Volume of Surgical Freedom: The Most Applicable Anatomical Measurement for Surgical Assessment and 3-Dimensional Modeling

Quantitative Analysis of the Supraorbital, Transorbital Microscopic, and Transorbital Neuroendoscopic Approaches to the Anterior Skull Base and Paramedian Vasculature

Objectives  Our objective was to compare transorbital neuroendoscopic surgery (TONES) with open craniotomy and analyze the effect of visualization technology on surgical freedom. Design  Anatomic dissections included supraorbital craniotomy (SOC), transorbital microscopic surgery (TMS), and TONES. Setting  The study was performed in a neurosurgical anatomy laboratory. Participants  Neurosurgeons dissecting cadaveric specimens were included in the study. Main Outcome Measures  Morphometric analysis of cranial nerve (CN) accessible lengths, frontal lobe base area of exposure, and craniocaudal and mediolateral angle of attack and volume of surgical freedom (VSF) of the paraclinoid internal carotid artery (ICA), terminal ICA, and anterior communicating artery (ACoA). Results  The mean (standard deviation [SD]) frontal lobe base parenchymal exposures for SOC, TMS, and TONES were 955.4 (261.7) mm 2 , 846.2 (249.9) mm 2 , and 944.7 (158.8) mm 2 , respectively. Access to distal vasculature was hindered when using TMS and TONES. Multivariate analysis estimated that accessing the paraclinoid ICA with SOC would provide an 11.2- mm 3 increase in normalized volume (NV) compared with transorbital corridors ( p  < 0.001). There was no difference between the three approaches for ipsilateral terminal ICA VSF ( p  = 0.71). Compared with TONES, TMS provided more access to the terminal ICA. For the ACoA, SOC produced the greatest access corridor maneuverability (mean [SD] NV: 15.6 [5.6] mm 3 for SOC, 13.7 [4.4] mm 3 for TMS, and 7.2 [3.5] mm 3 for TONES; p  = 0.01). Conclusion  SOC provides superior surgical freedom for targets that require more lateral maneuverability, but the transorbital corridor is an option for accessing the frontal lobe base and terminal ICA. Instrument freedom differs quantifiably between the microscope and endoscope. A combined visualization strategy is optimal for the transorbital corridor.

Volume of Operative Maneuverability as a New Measurement in Neuroanatomical Research: A Methodological Quantitative Study and Translational Use in the Operating Room

OBJECTIVE

The lack of standardized metrics in neuroanatomical research limits the objective assessment of neurosurgical approaches. We introduce a novel volume-based parameter, the Volume of Operative Maneuverability (VOM), and evaluate its utility in quantifying surgical corridor dimensions.

METHODS

Seven microscopic and endoscopic skull base approaches were performed on 4 embalmed latex-injected human cadaveric specimens. A spatial principal component analysis algorithm converted surgical entry and target areas into ellipses, allowing ellipsoidal-based VOM calculations. Corridor length ("target distance") and a fixed 10 mm distance from the target ("standardized VOM" [sVOM]) were also measured. Feasibility and reproducibility were assessed using three-dimensional photogrammetry, preoperative imaging models, and a clinical case.

RESULTS

Endoscopic endonasal and anterior transmaxillary approaches offered sufficient corridor volume and trajectory distance but created longer, narrower surgical corridors with lower sVOM than transcranial approaches. Conversely, pretemporal-orbitozygomatic and subtemporal corridors showed the highest VOM and sVOM. Illustrative examples confirmed consistent measurement in photogrammetry and preoperative imaging. A clinical case involving a right spheno-cavernous meningioma demonstrated a VOM of 2.328 cm³, sVOM of 0.615 cm³, and a target distance of 18 mm during extradural anterior clinoidectomy.

CONCLUSIONS

VOM provides a quantitative, reproducible metric for assessing surgical maneuverability toward irregular target surfaces, overcoming the limitations of traditional qualitative assessments. Preliminary data support its use in quantitative neuroanatomical research and suggest potential integration into surgical planning and intraoperative data collection.

