Abstract

BackgroundC2 nerve root schwannomas are rare and may be hourglass or dumbbell-shaped at the craniocervical junction. We describe the clinical/radiological features and treatment outcomes of patients with dumbbell C2 schwannomas operated through a far lateral approach and the technical details of this approach.

MethodsBetween 2019 and 2024, seven consecutive patients underwent surgery for dumbbell C2 schwannomas at the Hospital de Especialidades del Centro Médico Nacional Siglo XXI in Mexico City, Mexico. Data regarding clinical presentation, tumor location, and surgical results were investigated retrospectively in institutional databases.

ResultsThere were 5 males (71.4%) and 2 females (28.5%); the mean age was 50.4 years (range 36–75). The average duration of symptoms before surgery was 16.7 months (range 8–35). Motor deficit (85.7%) and headache (57.1%) were the most frequent symptoms. In all cases, gross total resection (GTR) was successfully achieved. There were no post-surgical complications reported. The mean follow-up time was 21.4 months (range 1–54). Six patients (85.7%) referred completely recovered from their symptoms.

ConclusionDumbbell C2 schwannomas pose a surgical challenge due to the adjacent anatomical structures involved. The far lateral approach enables GTR of these tumors with minimal neurovascular manipulation and excellent functional outcomes.

Keywords: C2 schwannoma, Dumbbell tumor, Far lateral, Spinal schwannoma

INTRODUCTION

Schwannomas represent the second most prevalent tumor among spinal canal neoplasms.[ 28 ] The incidence of spinal schwannomas (SS) is estimated to be between 0.3 and 0.4 cases/100,000 individuals annually.[ 23 , 25 ] SS are grade World Health Organization 1 tumors that develop from the innermost layer of the nerve sheath and account for 80% of all tumors in this location.[ 25 ] They are generally intradural extramedullary tumors, but they can also grow extradural (10%) or in a combined intra-extradural manner (10–15%), taking on an hourglass or dumbbell shape. Rarely intramedullary schwannomas have been identified and reported.[ 3 , 26 ] The incidence age is typically between 65 and 75 years, and there are no identified risk factors for sporadic cases of SS.[ 3 , 28 ]

SS can manifest at any level of the spinal column, with the cervical region being the most frequently affected, followed by the lumbar region.[ 1 ] Schwannomas of the first two cervical nerve roots are rare and account for 5.3% of all SS.[ 6 , 9 ] Surgery is the mainstay of treatment and is indicated for patients with progressive neurological symptoms. C2 schwannomas are distinctive due to the complex anatomical relationships at the craniovertebral junction (CVJ). In addition, they are often large and dumbbell-shaped, which poses technical challenges for surgical management. Different surgical approaches can be used; however, achieving gross total resection (GTR) in tumors with these features may have a lower success rate.[ 11 , 21 , 29 ] The far lateral approach provides advantages for managing these tumors, minimizing retraction, and improving the visibility of the surgical field.[ 14 , 29 ] We present a consecutive series of seven patients with dumbbell C2 schwannomas resected through a far lateral approach to achieving GTR.

MATERIALS AND METHODS

Study design

This study was observational, descriptive, and retrospective. The Local Health Research Committee at our hospital approved it (F-2024-3601-258).

Study population

Between 2019 and 2024, seven consecutive patients underwent surgery for dumbbell C2 schwannomas at the Hospital de Especialidades del Centro Médico Nacional Siglo XXI in Mexico City, Mexico. The clinical, radiological, and surgical profiles were retrospectively analyzed from institutional databases. All patients underwent a preoperative magnetic resonance imaging (MRI) scan to evaluate the extent and configuration of the tumor and a computed tomography (CT) scan to assess the degree of bone involvement in the atlantoaxial joint and to determine the stability of the CVJ to evaluate the need for fixation. In addition, preoperative CT angiography or MRI angiography was conducted to evaluate the course of the vertebral artery (VA). An immediate, simple CT scan was performed on all patients during their immediate post-surgical follow-up. Tumors were classified according to the Eden classification: type I, intradural and extradural; type II, intradural, extradural, and paravertebral; type III, extradural and paravertebral; and type IV, foraminal, and paravertebral.[ 8 ] Tumor localization within the spinal canal was categorized as anterior, anterolateral, posterolateral, and posterior types. An MRI of the CVJ was performed 2 months postoperatively to assess the extent of tumor removal. Preoperative and postoperative clinical symptoms were evaluated using the modified Japanese Orthopedic Association (mJOA) score for evaluating cervical myelopathy.[ 27 ]

Surgical procedure

The patient was positioned in the park bench position and the head was fixed in a Mayfield three-pin head holder. The head was flexed so that only two to three fingers could fit between the patient’s chin and sternum, then rotated ipsilaterally toward the tumor (5–10°) and finally tilted slightly (20–30°) toward the contralateral shoulder. The upper arm was pulled away from the field using adhesive tape. The contralateral arm was secured between the head holder and the end of the operating table, always protecting the axilla with cotton or a foam roll to prevent brachial plexus injury. In this position, the mastoid was the highest point of the field [ Figure 1a ].

