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Segmental Imaging of the Trochlear Nerve: Anatomic and Pathologic Considerations
Nivedita Agarwal1, Ali Karim Ahmed, Richard H Wiggins
1Section of Radiology (Nivedita Agarwal), Hospital Santa Maria del Carmine, Rovereto, Italy ; Division of Neuroradiology (Nivedita Agarwal, RHW), Department of Radiology. University of Utah, Salt Lake City, Utah; Department of Neurosurgery (AKA, GLG), the Johns Hopkins School of Medicine, Baltimore, Maryland; Division of Neuro-ophthalmology (TJM), Department of Ophthalmology, the Johns Hopkins School of Medicine, Baltimore, Maryland; Division of Neuroradiology (MK), Department of Diagnostic Radiology, Rush University Medical Center, Chicago, Illinois; Department of Neuroradiology (LLM), Cedimagem/Alliar Diagnostic Center, Juiz de Fora, Brazil; Department of Radiology (AFC), Le Bonheur Children's Hospital, the University of Tennessee Health Sciences Center, Memphis, Tennessee; Department of Opththalmology (LCD), St. Jude Children's Research Hospital, Memphis, Tennessee; Department of Otolaryngology Head and Neck Surgery (MI), the Johns Hopkins School of Medicine, Baltimore, Maryland; Division of Neuroradiology (Nafi Aygun), Department of Radiology, the Johns Hopkins School of Medicine, Baltimore, Maryland; and Division of Neuroradiology (AMB), Department of Radiology, University Hospitals, Case Western Reserve University School of Medicine, Cleveland, Ohio.
Background:
The trochlear nerve (the fourth cranial nerve) is the only cranial nerve that arises from the dorsal aspect of the midbrain. The nerve has a lengthy course making it highly susceptible to injury. It is also the smallest cranial nerve and is often difficult to identify on neuroimaging.
Evidence Acquisition:
High-resolution 3-dimensional skull base MRI allows for submillimeter isotropic acquisition and is optimal for cranial nerve evaluation. In this text, the detailed anatomy of the fourth cranial nerve applicable to imaging will be reviewed.
Results:
Detailed anatomic knowledge of each segment of the trochlear nerve is necessary in patients with trochlear nerve palsy. A systematic approach to identification and assessment of each trochlear nerve segment is essential. Pathologic cases are provided for each segment.
Conclusions:
A segmental approach to high-resolution 3-dimensional MRI for the study of the trochlear nerve is suggested.
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