Biportal Endoscopic TransOrbital and transMaxillary Approach to the Cranio-Orbital Region and Middle Cranial Fossa: A Preliminary Analysis of Maneuverability

BACKGROUND AND OBJECTIVES

Traditional and well-established transcranial approaches to the spheno-orbital region and middle cranial fossa guarantee optimal intracranial exposure, and additional orbital and zygomatic osteotomies provide further control over extracranial components to be resected; however, these techniques come at the cost of additional morbidity. The introduction of minimally invasive endoscopic approaches and the conceptualization of the so-called "multiportal" paradigm might provide an alternative route. This preliminary study investigates the feasibility of the combined Biportal Endoscopic TransOrbital and transMaxillary Approach (bETOMA) approach to the spheno-orbital and middle cranial fossa regions.

METHODS

Using 4 silicon-injected adult cadaver heads (8 sides; 16 approaches), we systematically dissected through superior eyelid ETOA and endoscopic TMA approaches. The analysis focused on pterygopalatine, infratemporal, anterior and middle cranial fossae, Meckel cave, and cavernous sinus access. We evaluated the feasibility of bETOMA using linear distances, angles of attack, and exposure areas. We also introduced volume of operative maneuverability, its standardized derivative (sVOM), target distance, visuo-operative angle, and working zone volume as novel metrics.

RESULTS

The analysis revealed comparable angles of attack between approaches. ETOA and TMA exposure areas were 918.38 ± 223.93 mm 2 and 257.07 ± 86.07 mm 2 , respectively. TMA showed a larger VOM in the greater sphenoid wing, but ETOA offered superior distal maneuverability (sVOM: 5.39 ± 1.94 vs 2.54 ± 0.79 cm 3 ) and closer intracranial space access (27.45 vs 50.83 mm). The combined approaches yielded a mean working zone volume of 13.75 ± 3.73 cm 3 in the spheno-orbital interface.

CONCLUSION

The bETOMA approach provides adequate neurovascular exposure and maneuverability to the spheno-orbital region, infratemporal, and anterior and middle cranial fossae, addressing significant limitations of previously investigated monoportal techniques (ie, optic nerve decompression, hyperostotic bone resection, and infratemporal exposure). This combined minimally invasive approach might help manage lesions harbored within the cranio-orbital interface region invading the extracranial space.

Improving the metric of surgical freedom in the laboratory based on a novel concept of volume

BACKGROUND

In laboratory-based neuroanatomical studies, surgical freedom, the most important metric of instrument maneuverability, has been based on Heron's formula. Inaccuracies and limitations hinder this study design's applicability. A new methodology, volume of surgical freedom (VSF), may produce a more realistic qualitative and quantitative representation of a surgical corridor.

METHODS

Overall, 297 data set measurements assessing surgical freedom were completed for cadaveric brain neurosurgical approach dissections. Heron's formula and VSF were calculated specifically to different surgical anatomical targets. Quantitative accuracy and the results of an analysis of human error were compared.

RESULTS

Heron's formula for irregularly shaped surgical corridors resulted in overestimation of the respective areas (minimum overestimation 31.3%). In 92% (188/204) of data sets reviewed for influence of offset, areas calculated on the basis of measured data points were larger than areas calculated on the basis of the translated best-fit plane points (mean [SD] overestimation of 2.14% [2.62%]). Variability in the probe length attributable to human error was small (mean [SD] calculated probe length 190.26 mm [5.57 mm]).

CONCLUSIONS

VSF is an innovative concept that can develop a model of a surgical corridor producing better assessment and prediction of the ability to maneuver and manipulate surgical instruments. VSF corrects for deficits in Heron's method by generating the correct area for an irregular shape using the shoelace formula, adjusting the data points to account for offset, and attempting to correct for human error. VSF produces 3-dimensional models and, therefore, is a preferable standard for assessing surgical freedom.

