<s>[INST] context: This patient has clinical features of a pituitary adenoma with acromegaly. Pituitary adenomas range from small lesions that do not enlarge the gland to expansive tumors that erode the sella turcica and impinge on adjacent cranial structures. Adenomas smaller than 10 mm in diameter are referred to as microadenomas, and larger ones are termed macroadenomas. Microadenomas do not produce symptoms unless they secrete hormones. The mass effects of pituitary macroadenomas include impingement on the optic chiasm, often with bitemporal hemianopsia and loss of central vision, oculomotor palsies when the tumor invades the cavernous sinuses, and severe headaches. Large adenomas may invade the hypothalamus and lead to loss of temperature regulation, hyperphagia, and hormonal syndromes because they interfere with the normal hypothalamic input to the pituitary. Symptoms of acromegaly include characteristic facial changes, goiter, barrel chest, abnormal glucose tolerance, male sexual dysfunction, menstrual disorders in women, degenerative arthritis, peripheral neuropathy, and thickened skin. The other choices represent tests that will not provide the diagnosis of pituitary tumor.Diagnosis: Acromegaly, pituitary adenoma [/INST] question: A 30-year-old woman complains of headache, visual disturbances, deepening of the voice, and generalized weakness. She reports amenorrhea for the past year and states that she recently required a larger shoe size. Laboratory studies show impaired glucose tolerance. What other procedure would be useful for establishing your diagnosis? | options: A: CBC with differential count B: CT scan of the abdomen C: MRI of the sella turcica D: Test for serum 21-hydroxylase | answer: C </s>