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Chapter 14: Pituitary

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Which statement about pituitary microadenomas is true?

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(A) By definition, they are less than 1.0 cm in size.

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(B) They are best seen on coronal T2 gadolinium-enhanced magnetic resonance scans.

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(C) They are rarely found at autopsy in asymptomatic individuals.

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(D) Fifteen percent will enlarge to macroadenomas.

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(A) The “gold standard” for classifying pituitary adenomas is based on immunohistochemistry and electron microscopy. However, from a surgical standpoint, they can be classified by size and growth characteristics. In the simplest form, adenomas are divided into two groups: microadenomas (<10 mm in diameter) and macroadenomas (≥10 mm in diameter). To further classify macroadenomas, it can be useful to use a system that takes into account grade, degree, and direction of extrasellar extension (stage). Microadenomas of the pituitary are best visualized with a coronal T1 MRI. Eighty to 95% of such studies will show a focal hypointense lesion within an otherwise homogenous adenohypophysis. The excellent sensitivity of unenhanced T1-weighted spin echo (SE) MRI for microadenomas has made it the primary sequence for imaging the pituitary gland. Contrast is reserved for those cases in which there is good clinical or biochemical evidence of a pituitary adenoma with a negative or equivocal plain MRI. In most cases, the best imaging routine is to perform a plain scan followed by a repeat T1-weighted coronal sequence immediately after intravenous injection of contrast (gadolinium). Autopsy studies have repeatedly shown that 20–25% of the general population harbor small pituitary microadenomas. Microadenomas are usually clinically silent and occur in patients without apparent endocrine symptoms. Whereas very few microadenomas will show interval growth, more than one-third of macroadenomas will increase in size.

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BIBLIOGRAPHY

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Atlas S. Magnetic Resonance Imaging of the Brain and Spine, 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009.

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Jane J, Thapar K, Laws E. Pituitary tumors. In: Winn HR (ed.), Youmans Neurological Surgery, 6th ed. Philadelphia, PA: W. B. Saunders; 2011:1476–1510.

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A 19-year-old woman has had amenorrhea and galactorrhea for 13 months. Her prolactin level is 100 ng/mL (normal 4–23 ng/mL for nonpregnant women). She brought a recent magnetic resonance image (MRI) with her (see Fig. 14-1). After other causes of hyperprolactinemia have been ruled out, she should

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Image not available.

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FIGURE 14-1. Coronal magnetic resonance scan (T1 with contrast).

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(A) Begin medical therapy with dopamine agonists

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(B) Begin medical therapy with oral contraceptives

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(C) Begin calcium supplementation

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(D) Undergo transsphenoidal resection of the lesion

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(A) The MRI shown in Fig. 14-1 shows a microadenoma on the right side of the sella. Regardless of cause, the classic features of prolactin excess in women are galactorrhea and amenorrhea. In men, decreased libido and impotence are common. The elevated prolactin level, combined with the findings on MRI, makes prolactinoma a likely diagnosis. However, pituitary incidentalomas are very common, and other possible etiologies must be excluded. Other common causes of increased prolactin secretion include pregnancy, hypothalamic-pituitary disorders, primary hypothyroidism, and drug ingestion (estrogen therapy, oral contraceptives, dopamine antagonists, monoamine oxidase inhibitors [MAOIs], intravenous cimetidine, and verapamil). Other causes can include nipple stimulation, chest wall lesions, spinal cord lesions, chronic renal failure, or severe liver disease. Prolactin secretion from the pituitary is primarily under inhibitory control by dopamine, which is secreted by the hypothalamus. Increased production of prolactin will suppress luteinizing hormone (LH) and follicle-stimulating hormone (FSH) production, leading to decreased estrogen production. In the short term, these abnormalities can lead to galactorrhea and hypogonadism. In the long ...

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