Figure 1:

(a) Park bench position for a right far lateral approach. (b) The incision involves the mastoid tip, superior nuchal line, and midline from inion to C4. (c) Image showing mobilization of the nuchal muscles in a single block by subperiosteal dissection. (d) Surgical view showing occipital craniotomy (white arrow), C1 hemilaminectomy, and extradural component of the tumor (white asterisk).

A classic reverse hockey stick incision was made. This incision begins at the mastoid tip, ascends to the superior nuchal line, curves medially to reach the inion, and then proceeds downward to C4 [ Figure 1b ]. We initiated the incision from the inion to the mastoid tip, following the superior occipital line, then continued with the midline portion along the ligamentum nuchae, from inion to the spinous process of C4, deepening the dissection until we identified the spinous process of C2, followed by the posterior tubercle of C1, and finally the atlanto-occipital membrane. The nuchal muscles were reflected (from upward to downward) in a single block in a subperiosteal plane until reaching the inferior occipital line. The soft tissue below the inferior occipital line, the C1 arch, and the upper edge of the C2 lamina was dissected subperiosteally from medial to lateral, starting from the midline and followed C1’s lower border, ensuring to avoid any venous bleeding caused by the rupture of the vertebral plexus or a vascular injury from the sulcus arteriosus found on the superior side. Subsequently, the tissue between the foramen magnum (FM) and the C1 vertebral space was meticulously dissected in a medial-to-lateral direction. Evidence of bleeding from the surrounding venous plexus suggests proximity to the VA [ Figure 1c ]. On locating the VA at the level of its groove, a hemilaminectomy was performed, slightly overlapping it toward the contralateral side. When deemed necessary, an ipsilateral C2 hemi-semi-laminectomy was also implemented. Following this, the endosteal dura mater layer was carefully separated from the bone at the level of the FM. A craniectomy measuring three by three centimeters was then performed, encroaching on the midline only at its lower edge at the level of the FM. It was determined that drilling of the occipital condyle was not required [ Figure 1d ].

The dura was opened with a laterally based curvilinear incision that passes medially to the entry point of the V3 segment of the VA. Usually, it is unnecessary to mobilize the VA because schwannomas rarely encase it. The dura flap was referred to with several sutures, which are important for enhancing exposure. When the tumor was larger in the intradural space, the intradural component was debulked internally, and its capsule was dissected away from the neurovascular structures, after which the extradural tumor was resected through its capsule. When the extradural component was larger, the tumor was debulked, and the extradural tumor was resected first; once this was completed, the dura was opened, as previously mentioned, to remove the intradural component [ Figure 2 ] finally. After ensuring hemostasis, a watertight dural closure was performed. Finally, the myocutaneous flap was tightly closed.

Figure 2:

Intraoperative images of a microsurgical resection of an Eden type II schwannoma through a right far lateral approach. (a and b) The tumor had a significant extradural component (black asterisk) that was first removed, followed by a lateral curvilinear dural opening for intradural resection. (c) The tumor compressed the anterior spinal cord (black asterisk) and contacted the V4 segment (black arrow). (d) Manipulation of the intradural component (black arrow) is feasible with minimal neurovascular retraction.

RESULTS

Demographic and clinical features

A total of seven patients with schwannomas arising from C2 nerve roots were included in the study [ Table 1 ]. Among them were 5 males (71.4%) and 2 females (28.5%); the mean age was 50.4 years (range 36–75). The average duration of symptoms before surgery was 16.7 months (range 8–35). Patients presented with various symptoms. The most common symptom was a motor deficit, which ranged from weakness to hemiplegia, observed in up to 85.7% of cases. Many patients reported headaches (57.1%) and other sensitivity deficits, including paresthesia or dysesthesia (71.4%). Occipital or neck numbness was reported in 42.8%. Only one patient presented with urinary sphincter disturbance (14.2%). In the clinical history, there is only one patient diagnosed with neurofibromatosis type 2 (NF2) who has a history of prior convexity meningioma excision surgery.

Table 1:

Summary of clinical and radiological characteristics of the study population.

Radiological findings

In preoperative MRI, all lesions were dumbbell-shaped. Based on the Eden scale, one tumor was classified as type I, four were type II, and two were type III [ Figure 3 ]. Regarding intraspinal location, posterolateral (57.1%) and anterolateral (42.8%) presentations were observed. The VA compression was observed in 42.8% of cases.