Morphometric Comparison of Endoscopic Endonasal Transpterygoid and Precaruncular Contralateral Medial Transorbital Approaches to Sphenoid Sinus Lateral Recess

BACKGROUND AND OBJECTIVES

The endoscopic endonasal transpterygoid approach (TPA), minimally invasive compared with the sublabial transmaxillary and transcranial approaches, still accounts for morbidity in benign lateral recess of sphenoid sinus (LRSS) pathologies. Others have suggested an alternative route to the LRSS, the endoscopic contralateral medial transorbital approach (cMTO). However, no quantitative evidence exists to support the clinical application of this approach. This cadaveric study, in a controlled laboratory setting, provides a morphometric comparison of the TPA and cMTO for accessing the LRSS. The study also details the anatomy and technical nuances for optimizing the cMTO corridor.

METHODS

Ten fresh preinjected human cadaveric specimens (20 sides) were dissected with neuronavigation, completing endoscopic cMTO and TPA on each side. Four parameters-working distance to lateral recess, surgical exposure area, angle of attack (AoA), and surgical freedom-were measured for each approach. Relevant osteological measurements in 10 dried human skulls were recorded.

RESULTS

The mean distance from the superior margin of the lacrimal sac impression to the inferior margin of the trochlear fossa was 10.29 ± 1.13 mm, and that from the anterior ethmoidal artery foramina to the posterior lacrimal crest was 9.63 ± 1.23 mm. The mean exposure area around the LRSS was significantly higher in TPA (614.09 ± 40.38 mm 2 ) than in cMTO (391.19 ± 59.01 mm 2 , P = .001). The mean AoA was 9.83° and 10.24° in the cMTO and TPA, respectively, in the craniocaudal direction ( P = .529). In the horizontal plane, it was 9.29° and 10.76° ( P = .012). There was no significant difference in surgical freedom between the cMTO and TPA (804.61 and 806.05 mm 3 , respectively; P = .993).

CONCLUSION

Although comparatively limited exposure area, the cMTO approach has a similar AoA and surgical freedom as TPA and offers better visualization and ergonomic advantages. cMTO provides a feasible, less morbid, multiport technique for benign sphenoid sinus lateral recess pathologies.

Toward "bigger" data for neurosurgical anatomical research: a single centralized quantitative neurosurgical anatomy platform

Quantitative neurosurgical anatomy research aims to produce surgically applicable knowledge for improving operative decision-making using measurements from anatomical dissection and tools such as stereotaxis. Although such studies attempt to answer similar research questions, there is little standardization between them, offering minimal comparability. Modern technology has been incorporated into the research methodology, but many scientific principles are lacking, and results are not broadly applicable or suitable for evaluating big-data trends. Advances in information technology and the concept of big data permit more accessible and robust means of producing valuable, standardized, reliable research. A technology project, "Inchin," is presented to address these needs for neurosurgical anatomy research. This study applies the concept of big data to neurosurgical anatomy research, specifically in quantifying surgical metrics. A remote-hosted web application was developed for computing standard neurosurgical metrics and storing measurement data. An online portal (Inchin) was developed to produce a database to facilitate and promote neurosurgical anatomical research, applying optimal scientific methodology and big-data principles to this recent and evolving field of research. Individual data sets are not insignificant, but a collective of data sets present advantages. Large data sets allow confidence in data trends that are usually obscured in smaller numbers of samples. Inchin, a single centralized software platform, can act as a global database of results of neurosurgical anatomy studies. A calculation tool ensuring standardized peer-reviewed methodology, Inchin is applied to the analysis of neurosurgical metrics and may promote efficient study collaboration within and among neurosurgical laboratories.

