The Rectus Capitis Lateralis and the Condylar Triangle: Important Landmarks in Posterior and Lateral Approaches to the Jugular Foramen

LABORATORY INVESTIGATION J Neurosurg 127:1398–1406, 2017

The rectus capitis lateralis and the condylar triangle: important landmarks in posterior and lateral approaches to the jugular foramen

Michael A. Cohen, MD,1,2 Alexander I. Evins, PhD,1 Gennaro Lapadula, MD,1,3 Leopold Arko, MD,1,4 Philip E. Stieg, PhD, MD,1 and Antonio Bernardo, MD1

1Department of Neurological Surgery, Weill Cornell Medical College, New York, New York; 2Department of Neurological Surgery, Rutgers New Jersey Medical School, Newark, New Jersey; 3Department of Neurology and Psychiatry, Neurosurgery, “Sapienza” University of Rome, Italy; and 4Department of Neurological Surgery, Temple University Medical School, Philadelphia, Pennsylvania

OBJECTIVE The rectus capitis lateralis (RCL) is a small posterior cervical muscle that originates from the transverse process of C-1 and inserts onto the jugular process of the occipital bone. The authors describe the RCL and its anatomical relationships, and discuss its utility as a surgical landmark for safe exposure of the jugular foramen in extended or combined skull base approaches. In addition, the condylar triangle is defined as a landmark for localizing the vertebral artery (VA) and occipital condyle. METHODS Four cadaveric heads (8 sides) were used to perform far-lateral, extended far-lateral, combined transmastoid infralabyrinthine transcervical, and combined far-lateral transmastoid infralabyrinthine transcervical approaches to the jugular foramen. On each side, the RCL was dissected, and its musculoskeletal, vascular, and neural relationships were examined. RESULTS The RCL lies directly posterior to the internal jugular vein—only separated by the carotid sheath and in some cases cranial nerve (CN) XI. The occipital artery travels between the RCL and the posterior belly of the digastric muscle, and the VA passes medially to the RCL as it exits the C-1 foramen transversarium and courses posteriorly toward its dural entrance. CNs IX–XI exit the jugular foramen directly anterior to the RCL. To provide a landmark for identification of the occipital condyle and the extradural VA without exposure of the suboccipital triangle, the authors propose and define a condylar triangle that is formed by the RCL anteriorly, the superior oblique posteriorly, and the occipital bone superiorly. CONCLUSIONS The RCL is an important surgical landmark that allows for early identification of the critical neurovascular structures when approaching the jugular foramen, especially in the presence of anatomically displacing tumors. The condylar triangle is a novel and useful landmark for identifying the terminal segment of the hypoglossal canal as well as the superior aspect of the VA at its exit from the C-1 foramen transversarium, without performing a far-lateral exposure. https://thejns.org/doi/abs/10.3171/2016.9.JNS16723 KEY WORDS rectus capitis lateralis; suboccipital triangle; jugular foramen; far lateral; muscle; anatomy

arge tumors of the jugular foramen with intracra- gical landmarks to avoid injury to the critical neurovascu- nial, intrapetrous, and/or extracranial extensions re- lar structures within. quire the use of extended or combined approaches The rectus capitis lateralis (RCL) muscle is a small deep thatL provide high cervical exposure necessary for manipu- muscle that connects the transverse process of C-1 (C1TP) lation of the internal jugular vein (IJV).4,9,13 The complex, with the jugular process of the occipital bone, assists in dense, and deep nature of the jugular foramen and upper anterior and lateral bending of the occiput in relation to the lateral cervical regions necessitates the use of precise sur- cervical spine, and plays a minor role in atlantooccipital

ABBREVIATIONS C1TP = C-1 transverse process; CN = cranial nerve; ICA = internal carotid artery; IJV = internal jugular vein; RCL = rectus capitis lateralis; VA = vertebral artery. SUBMITTED April 14, 2016. ACCEPTED September 15, 2016. INCLUDE WHEN CITING Published online January 27, 2017; DOI: 10.3171/2016.9.JNS16723.