Figure 3:

Preoperative and postoperative images of three cases according to the Eden scale. Eden type I case: (a and b) sagittal and axial T1W gadolinium (Gd-T1W) magnetic resonance images (MRI) showing a large anterolateral and intradural tumor causing significant spinal cord compression (white arrowheads). (c and d) Axial and sagittal T2W images showing gross total resection and myelopathic spinal cord changes (white arrow). Eden type II case: (e and f) coronal and axial Gd-T1W images showing a tumor involving the intra- and extradural space with extension to the contralateral vertebral artery (white arrowheads) and severe compression (red arrowheads). (g and h) Axial and coronal Gd-T1W images showing gross total resection (GTR) and spinal cord space recovery. Eden type III case: (i and j) coronal section showing an enhancing lesion in the extradural space with transforaminal extension shown on the axial T2W section. (k and l) Postoperative MRI sequences showing GTR.

Postoperative clinical outcomes

A far lateral approach was used in all patients. C2 hemi-semi laminectomy was performed in only two cases [ Table 2 ]. GTR resection was achieved and confirmed through postoperative MRI in each case [ Figure 3 ]. Our series showed no intraoperative or postoperative complications. The mean follow-up duration was 21.4 months (range 1–54). In 85.7% of cases, patients reported an overall improvement in their symptoms. The mean mJOA score improved from 10.7 (range 3–15) preoperatively to 17 (range 13–18) postoperatively [ Table 2 ].

Table 2:

Summary of surgical techniques, clinical outcome, and follow-up data.

DISCUSSION

Schwannomas represent one-third of the primary spinal tumors and can occur at any level along the longitudinal axis.[ 9 , 23 - 25 ] SS are typically benign, solitary, well-circumscribed, and encapsulated intradural extramedullary lesions.[ 19 ] Sporadic schwannomas tend to be solitary neoplasms, whereas, in patients with NF2, multiple schwannomas can appear. Patients with NF2 are associated with schwannomas up to 56%.[ 3 , 28 ] SSs arising from the first two cervical nerve roots are infrequent and represent 18% of cervical SS.[ 5 , 9 ] In this series, only one patient had a history of NF2.

Patients with C2 schwannomas initially experience local symptoms such as neck pain or numbness in the suboccipital region.[ 10 , 29 ] In 82% of cases, patients have some degree of myelopathy manifested as motor or sensitive deficits. Other symptoms, such as sphincter disturbance, may appear in 28% of cases.[ 10 , 18 , 29 ] In our series, 85.7% presented some type of motor symptom, from motor weakness to hemiplegia. Only one patient had urinary sphincter disturbance, which correlates with severe myelopathy and the time of evolution before surgery.

On MRI, the tumors are typically predominantly isointense on T1-weighted images, hyperintense on T2-weighted images, and exhibit a homogeneous appearance after gadolinium administration.[ 10 , 18 ] Other radiological findings, such as the relationship of the tumor with VA or bony changes, can be shown using angio-CT or angio-MRI.[ 29 ] In this series, 57.1% of the tumors were classified as Eden II type, with a predominance of posterolateral intraspinal locations. The VA was involved in 42.8% of our cases, where it was found to be compressed by the tumor.

C1–C2 schwannomas are particularly interesting due to their location at the CVJ. The CVJ is a region of complex anatomy that includes the occipital bone and condyles, the atlas, and the axis, along with the lower cranial nerves (CN), C1–C2 nerves, and posterior vertebral circulation. These structures should be taken into account for operative planning concerning schwannomas at the CVJ.[ 17 , 20 , 29 ] Furthermore, schwannomas in this area are more likely to be large or dumbbell-shaped compared to those at other spinal levels. Dumbbell features are present in 45–70.6% of C1–C2 schwannoma cases.[ 6 , 9 , 29 ] More complex procedures may be necessary than a standard posterior approach for dumbbell tumors.[ 15 ] Dumbbell C2 schwannomas are closely associated with important neurovascular structures. They extend along the course of the C2 nerve and can displace, compress, or erode adjacent structures. Typically, they originate from the dorsal root and may compress various CNs. CN XI is located ventrally and medially, CN IX and X are positioned superiorly, while CN XII is situated anteriorly and superiorly. The fourth segment of the VA may be compressed anteriorly and superiorly, and the upper spinal cord can be displaced medially.[ 5 , 32 ]

