Nonfunctioning Pituitary Macroadenoma: General Points

Abstract

Nonfunctioning pituitary macroadenomas, also named nonsecreting adenomas, are frequently in fact gonadotropic adenomas, more rarely null-cell adenomas. They are responsible for neurologic symptoms (mainly visual field defect, headache) or endocrinologic symptoms (mainly anterior pituitary insufficiency). They are also very frequently discovered by chance and can be totally asymptomatic. In the latter case, a conservative approach can be proposed, particularly in the elderly, with a long-term MRI follow up. In young patients, finding a large, invasive pituitary adenoma—secreting or not—should prompt research of AIP and MEN1 gene mutations. Family history of pituitary adenomas or other features of the MEN1 syndrome in the patient and family should also be used to orient genetic research. In every case, a strict imaging protocol must be applied after surgery, the risk of recurrence being around 30 % Pituitary nonfunctioning macroadenomas are usually centered by an enlarged sella turcica. Signal intensity is usually inhomogeneous, particularly on T2W images with disseminated areas of hyperintensities reflecting cystic or necrotic components. T1 hyperintensity indicates the presence of blood, as does fluid-fluid level (Figs. 4.1 and 4.2). Old hemorrhage may be detected on T2*WI only (Fig. 4.3). Gadolinium injection offers a more clear-cut demonstration of tumoral contours; it enhances the normal pituitary tissue, which is distorted and displaced laterally on one side, and superiorly, but quite never inferiorly (Fig. 4.4). Demonstration of the normal residual pituitary gland is of crucial importance for the neurosurgeon. Enhancement of the dura, the so-called dural tail (Figs. 4.4 and 4.5), previously described as specific of meningiomas, has been described with large pituitary adenomas, especially if hemorrhagic or soon after surgery, and with perisellar aneurysms and other sellar tumors. The degree of enhancement of the solid part of the pituitary adenoma does not reflect the vascular density of the tumor and is thus not predictable of a potential perioperative hemorrhage. Conversely, flow-void linear images on T1WI or T2WI indicate the presence of intratumoral arteries (Fig. 4.6). Nonfunctioning macroadenomas present usually with an extrasellar extension, upward into the suprasellar cistern, downward into the sphenoid sinus, or laterally into the cavernous sinus. Upward extension is present in more than 70 % of cases. The suprasellar component of the largest macroadenomas is often multilobular (Fig. 4.7). The sellar diaphragm can operate as a belt, giving the adenoma an hourglass shape. If the suprasellar extension is moderate, the T1-hyperintense posterior lobe is compressed and flattened, and best identified in axial T1 fat-saturated noncontrast WI. Aberrant storage of antidiuretic hormone, the so-called ectopic posterior lobe, occurs when the pituitary stalk is severely compressed, i.e., in practice with macroadenomas more than 20 mm in height (see Chap. 53). Various degrees of distortion or thinning of the optic chiasm can be observed. Its hyperintensity on T2WIs could indicate a poor visual prognosis, but the lesion can be reversible if the responsible pituitary adenoma is quickly removed (Fig. 4.8). Ptosis of a V-shaped appearing optic chiasm within a secondary empty sella frequently occurs after surgery.