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Unauthenticated | Downloaded 10/10/21 11:49 PM UTC The rectus capitis lateralis and condylar triangle stability (Fig. 1). The RCL, which lies anterior to the suboccipital triangle and centrally within the jugular foramen and high cervical regions, maintains a constant relationship with the structures exiting the jugular foramen, the IJV within the carotid sheath, and the facial nerve (cranial nerve [CN] VII) as it exits the stylomastoid foramen. We describe the RCL and its anatomical relationships, and discuss its utility as a surgical landmark for safe exposure of the jugular foramen and its contents in extended or combined skull base approaches. In addition, we define the condylar triangle—formed by the RCL anteriorly, the superior oblique posteriorly, and the occipital bone superiorly—as a landmark for localizing the vertebral artery (VA) and occipital condyle without far-lateral exposure. Methods Four preserved cadaveric heads (8 sides) underwent far-lateral, extended far-lateral, transmastoid transcervical, and combined far-lateral transmastoid transcervical approaches to the jugular foramen and the RCL, and its musculoskeletal, vascular, and neural relationships were examined (Figs. 2–4). On 2 of these sides, full anatomical dissections with complete exposure of the jugular foramen were performed (Figs. 5 and 6). FIG. 2. Surgical approaches to the jugular foramen and the RCL. The Far-Lateral and Extended Far-Lateral Approach RCL separates the far-lateral approach (blue) and the transcondylar and The jugular foramen was approached posteriorly using transtubercular variant (green) from the jugular foramen (purple) anteriorly. The transmastoid approach is depicted in orange.

the far-lateral and extended far-lateral approaches (Fig. 3). For the far-lateral approach, a horseshoe-shaped incision was made, and the superficial and middle muscle layers were dissected as a myocutaneous flap inferiorly and anteriorly until the mastoid tip was exposed.6 The suboccipital triangle was identified (Fig. 3A and B). The VA was local- ized in the suboccipital triangle, and the superior oblique was detached and reflected inferiorly (Fig. 3C).7 The myocutaneous flap was not reflected past the superior-anterior border of the RCL muscle, the location of the stylomastoid foramen. A lateral suboccipital craniectomy and C-1 lami- nectomy were performed. In the extended far-lateral approach, the posterior belly of the digastric muscle was detached from the digastric groove, and the occipital artery was freed and protected. The RCL was then identified under the digastric muscle and occipital artery.1,6 The anterior border of the RCL was dissected off the carotid sheath, and the muscle was detached from the jugular process. The jugular process was then removed in order to expose the jugular foramen. For the purposes of this study, we considered the conventional far-lateral approach as limited by the posterior border of the RCL anterosuperiorly and the extended far- lateral approach as continuing anterior to the RCL into the FIG. 1. Illustration of the RCL. The RCL originates from the C1TP and carotid sheath. inserts on the jugular process of the occipital bone. The relationships between the RCL, IJV, occipital artery, and CN VII are depicted as well Combined Transmastoid Infralabyrinthine Transcervical as CNs IX–XI passing through the jugular foramen adjacent to the RCL. Approach The transverse and sigmoid sinuses are depicted as they descend to form the jugular bulb just superior to the RCL. Copyright Andy Rekito. The jugular foramen was approached laterally using Published with permission. the transmastoid transcervical approach. A C-shaped or

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labyrinthine mastoidectomy was performed, the sigmoid sinus was exposed, the mastoid antrum was opened, and the incus was identified (Fig. 4). The lateral and posterior semicircular canals were identified and skeletonized, and the presigmoid dura and endolymphatic sac were uncov- ered. The fallopian canal was skeletonized beginning inferiorly to the lateral semicircular canal and continued inferiorly to the stylomastoid foramen. The jugular process was exposed while maintaining control of CN VII, and the jugular bulb and IJV were completely skeletonized. The RCL was dissected off the carotid sheath anteriorly and detached from the jugular process superiorly, the jugular process was drilled, and the jugular foramen was exposed.

