Retromastoid-transmuscular identification and harvest of the occipital artery during retrosigmoid craniotomy

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OBJECTIVE

Harvesting the occipital artery (OA) is challenging. The subcutaneous OA is usually found near the superior nuchal line and followed proximally, requiring a large incision and risking damage to the superficially located OA. The authors assessed the anatomical feasibility and safety of exposing the OA through a retromastoid-transmuscular approach.

METHODS

Using 10 cadaveric heads, 20 OAs were harvested though a 5-cm retroauricular incision placed 5 cm posterior to the external auditory meatus. The underlying muscle layers were sequentially cut and recorded before exposing the OA. Changes in the orientation of muscle fibers were used as a roadmap to expose the OA without damaging it.

RESULTS

The suboccipital segment of the OA was exposed without damage after incising two consecutive layers of muscles and their investing fasciae. These muscles displayed different fiber directions: the superficially located sternocleidomastoid muscle with vertically oriented fibers, and the underlying splenius capitis with anteroposteriorly (and mediolaterally) oriented fibers. The OA could be harvested along the entire length of the skin incision in all specimens. If needed, the incision can be extended proximally and/or distally to follow the OA and harvest greater lengths.

CONCLUSIONS

This transmuscular technique for identification of the OA is a reliable method and may facilitate exposure and protection of the OA during a retrosigmoid approach. This technique may obviate the need for larger incisions when planning a bypass to nearby arteries in the posterior circulation via a retrosigmoid craniotomy. Additionally, the small skin incision can be enlarged when a different craniotomy and/or bypass is planned or when a greater length of the OA is needed to be harvested.

ABBREVIATIONS EAM = external auditory meatus; LC = longissimus capitis; MEF = mastoid emissary foramen; OA = occipital artery; OG = occipital groove; SCM = sternocleidomastoid; SpC = splenius capitis.

Article Information

Correspondence Mark C. Preul: Barrow Neurological Institute, St. Joseph’s Hospital, Phoenix, AZ. neuropub@barrowneuro.org.

INCLUDE WHEN CITING Published online July 12, 2019; DOI: 10.3171/2019.4.JNS19323.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Overview of the main segments of the OA from a posterior perspective in a cadaveric specimen. 1 = the digastric segment that originates from the external carotid artery and runs medial to the posterior belly of digastric muscle and ends as the OA exits the OG (only the distal portion of this segment is shown). 2 = the suboccipital segment that extends from the OG to the region near the superior nuchal line and just before the OA pierces the muscular tendons attached to the superior nuchal line to become subcutaneous. 3 = the subgaleal segment. PBD = posterior belly of digastric muscle; RCPmin = rectus capitis posterior minor muscle; SO = superior oblique muscle; VA = vertebral artery. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

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    Stepwise depiction of the retromastoid-transmuscular technique for exposing the left OA. The compass in panel A applies to all panels. A: A curvilinear incision is placed about 5 cm behind the EAM. B: Dissecting the subcutaneous tissue exposes the vertically oriented fibers of the SCM muscle (double arrow lines). C: Dissection of SCM muscle fibers exposes the deep SCM fascia. D: Opening the deep SCM fascia exposes the anteroposteriorly oriented fibers of SpC muscle (double arrow curved lines). E: Dissection through the SpC fibers may expose a fascial layer inside the SpC muscle (intrasplenial fascia). F: Opening the intrasplenial fascia exposes the deep belly of SpC muscle with fibers running in the same direction as the superficial SpC belly (double arrow curved lines). G: Incising the deep SpC fibers exposes the deep fascia of the SpC muscle. Note the LC muscle at the inferior aspect of the cut SpC fibers with fiber orientation similar to that of SpC muscle (double arrow line). H: Opening the deep SpC fascia exposes the suboccipital OA segment. Deep to the OA, the vertically oriented fibers of posterior belly of digastric muscle (lateral) and superior oblique muscle (medial) are seen (double arrow curved lines). Ant. = anterior; Inf. = inferior; PBD = posterior belly of digastric muscle; SO = superior oblique muscle. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

