From the Guidelines
Magnetic Resonance Imaging (MRI) with 3.0T is the best imaging study for evaluating the brainstem, as it provides superior signal-to-noise ratios, gradient strength, and spatial resolution compared to 1.5T imaging. The brainstem, including the midbrain, pons, and medulla oblongata, can be evaluated using specific MRI protocols, including thin-cut T1-weighted, T2-weighted, and contrast-enhanced T1-weighted sequences 1.
Some key points to consider when evaluating the brainstem with MRI include:
- The use of a phased-array head coil, which suffices for most examinations, although specialized surface coils may supplement examinations of peripherally located nerves 1
- The importance of thin-section imaging with high-spatial resolution to directly image the cranial nerves (CNs) or their course, with slice thickness calculated for optimal spatial resolution without introducing partial-volume effect 1
- The use of intravenous (IV) contrast, which is imperative for the evaluation of cranial neuropathy with MRI, including the brainstem 1
- The utility of diffusion-weighted imaging (DWI) in assessing for acute infarctions, cellular tumors, or specific lesions that may affect CN function, such as epidermoids or cholesteatomas 1
The brainstem segments, including the CN nuclei and fascicular nerve segments, are not well seen on MRI but can be deduced by recognizing surrounding anatomy and are best imaged with various T2-weighted, multi-echo, and fluid-attenuated inversion-recovery (FLAIR) sequences 1. Three-dimensional isotropic heavily T2-weighted sequences with low CSF artifact provide submillimeter high-spatial and contrast resolution to image the cisternal and dural cave segments of the CNs and can be reformatted into multiple planes 1.
Overall, MRI with 3.0T is the preferred imaging modality for evaluating the brainstem due to its superior spatial resolution and ability to detect subtle abnormalities.
From the Research
Imaging Studies for Evaluating Brainstem
- Magnetic Resonance Imaging (MRI) is considered a valuable tool for evaluating brainstem anatomy and pathology, as it provides high-resolution images of the brainstem structures 2, 3, 4.
- High-field MRI (7 Tesla) with diffusion tensor imaging (DTI) can provide detailed information about the cyto- and myeloarchitecture of the brainstem, allowing for precise determination of the extension and topography of brain lesions 2.
- A high-resolution interactive atlas of the human brainstem using MRI has been developed, which can be used for neuroanatomical education, research, and enhanced neurosurgical planning 3.
- Functional MRI (fMRI) of the brainstem is a relatively young field that is rapidly evolving, but it is still challenging due to technical limitations and physiological noise 5.
- MRI has been shown to be superior to computed tomography (CT) in detecting brainstem lesions, particularly in cases of ischemic stroke, and can provide valuable information about the extent and location of infarction 6.
Techniques and Considerations
- High-resolution structural MRI and DTI can be used to acquire detailed images of the brainstem, but require specialized equipment and techniques 2, 3.
- Manual segmentation and deterministic fiber tractography can be used to create detailed maps of brainstem structures and fiber bundles 3.
- Physiological noise and spatial resolution issues can be mitigated using appropriate sequences, coils, and spatial preprocessing techniques 5.
- The choice of imaging technique and protocol will depend on the specific clinical or research question being addressed, as well as the availability of equipment and expertise 4, 5.