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The trochlear nerve: microanatomic and endoscopic study

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Abstract

The purpose of the present study was to analyze the relationships of the trochlear nerve with the surrounding structures through both endoscopic and microscopic perspectives. The aim was to assess the anatomy of the nerve and to carry out a thorough description of its entire course. A comprehensive anatomically and clinically oriented classification of its different segments is proposed. Forty human cadaveric fixed heads (20 specimens) were used for the dissection. The arterial and venous systems were injected with red and blue colored latex, respectively, in the transcranial dissection. For illustrative purposes, the arterial vessels were injected alone in endoscopic endonasal procedures. A CT scan was carried out on every head. Median supracerebellar infratentorial, subtemporal, fronto-temporo-orbito-zygomatic, and endoscopic endonasal transsphenoidal approaches were performed to expose the entire pathway of the nerve. A navigation system was used during the dissection process to perform the measurements and postoperatively to reconstruct, using dedicated software, a three-dimensional model of the different segments of the nerve. The trochlear nerve was divided into five segments: cisternal, tentorial, cavernous, fissural, and orbital. Detailed and comprehensive examination of the basic anatomical relationships through the view of transcranial, endoscope-assisted, and pure endoscopic endonasal approaches was achieved. As a result of a thorough study of its intra- and extradural pathways, an anatomic-, surgically, and clinically based classification of the trochlear nerve is proposed. Precise knowledge of the involved surgical anatomy is essential to safely access the supracerebellar region, middle fossa, parasellar area, and orbit.

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Acknowledgments

The present paper has been partially supported by the Maratò TV3 Grant 11/04/2011 Project [411/U/2011—Title: Quantitative analysis and computer aided simulation of minimally invasive approaches for intacranial vascular lesions.]

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Authors and Affiliations

  1. Department of Neurological Sciences, Division of Neurosurgery, Università degli Studi di Napoli Federico II, Naples, Italy

    Giorgio Iaconetta, Luigi Maria Cavallo & Paolo Cappabianca

  2. Department of Neurosurgery, Hospital Clinic, Faculty of Medicine, Universitat de Barcelona, C/de Villarroel 170, 08036, Barcelona, Spain

    Matteo de Notaris

  3. Department of Human Anatomy and Embryology, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain

    Matteo de Notaris, Arnau Benet, Jordina Rincon & Alberto Prats-Galino

  4. Division of Neurosurgery, International Neuroscience Institute, Hannover, Germany

    Madjid Samii

Authors
  1. Giorgio Iaconetta
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  2. Matteo de Notaris
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  3. Arnau Benet
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  4. Jordina Rincon
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  5. Luigi Maria Cavallo
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  6. Alberto Prats-Galino
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  7. Madjid Samii
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  8. Paolo Cappabianca
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Correspondence to Matteo de Notaris.

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Comments

Michael R. Gaab, Hannover, Germany

This is an excellent paper in competent anatomical and neurosurgical cooperation by a group of respected authors, who are already well known from previous skillful articles, e.g., on endoscopic transclival and retrosigmoid approaches, on the sphenopetroclival venous anatomy, and on similar microanatomical and endoscopical studies with preparation of the oculomotor and abducens nerves. Such basic anatomical articles which show the different surgical approaches and its (micro-) anatomic characteristics combining the microsurgical, endoscopic, and endoscope-assisted perspectives are of great value for the clinical neurosurgeon, who gets an anatomical guideline by this article for the preparation of the whole trochlear nerve in the skull base using microscopic and endoscopic views with details of the vascular and nerval structures. For a safe approach to deep seated, conventionally often “hidden” areas with the endoscope, the exact anatomical landmarks which guide our clinical dissection must be known. These are nicely presented here in endoscopic views using a significant number of well dissected cadavers with prefect vascular injections showing the key structures as will be seen in the patients under the microscope and endoscope. The authors systematically and convincingly divide the course of the N. trochlearis into five segments, from cisternal via tentorial, cavernous, and fissural to the orbital course of the nerve and present its characteristic structures after skillful anatomical preparation in seven informative combined microscopic and endoscopic illustrations using straight and angulated rigid endoscopes, and with exact anatomical measurements. So this article will help to expand the actual limits of “micro-invasive” microscopic and endoscopic approaches in these areas, and might be used as a guideline and preparation for the individual clinical situation. This article is therefore another example for the importance of the cooperation of endoscopically experienced neurosurgeons and of skillful neuroanatomists using representative anatomical specimens with vascular injections in order to familiarize the clinical neurosurgeon with the anatomy and the landmarks applicable to its clinical situation. Such systematic anatomical preparations presented in the view of the surgical approach will improve the safety or our patients undergoing surgery in these areas, and we may certainly expect further valuable similar articles from this distinguished group.

