Operability score: An innovative tool for quantitative assessment of operability in comparative studies on surgical anatomy

Comparative Analysis on Surgical Operability and Degree of Exposure of Microsurgical Approaches to Intraforaminal Lumbar Disk Herniations

BACKGROUND

 Intraforaminal lumbar disk herniations (IFDHs) represent a heterogeneous and relatively uncommon disease; their treatment is technically demanding due to the anatomical relationships with nerve roots and vertebral joints. Over time, several approaches have been developed without reaching a consensus about the best treatment strategy.

MATERIALS AND METHODS

 Authors comparatively analyze surgical operability and exposure in terms of quantitative variables between the different microsurgical approaches to IFDHs, defining the impact of each approach on surgical maneuverability and exposure on specific targets.A comparative microanatomical laboratory investigation was conducted. The operability score (OS) was applied for quantitative analysis of surgical operability.

RESULTS

 Transarticular and combined translaminar-trans-pars-interarticularis approaches result in providing the best surgical exposure and maneuverability on all targets with surgical controls on both nerve roots, at the expense of a higher risk of iatrogenic instability. Trans-pars-interarticularis approach reaches comparable levels of operability, even limited to the pure foraminal area (lateral compartment); similar findings were recorded for partial facetectomy on the medial compartment. The contralateral interlaminar approach provides good visualization of the foramen without consensual favorable maneuverability, which should be considered the main drawback.

CONCLUSIONS

 Approach selection has to consider disease location, the possible migration of disk fragments, the degree of nerve root involvement, and risk of iatrogenic instability. According to the findings, authors propose an operative algorithm to tailor the surgical strategy, based both on the precise definition of anatomic boundaries of exposure of each approach and on surgical maneuverability on specific targets.

The carotid sheath route: An option to approach retrocarotid prespinal tumors with paravertebral extension

Background

The elective route to approach paravertebral lesions growing into the anterolateral lodge of the neck is widely recognized as the prespinal route with its two major variants. Recently, attention has been focused on the possibility of opening the inter-carotid-jugular window in case of reparative surgery for traumatic brachial plexus injury.

Aims

For the first time, the authors validate the clinical application of the carotid sheath route in the surgical treatment of paravertebral lesions expanding into the anterolateral lodge of the neck.

Methods

A microanatomic study was conducted to collect anthropometric measurements. The technique was illustrated in a clinical setting.

Results

The opening of the inter-carotid-jugular surgical window allows additional access to the prevertebral and periforaminal space. It optimizes the operability on the prevertebral compartment, compared to the retro-sternocleidomastoid (SCM) approach, and on the periforaminal compartment, compared to the standard pre-SCM approach. The surgical control of the vertebral artery is comparable to that obtained with the retro-SCM approach, while the control of the esophagotracheal complex and the retroesophageal space is comparable to the pre-SCM approach. The risk profile on the inferior thyroid vessels, recurrent nerve, and sympathetic chain is superimposable to the pre-SCM approach.

Conclusions

The carotid sheath route is a safe and effective option to approach prespinal lesions with retrocarotid monolateral paravertebral extension.

Impact of C-shaped skin incision on surgical operability in the retrosigmoid approach: when a good start is half of the job

BACKGROUND

The retrosigmoid approach (RSA) is one of the routes of choice to approach tumors and vascular lesions of the cerebellopontine angle. Among different types of skin incisions and soft tissue dissection techniques, the most widely used variants comprise the straight/lazy S-shaped and the C-shaped incisions. Several reports discuss advantages in terms of functional and clinical outcomes of the C-shaped incision, but scientific considerations about the critical impact of this kind of incision on surgical operability are still extremely limited.

OBJECT

Authors comparatively analyze the advantage provided by C-shaped incision in RSA in terms of anatomic exposure and surgical operability, compared with straight/lazy S-shaped one.

METHODS

A comparative microanatomical laboratory investigation was conducted. The operability score (OS) was applied for quantitative analysis of surgical operability.

RESULTS

C-shaped incision, providing a significant reduction of the overall working distance (-13%) together with an overall increase of the maneuverability area (+ 204.9%), did improve the conizing effect on the surgical corridor. It optimized overall maneuverability of surgical instruments, in terms of angle of attack (+ 27.7%), as well as maneuverability arc (+ 122%), on the entire surgical field. C-shaped incision ensured good operability on all surgical targets (OS ranging from 2 to 3), most significantly improving surgical maneuverability at the porus trigeminus and internal acoustic meatus.

CONCLUSION

C-shaped incision in the RSA significantly improves anatomic exposure and surgical operability as compared with straight/lazy S-shaped incision.

