Trochlear nerve
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At the time the article was created Frank Gaillard had no recorded disclosures.
View Frank Gaillard's current disclosuresAt the time the article was last revised Rohit Sharma had no financial relationships to ineligible companies to disclose.
View Rohit Sharma's current disclosures- Trochlear nerve (CN IV)
- Trochlear nerve (IV)
- Fourth cranial nerve
- Cranial nerve 4
- Cranial nerve IV
- CN IV
- Nervus trochlearis
- Nervus cranialis IV
The trochlear nerve is the fourth (CN IV) and thinnest cranial nerve. It exits the midbrain posteriorly, eventually passes into the cavernous sinus and into the orbit where it supplies superior oblique muscle with motor fibres (TA: nervus trochlearis or nervus cranialis IV).
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Gross anatomy
Nucleus and intraparenchymal portion
The trochlear nucleus is located in the dorsoventral midbrain, ventral to the periaqueductal grey matter. Its fibres course dorsally and decussate dorsal to the periaqueductal grey matter before exiting the brainstem immediately below the inferior colliculus. It is the only cranial nerve to exit the brainstem posteriorly.
Cisternal portion
The nerve rounds the cerebral peduncles in the ambient cistern. Eventually, along with the oculomotor nerve (CN III), it courses anteriorly between the superior cerebellar artery below and posterior cerebral artery above before piercing the dura between the free and attached edge of tentorium cerebelli.
Cavernous sinus portion
Within the cavernous sinus, the trochlear nerve is located initially below the oculomotor nerve in the lateral wall of the sinus, although by the time it reaches the superior orbital fissure, it lies above it (outside the tendinous ring). It is the "Tarts" in this infamous mnemonic.
Orbital portion
It enters the orbit outside the tendinous ring, between the superior ophthalmic vein and the superolateral quadrant of the ring. Once in the orbit, it arches up and medially above the superior rectus and levator palpebrae superioris to innervate the superior oblique.
Radiographic features
MRI
Although the nerve is very thin, on high-resolution T2 weighted imaging (e.g. FIESTA/CISS) it can sometimes be visualised as a very thin structure. Dedicated higher-resolution sequences can also be performed if greater detail is required 5.
Related pathology
References
- 1. Chummy S. Sinnatamby. Last's Anatomy. (2011) ISBN: 9780702033957 - Google Books
- 2. Carmine D. Clemente. Anatomy. (2011) ISBN: 9781582558899 - Google Books
- 3. Sheth S, Branstetter B, Escott E. Appearance of Normal Cranial Nerves on Steady-State Free Precession MR Images. Radiographics. 2009;29(4):1045-55. doi:10.1148/rg.294085743 - Pubmed
- 4. R. Shane Tubbs. Nerves and Nerve Injuries. (2015) ISBN: 9780124103900 - Google Books
- 5. Choi B, Kim J, Jung C, Hwang J. High-Resolution 3D MR Imaging of the Trochlear Nerve. AJNR Am J Neuroradiol. 2010;31(6):1076-9. doi:10.3174/ajnr.A1992 - Pubmed
- 6. FIPAT. Terminologia Anatomica. 2nd Ed. FIPAT.library.dal.ca. Federative International Programme for Anatomical Terminology, 2019. https://fipat.library.dal.ca/TA2/
Incoming Links
- Ambient cistern
- Medical abbreviations and acronyms (I)
- Tuberculous meningitis
- Neurovascular compression syndromes
- Inferolateral trunk
- Superior cerebellar artery
- Extraocular muscle nerve supply (mnemonic)
- Basal vein of Rosenthal
- Orbital apex
- Cavernous sinus haemangioma
- Cranial nerve nuclei
- Superior oblique myokymia
- Orbital nerve supply
- Orbital apex syndrome
- Extraocular muscles
- Transition zone (nerve)
- Superior ophthalmic vein
- Trochlear nucleus
- Cranial nerves (mnemonic)
- Superior medullary velum
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