Stefan Linsler and Joachim Oertel, Homburg/Saar, Germany

Iaconetta et al. present a thorrough manuscript on the surgical anatomy of the trochlear nerve. They describe in detail its course from the midbrain to the orbit. Particular attention is given to the various surgical approaches with application of the endoscope.

Nowadays, shear endoscopic surgery in skull base lesions or endoscopic assisted skull base surgery is very common because of the technical developments of new endoscopes, HD cameras, and the required instruments over the last decades [1, 2]. Thus, the surgical approaches became more and more minimally invasive in the last years. The main benefits of this are the reduced trauma to the adjacent brain and nerve tissue on one side and the better view and illumination on the other side. While these advantages are evident, in our opinion the most significant disadvantage of the endoscopic approaches is that the preoperative preparation of the procedure, including surgical strategy, size and position of the craniotomy, determination of the ideal surgical corridor, etc., becomes more and more important. Having said this, it is easy to see why anatomical studies of various brain regions and approaches underwent a Renaissance during the last decades. Just to mention some, various profound studies on typical approaches to improve key hole surgery and to obtain better surgical results were performed [3, 4, 5, 6].

Iaconetta et al. review in meticulous detail the surgical anatomy of the trochlear nerve and its course from the view of the different suitable approaches. They describe the entire anatomical course of the trochlear nerve in the skull base und illustrate the microscopic cranial, the endoscope-assisted transcranial, and the endoscopic endonasal perspectives to assess the neurovascular and spatial relationships of the trochlear nerve to the adjacent anatomical structures of the skull base. Finally, they discuss different approaches in clinical use and their pitfalls.

We think that this study is very important because the trochlear nerve is at risk in many approaches [7, 8]. The nerve is small, and the diplopia caused by a nerve lesion frequently is considered to be a minor complication although the effect for the patient can be tremendous. Thus, every colleague who performs surgery in the area of the trochlear nerve should be aware of its course and the ideal strategies to avoid nerve lesioning. A precise knowledge of the surgical anatomy—as demonstrated in this study of the trochlear nerve—together with experience and training with the endoscope is essential to successfully perform minimal invasive neurosurgical procedures with the expected results. Regarding the use of the endoscope in skull base surgery, we believe that this manuscript is a valuable addition to the neurosurgical readers of Neurosurg Rev.

References

1. Grunert P, Gaab MR, Hellwig D, Oertel J (2009) Evolution of modern neuroendoscopy in Europe. Neurosurg Focus 27(3):E7

2. Kassam AB, Gardner P, Snyderman C, Mintz A, Carrau R (2005) Expanded endonasal approach: fully endoscopic, completely transnasal approach to the middle third of the clivus, petrous bone, middle cranial fossa and infratemporal fossa. Neurosurg Focus 19 (1):E6

3. Ammirati M, Musumeci A, Bernardo A, Bricolo A (2002) The microsurgical anatomy of the cisternal segment of the trochlear nerve, as seen through different neurosurgical operative windows. Acta Neurochir 144 (12): 1323–1327

4. Marinkovic S, Gibo H, Zelic O, Nikodijevic (1996) The neurovascular relationships and the blood supply of the trochlear nerve: surgical anatomy of its cisternal segemtn. Neurosurgery 38 (1):161–169

5. Rhoton AL, Jr. (2000) The posterior fossa cisterns. Neurosurgery 47 (3 Suppl):S287–297

6. Rhoton AL, Jr. (2002) The anterior and middle cranial base. Neurosurgery 51 (4 Suppl): S273–302

7. Oertel J, Gaab MR, Runge U, Schroeder HWS, Wagner W, Piek J (2004) Neuronavigation and complication rate in epilepsy surgery. Neurosurg Rev 27:214–217

8. Schroeder HWS, Oertel J, Gaab MR (2004) Endoscope-assisted microsurgical resection of epidermoids in the cerebellopontine angle. J Neurosurg 101:227–232

Henry W. S. Schroeder, Greifswald, Germany

Iaconetta et al. present a nice anatomical study of the course of the trochlear nerve using transcranial microscopic and endoscopic as well as endonasal endoscopic visualisation. They propose a five-segment classification of the trochlear nerve as a result of the study. This paper is a valuable addition to the literature. The high-quality images show clearly the course of the nerve in the various compartments. After reading this study, the reader has a thorough understanding of the anatomical, clinical, and surgical considerations of each nerve’s segment which will definitely help in performing a safe surgery.

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Iaconetta, G., de Notaris, M., Benet, A. et al. The trochlear nerve: microanatomic and endoscopic study. Neurosurg Rev 36, 227–238 (2013). https://doi.org/10.1007/s10143-012-0426-x

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