Combined Far-Lateral Transmastoid Infralabyrinthine Transcervical Approach The approaches described above were combined to provide exposure of the condylar fossa, jugular bulb within the mastoid, and IJV in the upper cervical region with complete access to the jugular foramen from posterior, lateral, and anterolateral perspectives (Fig. 4).

Detachment of the RCL and Exposure of the Jugular Process To expose the jugular process, the RCL had to be detached from its insertion site on the jugular process. To safely accomplish this, the posterior belly of the digastric muscle was first detached from the digastric groove and then reflected inferiorly and anteriorly to expose the jugular process and anterior border of the RCL. Care was taken to avoid injury to CN VII. At this stage, the occipital artery should be coagulated or preserved and reflected away from the RCL. With the suboccipital triangle exposed, the superior oblique muscle was detached and reflected anteriorly and inferiorly. The posterior wall of the carotid sheath was identified and dissected away from the RCL at the midportion of the muscle. Dissection in the space between the carotid sheath and RCL continued superiorly until reaching the jugular process. Again, care was taken to avoid injury to CN VII, which lies several millimeters anterior to the superior aspect of the RCL. Once the RCL was completely dissected off the carotid sheath, the mus- FIG. 3. The extended far-lateral approach and the condylar triangle cle was detached from the jugular process from anterior (CT). A and B: The suboccipital triangle (ST) is formed by the superior to posterior. The jugular process was then safely drilled to oblique (SO) and inferior oblique (IO) muscles and the rectus capitis expose the jugular foramen (Fig. 4 right). posterior major. The RCL is located just anterior to the SO and is observed as it originates from the C1TP and inserts on the jugular process medial to the mastoid tip. The CT is formed by the RCL, SO, and a line Quantitative Measurements connecting these muscles along the occipital bone. The intramuscular A 3.5-inch graduated Castroviejo caliper was used to segment of the occipital artery (OA) typically courses within the CT along measure the distances between the jugular process and the occipital bone. C: The CT is opened by reflecting the SO anteriorly C1TP, styloid process and the RCL, medial turn of the and inferiorly to expose the posterior aspect of the occipital condyle. DM VA and the RCL, cervical internal carotid artery (ICA) = digastric muscle; SC = splenius cervicis. and the RCL, CN VII at the stylomastoid foramen and the RCL, and CN IX in the carotid sheath and the RCL reverse S-shaped incision was placed at the asterion and on all 8 cadaveric sides. Distances between the RCL and extended down to the posterior border of the sternocleido- the styloid process, medial turn of the VA, cervical ICA, mastoid muscle. The mastoid was exposed, and the myo- and CN IX were obtained by measuring the distance be- cutaneous flap was reflected anteriorly. Upper cervical dis- tween the target structure and the anterior border at the section was performed to reveal the carotid sheath anterior midpoint of the RCL in the craniocaudal plane (midway to the RCL. The posterior belly of the digastric muscle was between the origin and insertion of the muscle), directly reflected inferiorly, and the RCL was exposed. An infra adjacent to the IJV. The distance between the RCL and

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FIG. 4. A combined far-lateral transmastoid infralabyrinthine transcervical approach. Before (left) and after (right) detachment and reflection of the posterior belly of the digastric muscle and the RCL, and drilling of the jugular process. This combined approach provides exposure of the condylar fossa, jugular bulb within the mastoid, and IJV in the upper cervical region, with complete access to the jugular foramen from posterior, lateral, and anterolateral perspectives. The sigmoid sinus, jugular bulb, mastoid antrum, incus, fallopian canal, and lateral and posterior semicircular canals are skeletonized, and the presigmoid dura and endolymphatic sac are exposed.