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    Stepwise dissection of a cadaveric specimen showing the anatomical basis of the retromastoid-transmuscular approach on the left side. The compass in panel A applies to all panels. A: The SCM and trapezius compose the first layer of the craniovertebral junction muscles. Note the vertical orientation of the SCM fibers. The (distal) subgaleal segment of the OA is visible after it pierces the tendons of muscles inserted onto the superior nuchal line. B: The SCM and trapezius muscles are reflected and the oblique fibers of the SpC muscle running from the posterior to anterior are exposed. C: Detachment of the SpC muscle exposes the underlying suboccipital segment of the OA at the level of the mastoid process as well as the LC and semispinalis capitis muscles. The relationship between the OA and the LC muscle can be variable. It can run under, over, or through the LC muscle. However, the OA always runs under the SpC muscle. The transmuscular technique exposes the suboccipital OA superior to the longissimus capitis muscle (marked by the dashed lines in C and D). D: Reflecting the longissimus capitis and semispinalis capitis muscles reveals the relationship between the OA and the deep muscles of the craniovertebral junction. Note the OA emerging between the superior oblique and posterior belly of digastric muscle. Also note the proximity of the OA with MEF. br. = branch; GON = greater occipital nerve; IJV = internal jugular vein; IO = inferior oblique; Lat. = lateral; LON = lesser occipital nerve; PBD = posterior belly of digastric muscle; RCPmaj = rectus capitis posterior major; RCPmin = rectus capitis posterior minor; SO = superior oblique muscle; Sup. = superior. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

  • View in gallery

    Intraoperative exposure of the OA using the retromastoid-transmuscular technique. The patient is placed in the lateral decubitus position. A: A left-sided retromastoid C-shaped incision is made. B: The skin is reflected to reveal the underlying SCM muscle with its investing fascia. Arrows show the vertical trajectory of the SCM muscle fibers. C: Following incision of the SCM muscle, the underlying SpC muscle (with fibers running from posterior/medial to anterior/lateral, shown with two small double arrow lines) is exposed and incised. D: Under the deep fascia of the SpC muscle, the OA and its deep descending branch (shown with dashed arrows) are exposed and isolated. Ant. = anterior; Inf. = inferior. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

  • View in gallery

    Bone anatomy of the mastoid process and suboccipital regions from different perspectives and the relationship between bony landmarks and the course of the suboccipital OA (red arrow). The exposed OA segment is shown with dashed lines. The delimited areas and numbers represent the insertion of craniovertebral junction muscles. A: The posterior-lateral view of the left mastoid-suboccipital region. After emergence from the OG, which lies lateral to the inferior nuchal line, the suboccipital OA runs close to the occipitomastoid suture and MEF. This is the segment of the OA that is exposed with a retromastoid-transmuscular approach. Note that the exposed segment of the OA is at the level of the mastoid process. B: The posterior-inferior view. Note how the OA lies underneath the SpC muscle (#2). The transmuscular technique exposes the OA just superior to the LC muscle (#3). C: The lateral-inferior view. Deep to the exposed OA, the superior oblique muscle (#5) is found medially, and the digastric muscle (#4) can be found laterally. Note the exposed segment of the OA through the retromastoid-transmuscular approach is almost at the level of EAM. 1 = SCM muscle; 2 = SpC muscle; 3 = LC muscle; 4 = digastric muscle; 5 = superior oblique; 6 = rectus capitis posterior major; 7 = rectus capitis posterior minor. DG = digastric groove; EOP = external occipital protuberance; INL = inferior nuchal line; MEF = mastoid emissary foramen; OG = occipital groove; OMS = occipitomastoid suture; SNL = superior nuchal line. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

  • View in gallery

    Cadaveric dissections showing the nearby venous channels, as well as the descending muscle and transmastoid branches of the OA (compass applies to both panels). A: The retromastoid-transmuscular technique exposes the OA superior to the level of the LC muscle. This segment of the OA is in close proximity to venous channels (colored in blue) connected with the nearby MEF. Also, note the descending muscular branch of the OA originating at this level. B: The left OA is shown emerging between the posterior belly of digastric and superior oblique muscles. Note the descending muscular and transmastoid branches. br. = branch; Lat. = lateral; PBD = posterior belly of digastric muscle; SO = superior oblique muscle; Sup. = superior. Copyright Barrow Neurological Institute. Published with permission. Figure is available in color online only.

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