How Should a Nonfunctioning Pituitary Macroadenoma be Monitored After Debulking Surgery?

Yona Greenman; Naftali Stern

Disclosures

Clin Endocrinol. 2009;70(6):829-832. 

In This Article

Early Postoperative Assessment

Visual Fields

Resolution of headaches and amelioration of visual field defects occur shortly after surgery in the majority of patients. The recovery of visual fields is progressive, with an early fast phase of improvement during the first week after surgery, an early slow phase (4-6 months postoperatively) by the end of which most of the eventual recovery takes place and a late phase (up to 3-5 years) in which mild further improvement may still occur.[2] Overall, normalization of visual function occurs in 35-39% and improvement in 50-60% of patients.[2,3] Worsening of vision is reported in 0·5-2·4% of patients, and as with other surgical complications, its prevalence depends on the experience of the neurosurgeon and the volume of operations performed in a particular centre.[4] Based on these data, a neuroophthalmological assessment should be performed 1 week and again after 3-6 months following surgery. The visual status obtained in these evaluations will be the baseline for subsequent comparisons.

Pituitary Function

In most[5] but not all[6] series, normalization of one or more hypothalamo-pituitary-axis function has been reported after surgery, whereas worsening of pituitary function is less common. The degree of improvement is variable, occurring in 15-50% of patients.[5] This variability probably reflects the actual degree and duration of the preoperative impairment, surgical expertise, the use of different endocrine tests and criteria for the diagnosis of hypopituitarism as well as the surgical route of operation. Pituitary function normalized in 19·6%, improved in 30·1%, remained unchanged in 48·9% and worsened in 1·4% of patients following surgery by the transsphenoidal route; whereas after transcranial surgery, none of the patients had normalization, only 11·3% had improvement and 15% had deterioration of pituitary function, as reported by Nomikos et al.[7] Transient diabetes insipidus (DI) complicates up to 15% of surgeries, but permanent DI is less frequent, occurring in 0·9%[8] to 2% of patients. Transient hyponatremia secondary to ADH excess may occur in the context of a triphasic pattern of DI or as an isolated event, peaking at postoperative day 7.[9]

During the immediate postoperative period (7-10 days), emphasis should focus on evaluation and correction of corticotroph and posterior pituitary deficits. The recovery of the hypothalamo-pituitary adrenal-axis occurs very early in the postoperative period, as ACTH levels increase within hours after surgery in patients who recover adrenal function,[10] and an insulin tolerance test (ITT) performed within 8 days after surgery was 100% sensitive and specific in predicting long-term normalcy of the axis.[11] In practice, morning serum cortisol levels are measured 3-7 days after surgery depending on the schedule of perioperative glucocorticoid coverage, and indicate the need for continuing steroid replacement until definitive testing is performed. Thus, morning cortisol levels less than 100 nmol/l or over 450 nmol/l are consistent with ACTH deficiency and sufficiency, respectively, and intermediate levels require further testing.[12] ACTH stimulation tests, while easier and safer than ITT, are not a reliable enough means to detect new onset of postoperative secondary hypoadrenalism in the first 4-6 weeks, as adrenal cortical mass and response may be still preserved during this time interval, but the low-dose 1 μg ACTH test is a powerful and sensitive tool thereafter.[13] The time frame for recovery of other hypothalamo-pituitary-axes has not been longitudinally studied and the best timing for testing has not been established. Although this is traditionally performed 4-6 weeks after surgery,[9] the long-term predictive value of tests conducted at this time is not known. It is reasonable to re-assess the function of axes found to be impaired at the first postoperative evaluation 3, 6 and 12 months thereafter, both to assess the current status of pituitary function and need for hormone replacement, and to establish the baseline for subsequent follow-up.

Imaging

Early postoperative magnetic resonance images (MRI) are difficult to interpret owing to intrasellar fluid and blood collection, the presence of implanted sealing materials and incomplete descent of residual suprasellar tumour remnants. Therefore, the completeness of tumour resection and assessment of remnant size are better achieved by MRI performed at least 3-4 months after surgery.[14] In some cases, even at this point, the distinction between adenomatous tissue and postoperative changes and fibrosis may be difficult. In this context, 11C-methionine PET, which detects protein synthesis in viable tissue, could be helpful, but its place in the management of pituitary tumours needs further validation.[15] The initial postoperative MRI will be the baseline against which subsequent imaging will be compared with for the detection of recurrence or tumour progression.

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