CN VII was obtained by measuring the distance between tionships when approaching the craniocervical junction the anterosuperior corner of the RCL, at its insertion on from posterolaterally. The RCL originates along the su- the jugular process, and CN VII at its exit from the sty- perior and anterior portions of the C1TP and inserts on lomastoid foramen. The angles formed between the RCL the jugular process of the occipital bone. The RCL is one and CN IX, X, and XI within the jugular foramen, and of several suboccipital muscles that attach to the C1TP, between the RCL and the hypoglossal nerve within the including the superior oblique that inserts on the occipital hypoglossal canal, were measured in all specimens with bone below the superior nuchal line, the inferior oblique a digital protractor. that originates from the spinous process of C-2, and the splenius cervicis that originates from multiple thoracic Results spinous processes (Fig. 3A). The posterior belly of the digastric muscle inserts several millimeters anterior and In all 4 posterolateral approaches, the RCL was clearly lateral to the RCL, while the longissimus capitis—which exposed within the jugular foramen and high cervical re- travels superiorly from its origin in the cervical spine and gions and was found to maintain a constant relationship passes posteriorly behind the C1TP—inserts several mil- with the structures exiting the jugular foramen, the IJV limeters posterior and lateral to the RCL. The superior within the carotid sheath, and CN VII as it exits the stylomastoid foramen. oblique inserts along the inferior nuchal line, posterior to The RCL borders the extracranial neurovascular com- the insertion of the longissimus capitis, while the splenius partment of the upper retrostyloid parapharyngeal space capitis has a wide insertion laterally that covers the pos- traversed by the structures exiting the jugular foramen. terior belly of the digastric, RCL, longissimus capitis, and This extracranial compartment is a transitional space be- superior oblique muscles. tween the intracranial aspect of the jugular foramen and The RCL courses superiorly and the inferior oblique the cervical carotid sheath. For the purposes of this study, courses posteriorly from the C1TP, forming a right angle. we considered this compartment to be bounded by the oc- The superior oblique bisects this angle as it courses toward cipital condyle medially, the styloid process laterally, the its insertion site (Fig. 3A). The RCL, the superior oblique, RCL posteriorly, and the opening of the jugular foramen and a line connecting these 2 muscles along the occipital superiorly. The inferior boundary of this area is the point bone form what we term the condylar triangle (Fig. 3B). at which the lower CNs diverge and the IJV, ICA, and the In the 4 heads (8 sides) examined, the jugular process vagus nerve (CN X) converge within the carotid sheath. was an average of 17.3 mm (range 17–18 mm) superior to Within the jugular foramen and this extracranial neuro- the C1TP, and the styloid process was an average of 6.5 vascular compartment, the lower CNs travel several mil- mm (range 6–7 mm) anterior to the anterior aspect of the limeters outside the skull, in extremely close proximity, RCL’s insertion on the jugular process. before the ICA, IJV, and CN X meet and the glossopha- ryngeal (CN IX), accessory (CN XI), and hypoglossal (CN Vascular Relationships XII) nerves diverge in separate directions. The RCL maintains relatively constant relationships with several critical vascular structures, including the VA Musculoskeletal Relationships and the jugular venous system. The origin of the RCL The RCL has several notable musculoskeletal rela- overlays the C-1 foramen transversarium, where the ex-

