Analysis of indirect signs of microprolactinoma at MR imaging

Initial experience of 3 Tesla versus conventional field strength magnetic resonance imaging of small functioning pituitary tumours

BACKGROUND

Higher field strength magnetic resonance imaging (MRI) is becoming increasingly available and offers improved image quality; however, the clinical usefulness of this technique for the demonstration of surgically treatable functional pituitary adenomas has not been clearly established.

OBJECTIVE

To determine whether 3 Tesla (3T) MRI improves the detection of ACTH- and GH-secreting microadenomas over conventional imaging at field strengths of up to 1·5 Tesla (1·5T).

DESIGN

Data sets from postgadolinium T1-weighted MRI at 1·5T and 3T were blinded, randomly ordered and assessed for the presence of pituitary tumour by two radiologists. Where possible, lesion signal difference to noise ratio (SDNR) was calculated for quantitative comparison. Imaging diagnoses were correlated with subsequent surgical and histological findings.

PATIENTS

Twenty-four patients (10 men, 14 women) with biochemical evidence of Cushing's disease (19) or acromegaly (5) were identified over a 5-year period.

RESULTS

1·5T MRI gave a clear diagnosis of 12 pituitary tumours, all confirmed at 3T. Four additional definite lesions and one suspicious case were correctly identified at 3T. Histological correlation in 21 cases showed sensitivity improving from 54% with 1·5T to 85% with 3T. Radiologists' subjective image preference favoured 3T in 92%. Quantitative difference between tumour and parenchymal signal was significantly greater at 3T (mean SDNR -7·9 [3T] and -2·8 [1·5T], paired t-test P < 0·05).

CONCLUSIONS

3T MRI appears to offer increased conspicuity and detection of GH- and ACTH-secreting pituitary microadenomas. It is potentially clinically useful when 1·5T imaging is negative or equivocal.

11C-methionine PET for the diagnosis and management of recurrent pituitary adenomas

PURPOSE

The detection of recurrent pituitary adenoma by magnetic resonance imaging (MRI) is rendered uncertain by the tissue remodelling that follows surgery or radiotherapy. We aimed to evaluate the contribution of PET with 11C-methionine (MET-PET) in the detection and management of recurrent pituitary adenoma.

METHODS

Thirty-three patients with pituitary adenoma were evaluated postoperatively by MET-PET, either because of biological evidence of active residual tumour or because of MRI demonstration of non-functional adenoma growth. We studied 24 secreting adenomas and nine non-functional adenomas.

RESULTS

In 30 patients, MET-PET detected abnormally hypermetabolic tissue. In 14 out of these, MRI did not differentiate between residual tumour and scar formation. In nine of these 14 cases, major therapeutic decisions were undertaken (radiosurgery and surgery). In another group of 16 patients, both MET-PET and MRI detected abnormal tissue. In one case, neither MRI nor MET-PET detected adenomatous tissue. Finally, abnormal tissue was detected in two patients on MRI solely. In these two cases, failure of MET-PET to reveal the adenoma was attributable to concomitant inhibitory therapy. The sensitivity of MET-PET and MRI varied as a function of the tumour type: all non-functional adenomas were localised by both modalities, while MET-PET detected all adrenocorticotropic hormone-secreting adenomas whereas MRI depicted only one of these eight lesions. Fifteen out of 17 patients treated by radiosurgery showed clinical improvement after treatment.

CONCLUSION

We suggest that MET-PET is a sensitive technique complementary to MRI for the detection of residual or recurrent pituitary adenomas. It should gain a place in the efficient management of these tumours.

Effects of estrogen replacement therapy on pituitary size, prolactin and thyroid-stimulating hormone concentrations in menopausal women

There are few studies in the literature investigating pituitary size at an age consistent with the menopause and the influence of estrogen replacement therapy on pituitary height. We therefore evaluated the effect of estrogen on pituitary size, prolactin and thyroid-stimulating hormone (TSH) levels in menopausal women. Sixty-nine women were evaluated, 47 using estrogen and 22 controls. The measure of pituitary height was obtained from magnetic resonance imaging. Hormone evaluation did not show a statistically significant difference in mean (+/-standard deviation) prolactin level between the group using estrogen (7.6 +/- 6.4 ng/ml) and controls (5.1 +/- 3.4 ng/ml; p = 0.15), yet mean TSH level was significantly higher in the treated group (1.9 +/- 1.5 vs. 1.2 +/- 0.9 microU/ml; p = 0.03). Mean pituitary height in the estrogen-treated group (5.2 +/- 1.4 mm) was greater than in the controls (4.4 +/- 1.4 mm; p = 0.04). However, when such potential confounders as age, prolactin and TSH levels, treatment and duration of estrogen exposure were considered, the magnitude of difference did not attain significance. In conclusion, estrogen may play a role in pituitary size, since a mean difference in pituitary height, estimated as 0.78 mm, was detected between the groups in favor of the estrogen-treated group. This suggestion can be investigated in further studies.