Download Rectus Capitis Lateralis

Rectus Capitis Lateralis: An Important Landmark for
Posterolateral Approaches to the Jugular Foramen
Michael A. Cohen MD1,2, Brandon T. Pagan MD3, Alexander I. Evins PhD1,
Gennaro Lapadula MD4, Philip E. Stieg, MD1, Antonio Bernardo, MD1
1Microneurosurgery
Skull Base and Surgical Innovations Laboratory, Department of Neurological Surgery, Weill Cornell Medical College
2Department of Neurological Surgery, Rutgers New Jersey Medical School
3University of Puerto Rico Medical School
4Departement of Neurology and Psychiatry, Neurosurgery, “Sapienza” University of Rome, Rome, Italy
A
INTRODUCTION
B
The jugular foramen can be approached from
posteriorly during a far lateral approach, from
laterally during a trans-mastoid approach. The
intricacy of surgical anatomy of the upper
cervical region and jugular foramen requires the
identification of anatomical landmarks to help in
protecting
the
neurovascular
structures.
C
The rectus capitis lateralis (RCL) muscle is a
small deep muscle, located superolateral to the
Figure 1. (A) The RCL is located just anterior to the superior oblique,
suboccipital triangle, that connects the
originates from the C1 transverse process and inserts on the jugular process,
transverse process of C1 (C1TP) with the jugular medial to the mastoid tip. A triangle (yellow) is formed by the RCL, superior
process of the occipital bone. The RCL is an oblique, and a line connecting these two muscles along the skull (red dotted
line). The OA generally travels along this line in its intramuscular segment.
excellent landmark aiding in localization of the (B) The OA passes between the posterior belly of the digastric muscle and
the RCL and forms the roof of the condylar triangle.
IJV within the carotid sheath, the contents of the
jugular foramen as they exit the skull, and facial
E
nerve as it exits the stylomastoid foramen.
METHODS
A horseshoe shaped incision was made and
the muscles of the suboccipital triangle were
dissected on 3 preserved cadaveric specimens
injected with colored latex into the arterial and
venous systems. The incision was extended into
the neck and a high cervical dissection of the
facial nerve and contents of the carotid sheath
was performed. The RCL was exposed anterior
to the posterior belly of the digastric muscle. A
mastoidectomy is performed, skeletonizing the
sigmoid sinus, jugular bulb, and facial nerve
within the fallopian canal. The mastoid tip is
removed, exposing the jugular process and RCL.
The jugular bulb is removed, exposing cranial
nerves IX, X, and XI, which are dissected and
exposed within the jugular foramen. The
hypoglossal canal is exposed within the occipital
condyle.
RESULTS
Musculoskeletal Relationships
The RCL courses superiorly and the inferior
oblique courses posteriorly from the C1TP,
forming a right angle. The superior oblique
bisects this angle as it courses toward its
insertion site (Figure 1A). A second triangle is
formed by the RCL, the superior oblique, and a
line connecting these two muscles along the
occipital bone (Figure 1B). The occipital artery
coursed along this line connecting the RCL and
superior oblique in all specimens studied. The
RCL originates along the superior and anterior
portions of the C1TP and inserts on the jugular
process of the occipital bone (Figure 2). The
jugular process is an average of 17.3 mm (range
17 – 18 mm) superior from the C1TP. The styloid
process lies 6.5 mm (range 6 – 7 mm) anterior to
the anterior aspect of the RCL insertion site on
the jugular process. The jugular process forms
the floor of the jugular bulb and the posterior
aspect of the jugular foramen meatus.
A
G
B
D
F
H
Figure 2. The RCL originates on the C1TP and inserts on the jugular
process (shaded in pink). The RCL separates the far lateral approach
(purple) and the transcondylar variant (green) from the jugular foramen
(dark blue), anteriorly.
Vascular Relationships
The RCL lies directly posterior to the IJV,
separated only by the carotid sheath (Figure 3).