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FIG. 5. Stepwise anatomical dissection of the jugular foramen, part I. A: An infralabyrinthine mastoidectomy with partial intracranial exposure of CN VII and the chorda tympani and skeletonization of the sigmoid sinus. The VA is visible as it turns posteriorly after exiting the C-1 transverse foramen before coursing medially to enter the dura. The IJV and ICA are within the carotid sheath, CN IX is anterolateral to the ICA, and CN XI and the IJV are directly anterior to the RCL. B: Removal of the mastoid tip and opening of the stylomastoid foramen improve exposure of CN VII. The jugular process is now visible superior to the RCL and anterolateral to the jugular tubercle. C: The IJV is retracted anteriorly to show CNs X and XII in the carotid sheath. D: The IJV and jugular bulb are removed, and CN VII is transposed to improve exposure of the jugular foramen. SCC = semicircular canal. traforaminal portion—between the C-1 foramen transver- Neural Relationships sarium and the dura—of the V3 segment of the VA courses The first structure located anteriorly to the RCL is CN 90° posteriorly (Figs. 5 and 6). Before entering the dura, XI, which lies between the medial aspect of the RCL and the extraforaminal portion of the V3 segment makes a the IJV, and is in some cases adherent to the carotid sheath. second 90° turn medially. The average distance from this CN X courses anterior to CN XI and directly medial to the medial turn to the posterior border of the RCL is 20.3 mm IJV. CN IX is anterior to CN X and is furthest from the (range 19–22 mm). RCL. CN XII travels obliquely, anteriorly, and inferiorly, The RCL lies directly posterior to the IJV, separated medial to CNs XI, X, and IX. only by the carotid sheath (Figs. 5A and B; 7). The anterior The anterior aspect of the insertion of the RCL on the portion of the RCL, as it inserts on the jugular process, jugular process is an average of 1.8 mm (range 1.5–2 mm) covers the posterior aspect of the opening of the jugular from CN VII as it exits from the stylomastoid foramen foramen. As the IJV turns posteriorly and ascends to form (Figs. 5B and 6). After exiting the stylomastoid foramen, the jugular bulb, it becomes superior to the RCL and the CN VII courses anteriorly toward the parotid gland, mov- jugular process (Fig. 5A). The ICA ascends anterior to the ing away from the RCL as it descends. RCL and anteromedial to the IJV to enter the carotid canal Intradurally, CN IX is the most superior of the lower and is an average of 6.2 mm (range 5.5–7 mm) anterior to CNs to enter the jugular foramen, and it travels anteriorly the top of the RCL. through the jugular foramen medial to the intrajugular

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FIG. 6. Stepwise anatomical dissection of the jugular foramen, part II. A: The occipital condyle is removed to expose the hypoglossal canal. CN XII is visible on both sides of the RCL. B: An occipital craniectomy is performed to expose the cerebellomedul- lary fissure. The CNs within the jugular foramen travel anteriorly and inferiorly forming a 120° angle with the RCL, until coursing anterior to the RCL, where they turn inferiorly to exit the jugular foramen and run parallel to the RCL. PICA = posterior inferior cerebellar artery. C: The intrajugular septum is drilled to expose the course of CN IX through the jugular foramen. D: CN XII is visible as it ascends through the hypoglossal canal at a 60° angle relative to the RCL and courses above the RCL before turning inferiorly. An instrument is passed through the distal aspect of the hypoglossal canal to show the peak of CN XII’s turn above the RCL as it enters the carotid sheath, medial to CNs X and XI.

septum. Of the CNs within the carotid sheath, CN IX is la, enters the hypoglossal canal, and courses anteriorly and the farthest from the RCL with an average distance of 9.2 superiorly, medial to the jugular process and RCL. CN XII mm (range 8.5–10 mm) from the top of the RCL. After then makes a sharp turn inferiorly, crossing the top of the crossing the plane of the RCL, CN IX courses inferiorly to RCL medially, to join the CNs of the jugular foramen as exit the jugular foramen medial to the styloid process and they enter the carotid sheath (Figs. 6C and 7). lateral to the ICA (Figs. 5D and 6). CNs X and XI originate as rootlets from the medulla, Condylar Triangle enter the jugular foramen together just inferior to CN IX, and travel anteriorly, lateral to the intrajugular septum, be- To facilitate identification of the occipital condyle, hy- fore turning inferiorly to wrap around the jugular process poglossal canal, and VA, we propose a novel triangle that and RCL (Figs. 6B and 7). At the superior aspect of the we term the condylar triangle—formed by the RCL an- RCL, the two nerves split, CN XI descends in close prox- teriorly, superior oblique posteriorly, and a line connect- imity to the RCL, just medial to the IJV, and CN X crosses ing these muscles along the occipital bone superiorly. This lateral to and then medial to the hypoglossal nerve, as it condylar triangle can be opened by detaching the superior descends into the neck. oblique to expose the posterior aspect of the occipital con- CN XII originates as rootlets from the anterior medul- dyle (Fig. 3C). The condylar triangle contains the anterior

