A radiologic score to distinguish autoimmune hypophysitis from nonsecreting pituitary adenoma preoperatively

Abstract

Background and purpose: Autoimmune hypophysitis (AH) mimics the more common nonsecreting pituitary adenomas and can be diagnosed with certainty only histologically. Approximately 40% of patients with AH are still misdiagnosed as having pituitary macroadenoma and undergo unnecessary surgery. MR imaging is currently the best noninvasive diagnostic tool to differentiate AH from nonsecreting adenomas, though no single radiologic sign is diagnostically accurate. The purpose of this study was to develop a scoring system that summarizes numerous MR imaging signs to increase the probability of diagnosing AH before surgery.

Materials and methods: This was a case-control study of 402 patients, which compared the presurgical pituitary MR imaging features of patients with nonsecreting pituitary adenoma and controls with AH. MR images were compared on the basis of 16 morphologic features besides sex, age, and relation to pregnancy.

Results: Only 2 of the 19 proposed features tested lacked prognostic value. When the other 17 predictors were analyzed jointly in a multiple logistic regression model, 8 (relation to pregnancy, pituitary mass volume and symmetry, signal intensity and signal intensity homogeneity after gadolinium administration, posterior pituitary bright spot presence, stalk size, and mucosal swelling) remained significant predictors of a correct classification. The diagnostic score had a global performance of 0.9917 and correctly classified 97% of the patients, with a sensitivity of 92%, a specificity of 99%, a positive predictive value of 97%, and a negative predictive value of 97% for the diagnosis of AH.

Conclusions: This new radiologic score could be integrated into the management of patients with AH, who derive greater benefit from medical as opposed to surgical treatment.

Fig 1.

Gadolinium-enhanced coronal (A) and sagittal (B) T1-weighted MR images, sellar sections, in a patient with AH. A, A perfectly symmetrically enlarged and homogeneously enhancing gland. Note that the enhancement is stronger than that of the adjacent cavernous sinuses (arrows). B, Grossly enlarged and avidly enhancing pituitary stalk that exerts a mass effect on the hypothalamus. Note the generalized mucosal thickening in the sphenoid sinus.

Fig 2.

A, Kernel attenuation estimate of the age distribution in patients with AH (dashed line) or nonsecreting pituitary adenoma (continuous line). B, Boxplots show the distribution of pituitary volume in patients with hypophysitis or adenoma. Each box represents the middle half of the distribution (interquartile range) and contains a solid line to indicate the median. The top (and bottom) whisker line extends from the 75th (and 25th) percentile to a calculated value corresponding to 1.5 times the interquartile range. The points outside the ends of the whiskers indicate outliers.

Fig 3.

A, Kernel attenuation estimate of the score distribution in patients with AH (dashed line) or nonsecreting pituitary adenoma (continuous line). B, ROC curve shows sensitivity (Sens.) and 1-specificity (Spec.) obtained by using each value of the score (from −13 to +8) as a possible classification cut-point for the diagnosis. The best cut-point is 1, which classifies correctly 97.26% of the patients. The AUC, representing the overall performance of the score, is 0.9917. C, Dotplot shows the distribution of the score in suspected AH, biopsy-proved lymphocytic hypophysitis (LH), biopsy-proved granulomatous hypophysitis (GH), and nonsecreting pituitary adenoma.