Non-functional Pituitary Adenoma Detected on 18F-fluorodeoxyglucose Positron Emission Tomography (18F-FDG-PET) in a Patient with Mucosa-associated Lymphoid Tissue Lymphoma

Magnetic resonance imaging (MRI) is the modality of choice for the detection and characterization of a pituitary adenoma. Uptake of 18F-fluorodeoxyglucose (FDG) by intrasellar tumors, including pituitary adenomas, has been reported in several previous studies. We report a case where a pituitary adenoma was detected on FDG-positron emission tomography(PET), but the tumor was not detected with the use of sellar MRI. A 31-year-old woman was referred to the clinic due to a focal increase of FDG uptake at the pituitary fossa seen on whole body FDG-PET. The patient was receiving chemotherapy due to a recurred B-cell lymphoma of the mucosa-associated lymphoid tissue type. Subsequently, sellar MRI was performed, and images showed a small non-enhancing heterogenous cystic lesion in the midline of the pituitary gland, radiologically suggestive of a Rathke`s cleft cyst. However, sellar MRI failed to identify a lesion consistent with a pituitary tumor that corresponded to the site of increased FDG uptake detected by the use of PET, despite the inclusion of a dynamic contrast enhanced sequence. Despite the negative findings of the MRI examination, basal and stimulated levels of the GnRH free α-subunit were profoundly increased. Therefore, we suspected the presence of a non-functional pituitary tumor in addition to a Rathke`s cleft cyst, rather than pituitary involvement of a lymphoma, based on the hormone levels and PET scan findings.ope