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RCL, longissimus capitis, and other paraspinal muscles facilitate stabilization and lateral flexion of the head, during which there is compression of the structures exiting the jugular foramen. The RCL, longissimus capitis, and carotid sheath function as a protective barrier by encircling the IJV and the structures exiting the jugular foramen. This probable protective role of the RCL provides it with very constant neurovascular relationships that can be utilized by the surgeon. The first descriptions of the RCL as a surgical landmark for the jugular foramen and CN VII were performed by Katsuta et al. and Wen et al. in 1997 in their studies of the jugular foramen and far-lateral approach, respectively.8,14 Their findings were further elucidated by Rhoton in 2000 in his studies of the jugular foramen and far-lateral approach.12,13 While these authors briefly described the RCL in relation to the jugular process, jugular foramen, and CN VII, we present the first comprehensive cadaveric study of the RCL and its neural, vascular, and musculoskeletal relationships in order to demonstrate the utility of the RCL as an important landmark for avoiding neurovascular injury during approaches to the jugular foramen, and detail the surgical steps necessary to safely expose and detach the muscle. In addition, we propose the condylar triangle as a novel and useful landmark for identifying the occipital condyle, hypoglossal canal, and VA. FIG. 7. Illustration of the RCL and its anatomical relationships. Detailed The jugular foramen can be approached laterally depiction of the spatial relationships between the RCL, CN VII, and the through the mastoid and the upper neck, posteriorly lower CNs of the jugular foramen and hypoglossal canal with removal through the far-lateral approach, anterolaterally through of the IJV and occipital artery. CN VII is depicted at the stylomastoid the preauricular infratemporal approach, or anteriorly foramen several millimeters from the anterior border of the RCL at its through an endoscopic endonasal approach.5,9,10,13 When insertion on the jugular process. From posterior to anterior, CNs XI, approaching the jugular foramen anteriorly, the contents X, and IX can be seen descending, after exiting the jugular foramen, adjacent to the RCL. CN XII is observed as it exits the hypoglossal canal of the jugular foramen are encountered prior to the RCL; and descends medial to the other CNs with a more anterior trajectory. thus, the relevance of the RCL as a surgical landmark is Copyright Andy Rekito. Published with permission. limited to the posterolateral approaches, including the far- lateral and extended far-lateral, and the lateral approaches described herein, including the combined transmastoid third of the occipital condyle and provides a landmark for transcervical as well as the combined far-lateral transmas- the terminal segment of the hypoglossal canal. Additional- toid transcervical approaches (Fig. 8). ly, the condylar triangle contains the superior aspect of the In the conventional far-lateral approach for intracranial pathologies, the RCL can function as the anterior bound- genu of the V3 segment of the VA as it bends posteriorly toward the atlantooccipital membrane after exiting the C-1 ary of the approach, separating the far-lateral corridor foramen transversarium. from the contents of the jugular foramen (Figs. 3A and 8).2,6,7 For extended far-lateral approaches to the jugular foramen, the identification and reflection of the RCL, Discussion which overlays the structures exiting the jugular foramen, Tumors of the jugular foramen, including glomus tu- is the first step in safely exposing the jugular process, the mors, schwannomas, and meningiomas, are rare neuro- surrounding neurovascular structures, and the carotid surgical entities. The complex, dense, and deep nature of sheath.9,13 The RCL in this context is especially impor- this region complicates surgical access and necessitates tant in the presence of tumors that laterally displace the the use of precise surgical landmarks to avoid injury to closely spaced neurovascular structures exiting the jugu- critical neurovascular structures, including CNs VII and lar foramen. IX–XII, the ICA, IJV, and VA, especially in the presence When approaching primary lesions of the jugular fora- of anatomically distorting tumors.2,3 The RCL, due to its men laterally in the transmastoid infralabyrinthine trans- proximity to the jugular foramen and constant anatomical cervical approach, the RCL and the structures exiting the relationships, can function as a key surgical landmark for jugular foramen are encountered simultaneously (Fig. 4), early identification of and orientation around these critical diminishing the value of the RCL as a landmark for these structures. structures and the carotid sheath. However, the RCL re- The RCL and its relationship with the IJV was first de- mains a valuable and protective landmark for identifying scribed by Piffer et al. in 1980, who concluded that the the jugular process and the VA from lateral and anterolat- RCL is an important protective structure for the IJV.11 The eral trajectories.

