LEAVE ME ALONE LESIONS OF THE PETROUS APEX

PURPOSE: When troublesome MR imaging findings are noted in the petrous apex, the radiologist must determine if the area in question needs su rgical therapy. Two nonsurgical entities, asymmetric fatty marrow and fluid-filled petrous air cells (trapped fluid), can be noted on conven tional brain MR images and confused with pathologic lesions. Our obser vation that radiologists do not always confidently define the nonsurgi cal petrous apex lesions precipitated this investigation. METHODS: Twe nty-three patients with either asymmetric fatty marrow (six) or unilat eral effusion in a pneumatized petrous apex (17) on MR images were stu died, Eighteen patients underwent high-resolution temporal bone CT, Fo r all patients, the medical charts were reviewed retrospectively and/o r the surgical and clinical follow-up findings were reviewed with the referring physician. RESULTS: In the patients with asymmetric fatty ma rrow, MR signal intensity followed fat on all sequences. The questione d apex in the patients with trapped fluid showed mixed MR signal chara cteristics (low to high T1 signal, high T2 signal). CT scans confirmed nonexpansile air-cell opacification. CONCLUSION: Asymmetric fatty mar row in the petrous apex and petrous air-cell effusions have characteri stic MR and CT features that facilitate their correct diagnosis. Effus ions with intermediate or high T1 signal are most frequently confused with cholesterol granulomas. In those patients, long-term CT follow-up may be helpful to confirm their stability.