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most sensitive for detecting any hemorrhagic components, which appear as areas of signal loss.solid components demonstrate moderate to bright enhancement.larger lesions are often heterogeneous and vary in signal due to areas of cystic change/necrosis/hemorrhage.Overall signal characteristics can significantly vary depending on tumor components such as hemorrhage, cystic transformation, or necrosis. It is able to delineate the mass exquisitely as well as clearly visualize the optic chiasm, anterior cerebral vessels, and cavernous sinuses.
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Solid adenomas without hemorrhage, typically have attenuation similar to the brain (30-40 HU) and demonstrate moderate contrast enhancement less marked than one typically sees in meningiomas. Calcification is rare. Non-contrast attenuation can vary depending on hemorrhagic, cystic, and necrotic components. Bilateral indentation by the diaphragma sellae as the tumor passes superiorly can give a snowman or figure-eight configuration 10.īecause these tumors are typically slow-growing, the pituitary fossa is almost invariably enlarged with thinned remodeled bone. Pituitary macroadenomas are by definition >10 mm diameter masses arising from the pituitary gland, and usually extending superiorly into the suprasellar cistern where it can compress the chiasm. They are a type of benign epithelial tumor composed of adenohypophyseal cells Radiographic features Most macroadenomas are non-secretory (endocrinologically inactive). Likelihood of surgical/histological invasion can be estimated with the Knosp classification. The oculomotor nerve (CN III) is most commonly involved, followed by the abducens nerve (CN VI) 10. They may compress cranial nerves resulting in deficits, although this is uncommon, seen in only 1-14% of cases 10.
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Once in the sinus, these tumors are difficult to resect completely. Prolactin-secreting tumors are most frequently responsible for cavernous sinus extension, and typically prolactin levels increase significantly when the tumor gains access to the sinus 10. Some macroadenomas demonstrate invasive growth, and extension into the cavernous sinuses is characteristic. In cases of prefixed or postfixed chiasms, or when the macroadenoma grows asymmetrically, then the optic nerves or optic tracts can be compressed, resulting in a variety of visual deficits. Patients typically complain of bumping into things or having car accidents, but as the macular fibers are often spared, they may not be aware of their visual deficits. This central part carries fibers from the nasal retina, and thus results in the classical bitemporal hemianopia 10. A prefixed optic chiasm is located anterior to its normal position over the tuberculum sellae, whereas a postfixed chiasm is located over the dorsum sellae 10.Ī macroadenoma growing superiorly out of the pituitary fossa (or for that matter other pituitary region masses) will contact, elevate and compress the central part of the chiasm in most individuals. The rest is divided between pre and postfixed chiasms. The optic chiasm is located directly over the pituitary gland in 80% of individuals. Rarely pituitary apoplexy may present acutely and often catastrophically. This mode of presentation is discussed in the article on pituitary microadenomas. Hormonal imbalance due to overproduction tends to present earlier and tumors are thus usually small at presentation. Some may present due to hormonal imbalance, with symptoms of hypopituitarism (from compression) or secretion. Patients typically present with symptoms of local mass effect on adjacent structures (especially optic chiasm).