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be split and reflected anteriorly and posteriorly. As the dissection proceeds anteriorly, the posterior belly of the digastric muscle can be identified in the digastric groove and separated from the sternocleidomastoid and splenius capitis muscles. The superior oblique muscle can be identified and reflected anteriorly and inferiorly to expand the condylar triangle and expose the posterior aspect of the occipital condyle. Conclusions The RCL is an important surgical landmark that allows for early identification of the critical neurovascular structures when performing posterior and/or lateral approaches to the jugular foramen, especially in the presence of anatomically displacing tumors. The condylar triangle is a novel and useful landmark for identifying the terminal segment of the hypoglossal canal as well as the superior aspect of the VA at its exit from the C-1 foramen transversarium.

References 1. Alvernia JE, Fraser K, Lanzino G: The occipital artery: a mi- croanatomical study. Neurosurgery 58 (1 Suppl):ONS114– FIG. 8. The RCL in different surgical trajectories. Depiction of the RCL in ONS122, 2006 relation to the far-lateral and extended far-lateral (left arrow), transmas- 2. Anichini G, Evins AI, Boeris D, Stieg PE, Bernardo A: toid (upper arrow), and transcervical (right arrow) surgical trajectories. Three-dimensional endoscope-assisted surgical approach to Copyright Andy Rekito. Published with permission. the foramen magnum and craniovertebral junction: minimiz- ing bone resection with the aid of the endoscope. World Neurosurg 82:e797–e805, 2014 The condylar triangle—which we define as being 3. Bernardo A, Evins AI, Visca A, Stieg PE: The intracranial formed by the RCL anteriorly, the superior oblique pos- facial nerve as seen through different surgical windows: an teriorly, and the occipital bone superiorly—contains the extensive anatomosurgical study. Neurosurgery 72 (2 Suppl anterior third of the occipital condyle and provides a novel Operative):ons194–ons207, 2013 and useful landmark for identifying the superior aspect of 4. Berra L, Regaert B, Cohen J, Tebo C, Stieg PE, Bernardo A: the genu of the V3 segment of the VA as it bends poste- A combined far lateral, sublabyrinthine, transpetrosal, trans- riorly toward the atlantooccipital membrane after exiting cervical approach to the jugular foramen, anterior brainstem, the C-1 foramen transversarium as well as the terminal and clivus. Skull Base 21:A102, 2011 segment of the hypoglossal canal (Fig. 3B and C). 5. Dallan I, Bignami M, Battaglia P, Castelnuovo P, Tschab- itscher M: Fully endoscopic transnasal approach to the In conventional far-lateral approaches, where dissec- jugular foramen: anatomic study and clinical considerations. tion of the C1TP is often limited, the RCL is not typi- Neurosurgery 67 (3 Suppl Operative):ons1–ons8, 2010 cally exposed. Even in extended far-lateral transcondylar 6. Fukuda H, Evins AI, Burrell JC, Stieg PE, Bernardo A: A approaches, such as the extreme lateral, the RCL is often safe and effective technique for harvesting the occipital removed from the jugular process without prior identifi- artery for posterior fossa bypass surgery: a cadaveric study. cation. When approaching primary lesions of the jugular World Neurosurg 82:e459–e465, 2014 foramen via the extended far-lateral corridor, wherein 7. Fukuda H, Evins AI, Iwasaki K, Hattori I, Murao