PITUITARY TUMORS THAT PRESENT AS SKULL BASE AND EXTRACRANIAL HEAD AND NECK MASSES

ANTHONY A. MANCUSO

KEY POINTS

Invasive pituitary adenoma can extensively invade the central skull base and mimic malignancy.
When there is an extensive lesion of the central skull base present, it should be determined whether it is separate from the pituitary gland, involving it, or possibly arising from the gland.
Developmental anomalies of the pituitary anlage can rarely present as nasopharyngeal and sphenoid sinus masses.

ECTOPIC PITUITARY TISSUE, ADENOMAS, AND ECTOPIC CRANIOPHARYNGIOMA

The anterior lobe of the pituitary develops from the Rathke pouch, which is an invagination of endoderm of the primordial nasopharynx.¹ Residual cells along the path of migration can result in functioning glandular tissue or abnormal masses anywhere from the nasopharynx to the suprasellar cistern. Related cysts or functioning pituitary glands in the nasopharynx are normally asymptomatic and about 1 × 1 cm in size.²^,³ They are located in the mucoperiosteum of the roof of the nasopharynx, usually about where the vomer lies against the base of the sphenoid bone.⁴^,⁵ Pituitary adenomas presenting in the nasopharynx are usually downward extensions of lesions arising in the pituitary fossa. Rarely, they come from Rathke pouch remnants.¹ Nasopharyngeal or sphenoid craniopharyngiomas have the same tendencies.

INVASIVE PITUITARY ADENOMAS

Invasive pituitary adenomas, for our purposes here, are those that can grow well beyond the limits of the sella and occasionally invade the nasopharynx, ethmoids, and even the nasal cavity. Some might also include those that just extend to the cavernous sinus in this group, but those lesions are relatively self-evident and are more in the realm of intracranial aspects of neuroradiology. The more extensive invasive pituitary adenomas that can involve virtually the entire central skull base (Figs. 32.1 and 32.2) produce findings relevant to clinical decision making for the head and neck imager.⁶^–⁸ It is extraordinarily important to correctly interpret invasive pituitary adenoma as such and not as a tumor of some other source. Such correct analysis leads to appropriate therapy as opposed to attempts at definitive extensive skull base surgery; the latter is not the correct approach to treatment of invasive pituitary adenomas.

FIGURE 32.1. Magnetic resonance study of a patient with invasive pituitary adenoma. A: T1-weighted (T1W) non–contrast-enhanced coronal image shows the mass (arrows) to encase the carotid artery in the cavernous sinus bilaterally and extend out into the central skull base inferiorly and laterally (arrows). Note that the nasopharynx is normal. B: T1W non–contrast-enhanced sagittal image shows the mass to replace the clivus and central skull base and fill the sphenoid sinus. The pituitary gland is not visualized as separate from the mass (arrow). C: T2-weighted image for comparison to (A) shows the mass to be generally brighter than brain and multiseptated. D: Contrast-enhanced T1W image shows diffuse fairly extensive enhancement and again the extent of the mass to be as described in (A) and inseparable from the pituitary gland.

FIGURE 32.2. Contrast-enhanced computed tomography (CECT) and magnetic resonance imaging study in another patient with invasive pituitary adenoma. A: CECT study showing the mass extending well into the central skull base and into the soft tissues below the skull base including the parapharyngeal and masticator spaces (arrows). Nasopharynx is also involved (arrowhead), but this was a submucosal mass on physical examination. B: Bone windows of the computed tomography study showing an expansile-appearing process in the central skull base and petrous apices (arrows) illustrating the chronic although aggressive nature of the mass. The extension into the soft tissues, including the nasopharynx and parapharyngeal space, is demonstrated again (arrowheads). C: T1-weighted (T1W) coronal image shows the mass centered in the central skull base and pituitary fossa encasing both carotid arteries with considerable suprasellar extension. D: T1W contrast-enhanced sagittal image showing that the mass cannot be separated from the pituitary gland. E: T1W axial image showing the extensive infiltrating mass that is in some areas slightly hypointense to brain. F: Contrast-enhanced T1W image showing that the mass is somewhat less intensely enhancing than the lesion seen in Figure 32.1. G: T2-weighted image again to contrast with the invasive pituitary adenoma in Figure 32.1A, showing this lesion to be slightly less intense than brain.