Management strategies and outcomes

The standard treatment for SS is GTR, with surgical routes varying based on the tumor’s location and origin in the spine.[ 15 ] Multiple surgical approaches have been described to enhance safe tumor dissection, precise exposure, and control over critical neurovascular structures, achieving GTR rates between 84.3% and 93.3%.[ 1 , 4 , 12 ] For small cervical schwannomas confined to the intradural space and not extending laterally, a posterior midline approach with partial or total laminectomy is preferred.[ 19 ] Minimally invasive techniques such as hemilaminectomy, hemi-semi-laminectomy, and interlaminar approaches through the posterior route have been outlined, each with its advantages and disadvantages; these may be considered for specific cases, such as small tumors without neurovascular involvement.[ 7 , 10 , 30 , 33 , 34 ]

While the posterior approach is straightforward and preferred for posteriorly located SS, it may be insufficient for accessing anterior or anterolateral neoplasms; furthermore, this method does not allow access to extraforaminal pathologies. Utilizing a far lateral approach for dumbbell C2 schwannomas presents several benefits, such as reducing spinal cord retraction, enhancing visualization of the anterior brain stem, facilitating access to intra- and extradural tumors, providing early control of the VA, and allowing for an extension of the approach in various ways based on the procedural requirements.[ 2 , 9 , 13 , 18 , 29 ]

The far lateral approach usually involves a suboccipital craniectomy or craniotomy, requiring at least the removal of the C1 hemilamina and early identification of VA through dissection of the suboccipital triangle.[ 31 ] Mobilization of the nuchal muscles can be performed in layers or through a single subperiosteal block.[ 14 , 16 , 31 ] However, we prefer subperiosteal dissection because it presents advantages such as reduced time, less bleeding, and minimal manipulation that could lead to increased postoperative pain and muscle atrophy. The basic lateral approach, without drilling the occipital condyle, may be all that is necessary to access lesions located in the CVJ. It also lays the groundwork for performing transcondylar, supracondylar, and paracondylar approaches to provide better exposure based on necessity.[ 2 , 13 , 22 ]

Using this procedure, an overall improvement in symptoms was observed in 85.7% of the cases in this series. There were no significant surgical complications, and no tumor recurrence was detected during the average follow-up period of 21.4 months (range 1–54). The mean mJOA score increased from a preoperative 10.7 (range 3–15) to a postoperative score of 17 (range 13–18).

Surgical pearls

The far lateral approach has been adopted for the resection of tumors located in the upper cervical spinal cord and is suitable for resection of dumbbell C2 schwannomas. This approach demands a thorough understanding of anatomy and careful surgical technique to maximize tumor resection while minimizing complications, particularly to the surrounding neural and vascular structures. Therefore, important considerations must be considered:

(A) Detachment of nuchal muscles: Subperiosteal detachment of the nuchal muscles is performed to skeletonize the suboccipital region, the posterior tip of the occipital condyle, the posterior arch of C1, and, when necessary, the spinous process of C2. (B) Suboccipital craniotomy/craniectomy: While not always required, if performed, a small bone flap is generally sufficient. If occipitocervical fixation is necessary (though usually not needed), the craniotomy/craniectomy should be conducted as laterally as possible to preserve as much of the occipital squama as feasible, thereby ensuring that the instrumentation is not compromised. (C) Resection of C1 and C2: A hemilaminectomy of C1 is performed by crossing slightly over the midline; in some cases, a C2 hemi-semi-laminectomy may be required to enhance exposure. (D) Preservation of joint facets: the joint facets must always be preserved, allowing instability only from the tumor itself. (E) VA preservation: the third segment of the VA must be identified and preserved, necessitating careful dissection and attention to the artery’s anatomy to avoid injury, which could lead to significant neurological deficits. (F) Dural opening: the dura is opened with a laterally based curvilinear incision, which is then reflected with multiple sutures to broaden the surgical field. (G) Tumor resection strategy: if the intradural component is predominant, it should be removed first to identify cranial nerve XI and the fourth segment of the VA. If the extradural component is larger, it should be excised before the dural opening. The VA is frequently displaced superiorly by the tumor. To reduce the risk of vascular injury, the initial resection should commence at the inferior pole of the tumor and proceed in a ventral to dorsal direction.

CONCLUSION

Dumbbell schwannomas of C2 pose a surgical challenge due to their complex location at the CVJ. The far lateral approach is a versatile technique for accessing and resecting tumors with dumbbell characteristics, particularly those situated in a ventrolateral position. In addition, it offers several advantages by minimizing the retraction of adjacent neurovascular structures, providing a broad surgical field to access both intra- and extradural lesions, and facilitating the GTR of these tumors with favorable outcomes.

Ethical approval

The Local Health Research Committee approved the research/study at Hospital de Especialidades del Centro Médico Nacional Siglo XXI, number F-2024-3601-258, dated November 2024.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript, and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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