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'Leave me alone' lesions of the petrous apex
K R Moore1, H R Harnsberger, C Shelton
1Department of Radiology, University of Utah School of Medicine and the Salt Lake Veterans Administration Medical Center, Salt Lake City, USA.
Purpose:
When troublesome MR imaging findings are noted in the petrous apex, the radiologist must determine if the area in question needs surgical therapy. Two nonsurgical entities, asymmetric fatty marrow and fluid-filled petrous air cells (trapped fluid), can be noted on conventional brain MR images and confused with pathologic lesions. Our observation that radiologists do not always confidently define the nonsurgical petrous apex lesions precipitated this investigation.
Methods:
Twenty-three patients with either asymmetric fatty marrow (six) or unilateral effusion in a pneumatized petrous apex (17) on MR images were studied. Eighteen patients underwent high-resolution temporal bone CT. For all patients, the medical charts were reviewed retrospectively and/or the surgical and clinical follow-up findings were reviewed with the referring physician.
Results:
In the patients with asymmetric fatty marrow, MR signal intensity followed fat on all sequences. The questioned apex in the patients with trapped fluid showed mixed MR signal characteristics (low to high T1 signal, high T2 signal). CT scans confirmed nonexpansile air-cell opacification.
Conclusion:
Asymmetric fatty marrow in the petrous apex and petrous air-cell effusions have characteristic MR and CT features that facilitate their correct diagnosis. Effusions 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.
Insights
Asymmetric fatty marrow and fluid in petrous apex air cells are common MR imaging findings that can mimic pathology. Characteristic MR and CT features help radiologists confidently diagnose these nonsurgical conditions.
Area of Science:
- Radiology
- Neuroimaging
- Otology
Background:
- Petrous apex lesions on MR imaging can be challenging to differentiate from non-pathologic findings.
- Asymmetric fatty marrow and fluid-filled petrous air cells are common mimickers of pathology.
- Accurate diagnosis is crucial to avoid unnecessary surgical intervention.
Purpose of the Study:
- To identify characteristic MR and CT imaging features of asymmetric fatty marrow and fluid-filled petrous air cells.
- To aid radiologists in confidently distinguishing these nonsurgical entities from pathologic lesions in the petrous apex.
Main Methods:
- Retrospective review of 23 patients with MR imaging findings suspicious for petrous apex lesions.
- Analysis of asymmetric fatty marrow (6 patients) and unilateral petrous air cell effusions (17 patients).
- High-resolution temporal bone CT in 18 patients; review of medical charts and clinical follow-up.
Main Results:
- Asymmetric fatty marrow demonstrated fat-suppressible signal intensity on all MR sequences.
- Fluid-filled petrous air cells (trapped fluid) showed mixed MR signal characteristics (low to high T1, high T2).
- CT confirmed nonexpansile air-cell opacification in cases of trapped fluid.
Conclusions:
- Asymmetric fatty marrow and petrous air-cell effusions possess distinct MR and CT features for accurate diagnosis.
- Effusions with intermediate/high T1 signal are often mistaken for cholesterol granulomas.
- Long-term CT follow-up can confirm the stability of effusions, aiding in diagnosis.