF leak is noted, no infraumbilical fat graft, lumbar drainage, or nasal packing is used.   

As compared with conventional surgery, MIPS results in fewer minor complications and shorter post-operative hospital stays.1  In addition, endoscopic surgery provides better anatomical exposure, potentially allowing more complete resections.1  Preservation and restoration of vision are important goals in pituitary surgery.  In order for MIPS to be accepted along side traditional approaches, visual outcomes following MIPS must be comparable to those from conventional surgery.  This study evaluates visual function outcomes in patients undergoing MIPS. 

Methods:

The current study is a retrospective review of patients undergoing MIPS who had ophthalmologic examination including measurement of visual acuity, confrontation visual fields, when possible, formal visual field testing (automated threshold or Goldmann perimetry), pupil testing and observation of the optic discs before and after surgery.  MIPS was performed by a single team of surgeons.  Pre- and postoperative ophthalmologic examinations were compared.  Automated threshold perimetry was scored using a system similar to that used in the Collaborative Initial Glaucoma Treatment Study.2  In the current system, scores are based on the probabilities in the total deviation plot and are calculated as follows: Each of the points in the field is individually graded. A point is called defective if its probability is 0.05 or less and it has at least two neighboring points (neighboring defined as adjacent, whether on a side or a corner) with probabilities of 0.05 or less. A weight is assigned depending on the depth of the defect at the given point and the two least defective neighboring points. Minimum defects of 0.05, 0.02, 0.01, and 0.005 are given weights of 1, 2, 3, and 4, respectively. A point without two neighboring points both depressed to at least p < 0.05 is given a weight of zero. For example, a point at p < 0.01 with two neighboring least defective points of defect both at p < 0.05, would receive a weight of 1. The weights for all points in the field are summed.   

Results

Eighteen patients were evaluated.  Fifty-five percent were men, 44% were Caucasian, 39% were African-American and 6% were Asian or Hispanic.  Patients ranged in age from 21 to 73 years (mean 47.4) at the time of surgery.  The duration between surgery and post-operative ophthalmologic examination ranged from 2 to 60 months (mean 16.5).  The results for individual patients are presented in Table 1.  Data printed in red denote postoperative improvement; data printed in green denote post-operative worsening. 

Thirty-one eyes had visual fields pre- and postoperatively that were comparable either by visual field score or subjective assessment.  Of these eyes, 5 had normal pre-operative visual fields and 26 had abnormal pre-operative visual fields.  Of these 26 eyes with abnormal visual fields, 22 improved, 3 worsened and 1 was unchanged.  Twenty-seven eyes had pre-operative visual acuity better than or equal to 20/25.  Eight eyes had vision worse than 20/25 and one eye was NLP unrelated to the tumor.  Seven of 8 eyes with preoperative visual acuity worse than 20/25 improved by two lines or more.   One eye with hand motions vision pre-operatively was unchanged after surgery.  No patient’s visual acuity worsened two lines or more after surgery. 

Discussion

One of the objectives of pituitary surgery is to prevent or halt progressive visual loss.  In addition, many patients who have lost visual function from these tumors achieve some or complete recovery after surgery.  Multiple studies of visual recovery after non-endoscopic transsphenoidal pituitary surgery have shown excellent results with this technique.3-5  Powell5 reviewed the visual outcomes of 67 patients who underwent conventional transsphenoidal surgery and found that of those with pre-operative visual field loss, 77% improved after surgery, 34% to normal.  Forty-five percent of patients with abnormal visual acuity before surgery had improvement.  Both Marcus and colleagues4 and Sullivan and colleagues3 found similar results.  The current retrospective case series is a preliminary evaluation of visual outcomes in patients with pituitary adenomas undergoing a new technique for resection: endoscopic endonasal transsphenoidal pituitary surgery (MIPS).  Minimally invasive pituitary surgery has been shown to be an acceptable alternative to conventional surgery in terms of complications rates and may be the preferred surgical method in terms of length of hospital stay, necessity for nasal packing and necessity for lumbar drainage.1  The visual outcomes in patients undergoing MIPS have not been well studied.  However, for MIPS to become an accepted surgical technique, visual outcomes in patients undergoing this procedure must at least equal those of patients undergoing conventional surgery.  In the current study, visual acuity  and visual fields were measured in patients with pituitary adenomas before and after MIPS.  87.5% of eyes with pre-operative visual acuity worse than 20/25 but better than NLP had improvement in visual acuity.  84.6% of eyes with abnormal pre-operative visual fields had improvement after surgery.   

Previous reviews of visual outcomes after conventional surgery primarily used subjective scoring of Goldmann visual fields as the main assessment parameter.  The current study employed automated threshold perimetry and a more objective scoring method when possible.  Though the ability to directly compare the results of automated threshold perimetry to Goldmann perimetry is limited, the use of automated threshold perimetry in the current study likely accurately reflects the most common current clinical practice for evaluating patients with pituitary adenomas. One limitation of our study and previous studies in assessing visual field outcomes after pituitary surgery is that some post-operative improvement might be expected based on familiarity with taking the test rather than an effect of surgery.  Given these limitations our preliminary results show that MIPS may be a good alternative to traditional pituitary surgery.  Assessment of visual function in patients undergoing MIPS is ongoing. 
 

References:

1. White DR, Sonnenburg RE, Ewend MG, Senior BA. Safety of minimally invasive pituitary surgery (MIPS) compared with a traditional approach. Laryngoscope. 2004;114:1945-8. 

2. Musch DC, et. al. The collaborative initial glaucoma treatment study: study design, methods, and baseline characteristics of enrolled patients. Ophthalmology. 1991;106:653-62. 

3. Sullivan LJ, O'Day J, McNeill P. Visual outcomes of pituitary adenoma surgery. J Clin Neuroophthalmol. 1991;1:262-7. 

4. Marcus M, Vitale S, Calvert PC, Miller NR.  Visual parameters in patients with pituitary adenoma before and after transsphenoidal surgery. Aust. N Z J Ophthalmol. 1991;19:111-8. 

5. Powell M. Recovery of vision following transsphenoidal surgery for pituitary adenomas. Br J Neurosurg. 1995:9:367-73.