Comparative Anatomical Study of Fronto-Orbito-Zygomatic and Fronto-Temporal Approach to the Central Skull Base

ABSTRACT

Despite the advances in microsurgery and neuroanatomy, surgery of the central skull base still represents a challenge. Fronto-temporal approach has represented the mainstay of surgical approaches to this region. With advances in skull base surgery, orbital and zygomatic extensions were added to fronto-temporal approach to improve exposure minimizing brain retraction.The authors compared fronto-temporal and fronto-orbitozygomatic approaches to the central skull base by using the previously described operability score, to three different anatomical targets: the ipsilateral anterior clinoid process, the contralateral anterior clinoid process, and the ipsilateral posterior clinoid process.Based on the measurements taken, fronto-orbitozygomatic approache showed higher values at all 3 targets. The reported values were critically discussed.The operability score has been reported as an effective method to compare surgical approaches. The present study demonstrated the maximal possibility of exposure of the two approaches. Based on the strong variability of this anatomical region, especially because of the different pathologies, the authors suggest considering the operability score as a further tool to better define the best surgical approach to this anatomical region.

Endoscope-Assisted Neuroportal Transcerebellar Approach to the Fourth Ventricle: An Anatomical Study

BACKGROUND AND STUDY AIMS

 Minimally invasive approaches to deep-seated lesions still represent a fundamental issue in modern neurosurgery. Tubular retractors allow to enhance the operability of intraventricular lesions, minimizing the risk of damages to brain parenchyma. Increasing interest for portal devices has been mainly focused on supratentorial pathologies, while transportal approaches in the posterior cranial fossa have been rarely described. In the present study, the authors aimed to investigate the surgical exposure and operability obtained with a microsurgical neuroportal transcerebellar approach targeting the fourth ventricle, assisted by endoscopic exploration.

MATERIAL AND METHODS

 Six cadaveric specimens were provided for anatomical microsurgical dissection and Vycor ViewSite Brain Access System was used as tubular retractor. Surgical feasibility of the neuroportal transcerebellar approach was demonstrated through a definable and measurable parameter, the operability score.

RESULTS

 The neuroport provided a surgical corridor away from eloquent structures to target the whole fourth ventricle cavity, preventing injury to cerebellar nuclei and white matter pathways and, potentially, minimizing the risk of surgical morbidity. Maximal operability was reached in the pontomedullary junction and medullary area of the ventricular floor. Transportal endoscopic assistance contributed to a further extension of surgical exposure in blind spots, corresponding to the ipsilateral lateral recess, the uppermost part of the fourth ventricle, and the obex.

CONCLUSION

 The neuroportal transcerebellar approach represents a viable alternative route to the fourth ventricle, avoiding vermian splitting or subarachnoid dissection of the cerebellomedullary cistern. Endoscopic assistance enhances the exposure of the surgical field and accomplishes a valid instrument for intraventricular orientation to ease microsurgical procedures.

Combined, Rib-Sparing, Bilateral Approach to the Ventral Mid and Low Thoracic Spine: Study on Comparative Anatomy and Surgical Feasibility

BACKGROUND

Pathologies of the ventral thoracic spine represent a challenge, igniting arguments about which should be the ideal surgical approach to access this area. Anterior transthoracic thoracotomy and a number of posterolateral routes have been developed. Among the latter, costotransversectomy has demonstrated to provide good ventral exposure with a lower, but not negligible, morbidity. The optimal approach should be the one minimizing surgical morbidity on both neural and extraneural structures while optimizing exposure.

METHODS

The authors described the combined, rib-sparing, bilateral approach (CRBA) to the ventral mid/low-thoracic spine. The technique combines a transfacet pedicle partially sparing approach on one side and a transpedicular with transverse process resection on the contralateral one. A laboratory investigation was conducted. The technique was applied in a surgical setting, and a case was reported.

RESULTS

CRBA is rib-sparing, completely extracavitary, and does not require pleural exposure and paraspinal muscle splitting, thus minimizing potential morbidity. The combination of 2 corridors ensures the greatest exposure compared with standard posterolateral approaches. The only blind corner is limited to a small area just in front of the dural sac. A bimanual approach optimizes control during surgical manipulation, even if the area of maneuverability and cross-section areas of surgical corridors are slightly limited compared to traditional costotransversectomy due to the minimally invasive nature of the procedure.

CONCLUSIONS

CRBA represents a safe and effective option to access the ventral mid/low thoracic spine. It provides great exposure and bimanual manipulation of the surgical target, minimizes potential morbidity, and avoids entrance into the thoracic cavity and paraspinal muscle splitting.

Temporal Galeofascial Flap for Reconstruction After Transmaxillary Approaches to the Clival Region

BACKGROUND

A paramount concern after transmaxillary approaches has been skull base reconstruction. Regional pedicled flaps represent the best reconstructive option. We have described a technique to harvest a lateral-based multilayered vascularized flap for skull base reconstruction after resection of large tumors using the transmaxillary transpterygoid approach (TMTPA).

METHODS

We performed a cadaver study using the TMTPA to harvest the combined temporal galeofascial flap (CTGF). The first layer, with major sealing capabilities, is composed by a temporoparietal galeal-pericranial flap. The second layer is composed by temporal muscle fascia to provide mechanical support for flap dural engrafting.

