Atypical pituitary abscess lacking rim enhancement and diffusion restriction with an unusual organism, Moraxella catarrhalis: A case report and review of the literature

BACKGROUND: Pituitary abscess (PA) can be fatal if diagnosed late. Rim enhancement is a typical radiological finding of PA on postgadolinium T1-weighted magnetic resonance imaging (MRI). Diffusion-weighted imaging is helpful in distinguishing PA from other sellar cystic lesions. Herein, we report the first atypical case of PA showing neither rim enhancement nor diffusion restriction with an unusual organism, Moraxella catarrhalis. CASE DESCRIPTION: A 77-year-old woman presented with headache, polyuria, polydipsia, and fatigue for a month before presenting to a local hospital. MRI showed pituitary enlargement with contrast enhancement. She had neither fever nor visual deficits and was followed up with hormonal replacement. Six months later, she complained of visual impairment, and MRI showed further pituitary enlargement with a thickened stalk compressing the optic chiasma. Neither rim enhancement nor diffusion restriction was observed. Endoscopic endonasal transsphenoidal surgery was performed based on the radiological diagnosis of lymphocytic hypophysitis or pituitary tumors. A thick, creamy yellow pus was drained from the sellar lesion. Intraoperative rapid histopathological findings revealed polymorphonuclear leukocytes infiltrating the pituitary gland. PA was diagnosed, and irrigation and open drainage of the abscess was performed. Bacterial culture of the pus detected M. catarrhalis by mass spectrometer, confirming the diagnosis. She underwent appropriate antibiotic administration, and her visual deficits improved. CONCLUSION: We report the first atypical case of PA showing neither rim enhancement nor diffusion restriction with M. catarrhalis. Even if preoperative findings are not suggestive of PA, it should be considered as a differential diagnosis. Intraoperative rapid histopathological findings are useful for accurately diagnosing PA and initiating appropriate surgical treatment.