Extradural anterior clinoidectomy versus endoscopic transplanum-transcavernous approach to the paraclinoid region: quantitative anatomical exposure analysis

BACKGROUND

Transcranial anterior clinoidectomy is a conventional microsurgical approach for treatment of paraclinoid aneurysms. The endoscopic endonasal approach (EEA) is an alternative method for clipping intracranial aneurysms. No analysis has been conducted to anatomically compare approaches with respect to treating paraclinoid aneurysms. The surgical anatomical exposures of the paraclinoid region during transcranial extradural anterior clinoidectomy (EAC) and the endoscopic endonasal transplanum-cavernous approach (EETC) are described and quantitatively assessed.

METHOD

Seven cadaveric heads underwent EAC and EETC. Measurements included the area of exposure, volume of surgical freedom, angle of attack, ophthalmic artery (OphA) origin, and coronal exposure angle of the internal carotid artery (ICA).

RESULTS

The EETC provided a larger area of exposure than the EAC (100.1±24.9 vs 76.1±12.9 mm², p = 0.04). The EAC provided a higher volume of surgical freedom and greater angle of attack than the EETC in all neurovascular parameters, including the OphA, superior hypophyseal artery (SHA), distal ICA, and distal dural ring (all p < 0.001). The OphA origin was intradural in 85.7% and extradural in 14.3% of specimens. With regard to the coronal angle of exposure, the EAC exposed the OphA and SHA in the upper lateral quadrant (67.9±7.8° and 80.6±4.5°, respectively) and the distal ICA in the upper medial and upper lateral quadrants (92±7.5°). The EEA exposed the OphA, SHA, and distal ICA in the upper medial and lower medial quadrants (130.4±10.7°, 68.4±10.8°, and 58±11.4°, respectively).

CONCLUSIONS

The EAC and EETC each offer specific advantages for paraclinoid region exposure. The EAC is appropriate for paraclinoid aneurysms that occur at the dorsolateral surface of the paraclinoid ICA. The EETC is an alternative approach for aneurysms that occur along medial surface of the paraclinoid ICA (e.g., carotid cave and SHA aneurysms). The EETC provides greater surgical exposure to the medial aspect of the paraclinoid ICA.

Volumetric 3-Dimensional Analysis of the Supraorbital vs Pterional Approach to Paramedian Vascular Structures: Comprehensive Assessment of Surgical Maneuverability

BACKGROUND

Both the pterional and supraorbital approaches have been proposed as optimal access corridors to deep and paramedian anatomy.

OBJECTIVE

To assess key intracranial structures accessed through the surgical approaches using the angle of attack (AOA) and the volume of surgical freedom (VSF) methodologies.

METHODS

Ten pterional and 10 supraorbital craniotomies were completed. Data points were measured using a neuronavigation system. A comparative analysis of the craniocaudal AOA, mediolateral AOA, and VSF of the ipsilateral paraclinoid internal carotid artery (ICA), terminal ICA, and anterior communicating artery (ACoA) complex was completed.

RESULTS

For the paraclinoid ICA, the pterional approach produced larger craniocaudal AOA, mediolateral AOA, and VSF than the supraorbital approach (28.06° vs 10.52°, 33.76° vs 23.95°, and 68.73 vs 22.59 mm3 normalized unit [NU], respectively; P < .001). The terminal ICA showed similar superiority of the pterional approach in all quantitative parameters (27.43° vs 11.65°, 30.62° vs 25.31°, and 57.41 vs 17.36 mm3 NU; P < .05). For the ACoA, there were statistically significant differences between the results obtained using the pterional and supraorbital approaches (18.45° vs 10.11°, 29.68° vs 21.01°, and 26.81 vs 16.53 mm3 NU; P < .005).

CONCLUSION

The pterional craniotomy was significantly superior in all instrument maneuverability parameters for approaching the ipsilateral paraclinoid ICA, terminal ICA, and ACoA. This global evaluation of 2-dimensional and 3-dimensional surgical freedom and instrument maneuverability by amalgamating the craniocaudal AOA, mediolateral AOA, and VSF produces a comprehensive assessment while generating spatially and anatomically accurate corridor models that provide improved visual depiction for preoperative planning and surgical decision-making.