RESULTS

The CTGF provides excellent coverage of both the clival dural lining and the ipsilateral pterygopalatine fossa structures (×1.6). The CTGF is pliable and easy to harvest. It offers great flexibility in flap content and design, providing a large quantity of vascularized tissue. The vascular pedicle derives from the superficial temporal vessels, which can ensure flap trophism.

CONCLUSIONS

CTGF represents an effective option as a regional multilayered pedicled flap for skull base reconstruction after resection of clival tumors using the TMTPA. The flap pedicle, owing to its anatomical location, will often be preserved even after repeated microsurgical or endoscopic procedures, providing a technical alternative for reconstruction even in patients who have undergone multiple surgeries with low residual availability of regional flaps.

Temporal myofascial segmentation for multilayer reconstruction of middle cranial fossa floor after extradural subtemporal approach to the clival and paraclival region

BACKGROUND

Skull-base reconstruction represents a concern after resection of middle fossa (MF) tumors by the extradural subtemporal transzygomatic approach (ESTZ). Regional pedicled flaps appear to be the best option. This study describes a technique for temporal myofascial segmentation to harvest a multilayered vascularized flap for MF reconstruction, which might preserve temporal muscle (TM) function and its blood supply.

METHODS

The technique to harvest a combined segmented temporal myofascial flap (CSTMF) is described. The flap consists in a temporal fascial (TFF) and a muscle flap (TMF), composed by TM anterior-medial bundle (AMB).

RESULTS

CSTMF provides wide coverage of dural lining, through the TFF, and of dead-space, through the TMF. The possibility to tailor TMF according to the need, anatomically preserving the blood supply, enables to significantly increase its volume.

CONCLUSION

CSTMF represents an effective option as regional multilayered pedicled flap for MF reconstruction, potentially preserving TM function and minimizing the cosmetic impact.

Contralateral Transfalcine Versus Ipsilateral Anterior Interhemispheric Approach for Midline Arteriovenous Malformations: Surgical and Anatomical Assessment

BACKGROUND

The contralateral anterior interhemispheric approach (CAIA) is considered to provide surgical advantages to access deep midline lesions: wider working angle, gravity enhanced dissection and retraction, more efficient lighting, and ergonomics. Our team has previously published on the merits of using a contralateral trajectory for medial frontoparietal arteriovenous malformations (AVMs) compared with the conventional anterior interhemispheric approach (IAIA). In this article, we compare the IAIA and CAIA for the resection of medial frontoparietal AVMs using quantitative surgical and anatomical analysis.

METHODS

Two models were designed mimicking the most common features of midline AVMs. The CAIA and IAIA were performed bilaterally in 10 specimens. Variables to compare technical feasibility (surgical window [SW] and surgical freedom [SF], target exposure, and angle of attack) were independently assessed using stereotactic navigation. The average SW, SF, and angle of attack were compared with the Student t test. Significance threshold was set at 0.05.

RESULTS

The CITA and IAIA were similar in terms of SW, target exposure, and SF in the superior aspect of the AVM. In the depth of the interhemispheric fissure, the CAIA was significantly superior to IAIA in both AVM models: 77% wider AA for the inferior aspect of the AVM (P < 0.01) and greater SF for the draining vein (54%, P = 0.01), ipsilateral (98%, P = 0.02), and contralateral ACA (117%, P < 0.01).

CONCLUSIONS

This study suggests technical superiority of the CAIA for the resection of deep midline AVMs. No objective difference was noted in the superficial areas of our models, denoting that IAIA is a safer choice for superficial AVMs. Our results set the foundation for further clinical analysis comparing both approaches.

The paramedian supracerebellar transtentorial approach to the posterior fusiform gyrus

BACKGROUND

The posterior fusiform gyrus lies in a surgically challenging region. Several approaches have been described to access this anatomical area. The paramedian supracerebellar transtentorial (SCTT) approach benefits from minimal disruption of normal neurovascular tissue. The aim of this study was to demonstrate its application to access the posterior fusiform gyrus.

METHODS

Three brains and six cadaveric heads were examined. A stepwise dissection of the SCTT approach to the posterior fusiform gyrus was performed. Local cortical anatomy was studied. The operability score was applied for comparative analysis on surgical anatomy.

RESULTS

The major posterior landmark used to identify the fusiform gyrus with respect to the medial occipitotemporal gyrus was the collateral sulcus, which commonly bifurcated at its caudal extent. Compared with other surgical approaches addressed to access the region, SCTT demonstrated the best operability in terms of maneuverability arc. Favorable tentorial anatomy is the only limiting factor.

CONCLUSIONS

The supracerebellar transtentorial approach is able to provide access to the posterior fusiform gyrus via a minimally disruptive, anatomic, microsurgical corridor.