It was concluded that the patient had a non-functioning pituitary adenoma with essentially normal endocrine function (except for surgical athyreosis), and that surgery was not required and would increase the risk of hypopituitarism. Because of the large size and extension of the tumor, how- ever, therapeutic x ray was administered to the pituitary (4000 R over a 3- week period). This was well tolerated. Subsequent endocrinological studies have resulted in normal findings. The patient's visual fields have been tested regularly and have been normal. In 1977 her serum cortisol level was 9.9 and later 16 tg/100 ml, and in 1978 it was 19 w/100 ml (normal range 5-20), indicating normal pituitary function. In the past the patient has had regular pregnancies, having 14 children, the last one in 1968 at age 35. Though she still menstruates regularly, she has suffered from menorrhagia in the past few years, and an endometrial biopsy revealed proliferative endometrium and basalia. This may have influenced the lack of further pregnancies in recent years. Since there have been a number of reports of development of pituitary hypertrophy and tumor formation associated with hypothyroidism in animals (100-102) and human beings (103-106), this etiology must be considered. The only evidence of a hypothyroid state in this patient has been on those occa- sions when she was taken off thyroxin treatment in preparation for testing (Table 4). Since her thyroxin levels at those times were low or in the lownormal range, it appears that her pituitary was responding to thyroid de- ficiency and that the tumor was not autonomously responsible for the TSH elevations. The possibility that thyroid hypofunction led to the development of pituitary tumor in this case seems unlikely because long-standing hypothyroidism is usually required to produce such tumors, and this was not apparent in her case. Table 4. Year 1965 1967 19694 19726 1973 1974 Thyroid Hormone Levels in Pituitary Tumor Case. v, (ye/d1) TSH (wW/dl) Year 8.6 2.2 1.0 1.7 110.0 1975 1976¢ 1977 (Mar) 1977 (Sep) 1978 0.4 17.8 @Thyroidectomy. 1.0 Presurgical levels. bore T, Rx for testing. ‘Pituitary tumor discovered. Off Ty, for testing: - 51 - T, (ug /d1) 5.8 0.5 5.4 9.0 6.7 TSH (wW/d1) 5.9 115 3.8 5.6 1.8