The IJV turns posteriorly as it ascends to form the
jugular bulb, superior to the RCL and jugular
process. Both the anterior and superior surfaces
of the RCL are surrounded by the jugular venous
system. The RCL origin covers the C1 transverse
foramen, where the vertebral artery (VA) makes
its posterior turn (Figure 3). The average distance
from the medial turn of VA, just before piercing
the dura, to the posterior border of the RCL is
20.3 mm (range 19 – 22 mm). The ICA ascends
anteromedial to the RCL and IJV to enter the
carotid canal. The ICA is an average of 6.2 mm
(range 5.5 – 7 mm) anterior to the top of the RCL.
Neural Relationships
The anterior aspect of the RCL insertion on the
jugular process is an average of 1.8 mm (range
1.5 – 2 mm) from the facial nerve as it exits the
stylomastoid foramen (Figure 3A and 3B). The
glossopharyngeal nerve travels anteriorly in
isolation through the jugular foramen medial to
the intrajugular septum. After crossing the plane
of the RCL, it turns inferiorly to exit the jugular
foramen medial to the styloid process and lateral
to the ICA (Figure 3D). The glossopharyngeal
nerve is the furthest of the cranial nerves within
the carotid sheath from the RCL, with an average
distance of 9.2 mm (range 8.5 – 10 mm) at the
top of the RCL. The vagus and accessory nerves
enter the jugular foramen together, several
millimeters inferior to the glossopharyngeal nerve.
They wrap around the jugular process and RCL
(Figure 3F), where the two nerves split. The
accessory nerve descends in close proximity the
RCL, just medial to the IJV, whereas the vagus
nerve crosses first lateral to and then medial to
the hypoglossal nerve, as it descends into the
neck. The hypoglossal nerve enters a bony canal
through the occipital condyle, coursing anteriorly
and superiorly, posteromedial to the RCL, and
joins the cranial nerves of the jugular foramen as
they enter the carotid sheath together (Figure
3G).
Figure 3. (A) Occipital bone and condyle, jugular process, C1 posterior arch and
transverse process (C1TP), and VA are exposed. The RCL originates from the
C1TP and inserts on the jugular process. A sub-labyrinthine mastoidectomy is
performed with exposure of the mastoid segment of the facial nerve and the
sigmoid sinus. High cervical dissection is performed, isolating the IJV and ICA
within the carotid sheath. The extracranial facial, glossopharyngeal, and
accessory nerves are identified. (B) The mastoid tip is removed and the
stylomastoid foramen opened to show the facial nerve and the jugular process.
(C) The IJV is retracted anteriorly to show the vagus, accessory, and
hypoglossal nerves in the carotid sheath. (D) The IJV and jugular bulb are
removed and the facial nerve is transposed to improve exposure of the jugular
foramen. (E) Occipital condylectomy is performed to expose the hypoglossal
canal. The hypoglossal nerve is seen on both sides of the RCL. (F) All cranial
nerves within the jugular foramen travel anteriorly and inferiorly through the
jugular foramen, forming a 120-degree angle with the RCL. After passing
anterior to the RCL, the nerves turn inferiorly to exit the jugular foramen parallel
to the RCL. (G) The hypoglossal nerve ascends through the hypoglossal canal
at a sharp 60-degree angle, relative to the RCL, climbing above the RCL and
making a sharp turn inferiorly after entering the carotid sheath. A wire is passed
through the distal aspect of the hypoglossal canal to show the peak of the turn
that the hypoglossal nerve makes above the RCL to enter to the carotid sheath,
medial to the vagus and accessory nerves. (H) The intrajugular septum has
been drilled to expose the course of the glossopharyngeal nerve through the
jugular foramen.
CONCLUSION
The RCL muscle is an important anatomic
landmark, separating the far lateral approach from
the jugular foramen and facial nerve. A thorough
understanding of the microsurgical anatomy of the
RCL and its musculoskeletal, vascular, and neural
relationships is necessary to safely perform
combined approaches to the foramen magnum and
jugular foramen.
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