K, Ku- identification of the RCL can be clinically helpful, the skin rosaki Y, et al: The role of alternative anastomosis sites in incision must provide exposure of the mastoid tip, C1TP, occipital artery-posterior inferior cerebellar artery bypass in the absence of the caudal loop using the far-lateral approach. and more posterior exposure of the condylar fossa. Ad- J Neurosurg [epub ahead of print April 1, 2016. DOI: ditionally, if high cervical exposure is required, the inci- 10.3171/2015.11.JNS151385] sion must extend into the neck to the anterior border of 8. Katsuta T, Rhoton AL Jr, Matsushima T: The jugular fora- the sternocleidomastoid muscle. While the suboccipital men: microsurgical anatomy and operative approaches. Neu- muscles are typically elevated en bloc to reduce bleeding rosurgery 41:149–202, 1997 and maintain a solid muscle mass for wound closure that 9. Komune N, Matsushima K, Matsushima T, Komune S, helps prevent CSF leakage, the posterior belly of the digas- Rhoton AL: Surgical approaches to jugular foramen schwan- tric muscle and the suboccipital triangle must be dissected nomas: an anatomic study. Head Neck 38 (Suppl 1):E1041– separately in order to safely expose the RCL. E1053, 2016 10. Lee DLY, McCoul ED, Anand VK, Schwartz TH: Endo- To accomplish this, the superficial and middle mus- scopic endonasal access to the jugular foramen: defining the cle layers should be detached and reflected from medial surgical approach. J Neurol Surg B Skull Base 73:342–351, to lateral using subperiosteal dissection. When using a 2012 hockey-stick incision, the muscles can be reflected infe- 11. Piffer CR, Soares JC, Garcia PJ: [Relations of the rectus riorly; when using a C-shaped or liner incision, they can capitis lateralis muscle with the first portion of the internal

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jugular vein (author’s transl).] Anat Anz 149:333–336, 1981 Acquisition of data: Cohen, Evins, Lapadula, Arko. Analysis (Fr) and interpretation of data: Bernardo, Cohen, Evins, Lapadula, 12. Rhoton AL Jr: The far-lateral approach and its transcondylar, Arko. Drafting the article: Cohen, Evins. Critically revising the supracondylar, and paracondylar extensions. Neurosurgery article: Bernardo, Cohen, Evins. Reviewed submitted version 47 (3 Suppl):S195–S209, 2000 of manuscript: all authors. Approved the final version of the 13. Rhoton AL Jr: Jugular foramen. Neurosurgery 47 (3 manuscript on behalf of all authors: Bernardo. Administrative/ Suppl):S267–S285, 2000 technical/material support: Evins. Study supervision: Bernardo, 14. Wen HT, Rhoton AL Jr, Katsuta T, de Oliveira E: Microsur- Evins, Stieg. gical anatomy of the transcondylar, supracondylar, and paracondylar extensions of the far-lateral approach. J Neurosurg Supplemental Information 87: 555–585, 1997 Previous Presentations Portions of this work were presented at the proceedings of the Disclosures 27th Annual Meeting of the North American Skull Base Society The authors report no conflict of interest concerning the materi- in Scottsdale, Arizona, February 12–14, 2016. als or methods used in this study or the findings specified in this paper. Correspondence Antonio Bernardo, Weill Cornell Medical College, 525 East Author Contributions 68th St., Box 99, New York, NY 10065. email: anb2029@med. Conception and design: Bernardo, Cohen, Evins, Lapadula, Arko. cornell.edu.

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