The historical evolution of microvascular decompression for trigeminal neuralgia: from Dandy's discovery to Jannetta's legacy.

Although the symptoms of trigeminal neuralgia (TN) have been well described throughout the history of medicine, its etiology was initially not well understood by most surgeons. The standard procedure used to treat TN today, microvascular decompression (MVD), evolved due to the efforts of numerous neurosurgeons throughout the twentieth century. Walter Dandy was the first to utilize the cerebellar (suboccipital) approach to expose the trigeminal nerve for partial sectioning. He made unique observations about the compression of the trigeminal nerve by nearby structures, such as vasculature and tumors, in TN patients. In the 1920s, Dandy unintentionally performed the first MVD of the trigeminal nerve root. In the 1950s, Palle Taarnhøj treated a TN patient by performing the first intentional decompressive procedure on the trigeminal nerve root solely through the removal of a compressive tumor. By the 1960s, W. James Gardner was demonstrating that the removal of offending lesion(s) or decompression of nearby vasculature alleviated pressure on the trigeminal nerve and the pain associated with TN. By the 1990s, Peter Jannetta proved Dandy's original hypothesis; he visualized the compression of the trigeminal nerve at the root entry zone in TN patients using an intraoperative microscope. In this paper, we recount the historical evolution of MVD for the treatment of TN.

Extended Anterior Petrosectomy Through the Transcranial Middle Fossa Approach and Extended Endoscopic Transsphenoidal-Transclival Approach: Qualitative and Quantitative Anatomic Analysis.

BACKGROUND: Petroclival tumors and ventrolateral lesions of the pons present unique surgical challenges. This cadaveric study provides qualitative and quantitative anatomic comparison for an anterior petrous apicectomy through the transcranial middle fossa (TMF) and expanded endoscopic transsphenoidal-transclival approaches. METHODS: In 10 silicone-injected heads, the petrous apex and clivus were drilled extradurally using middle fossa and endonasal approaches. With in situ and frameless stereotactic navigation, we defined consistent points to compare working areas, bone removal volumes, approach angles, and surgical freedom. RESULTS: Mean exposed TMF area (21.03 ± 3.46 cm2) achieved a 44.71 ± 4.13° working angle to the brainstem between cranial nerves V and VI. Kawase's rhomboid area measured 1.76 ± 0.34 cm2, and bone removal averaged 1.20 ± 0.12 cm3 at the petrous apex. Surgical freedom on the lateral brainstem was higher halfway between cranial nerves V and VI at the center of the rhomboid compared with midline at the basilar sulcus (P < 0.01). After clivectomy and petrous apicectomy, mean exposed expanded endoscopic transsphenoidal-transclival area was 5.29 ± 0.66 cm2. Approach from either nostril showed no statistically significant differences in surgical freedom at the foramen lacerum and midpoint basilar sulcus. At the petrous apex, bone volume removed and area exposed were significantly larger for the TMF approach (P < 0.001). CONCLUSIONS: Expanded transclival anterior petrosectomy through the TMF approach provides an adequate corridor to lesions in the upper ventrolateral pons. The expanded endoscopic transsphenoidal-transclival approach better fits midline lesions not extending laterally beyond cranial nerve VI and C3 carotid when evaluating normal anatomic parameters.

Comprehensive anatomy of the foramen ovale critical to percutaneous stereotactic radiofrequency rhizotomy: cadaveric study of dry skulls.

OBJECTIVE: Percutaneous stereotactic radiofrequency rhizotomy (PSR) is often used to treat trigeminal neuralgia, a serious condition that results in lancinating, episodic facial pain. Thorough understanding of the microsurgical anatomy of the foramen ovale (FO) and its surrounding structures is required for efficient, effective, and safe use of this technique. This morphometric study compares anatomical and surgical orientations to identify the variations of the FO and assess cannulation difficulty. METHODS: Bilateral foramina from 174 adult human dry skulls (348 foramina) were analyzed using anatomical and surgical orientations in photographs from standardized projections. Measurements were obtained for shape, size, adjacent structures, and morphometric variability effect on cannulation. The risk of potential injury to surrounding structures was also assessed. RESULTS: The authors identified 6 distinctive shapes of the FO and 5 anomalous variants from the anatomical view, and 6 shapes from the surgical view. In measurements of surface area of this foramen obtained using the surgical view, loss (average 18.5% ± 5.7%) was significant compared with the anatomical view. Morphometrically, foramen size varied significantly and obstruction from a calcified pterygoalar ligament occurred in 7.8% of specimens. Importantly, 8% of foramina were difficult to cannulate, thus posing a 12% risk of inadvertent cannulation of the foramen lacerum. CONCLUSIONS: Significant variability in the FO's shape and size probably affected its safe and effective cannulation. Preoperative imaging by 3D head CT may be helpful in predicting ease of cannulation and in guiding treatment decisions, such as a percutaneous approach over microvascular decompression or radiosurgery.

Supraorbital vs Endo-Orbital Routes to the Lateral Skull Base: A Quantitative and Qualitative Anatomic Study.

BACKGROUND: Various extensions of the supraorbital approach reach the lateral and parasellar middle cranial fossa regions by removing the orbital rim and greater/lesser sphenoid wings. Recent proposals of a purely endoscopic ventral transorbital pathway to these regions heighten the need to compare these surgical windows. OBJECTIVE: To detail the lateral and parasellar middle cranial fossa regions and quantify exposures by 2 surgical windows (transcranial and transorbital) through anatomic study. METHODS: In 5 cadaveric specimens (10 sides), dissections consisted of 3 stages: stage 1 began with the supraorbital approach via the eyebrow; stage 2, endo-orbital approach via the superior eyelid, continued with removal of lesser and greater sphenoid wings; and stage 3, extended supraorbital, re-evaluated the gains of stage 2 from the perspective of stage 1. Operative working areas were quantified in Sylvian, anterolateral temporal, and parasellar regions; bone removal volumes were measured at each stage (nonpaired Student t-test). RESULTS: Visualization into the anterolateral temporal and Sylvian areas, though varied in perspective, were comparable with either eyelid or transcranial routes. Compared with transcranial views through a supraorbital window, the eyelid approach significantly increased exposure in the parasellar region with wider angle of attack (P < .01) and achieved comparable bone removal volumes. CONCLUSION: Stage 2's unique anatomic view of the lateral and parasellar middle cranial fossa regions paves the way for possible surgical application to select pathologies typically treated via transcranial approaches. Disadvantages may be the surgeon's unfamiliarity with the anatomy of this purely endoscopic, ventral route and difficulties of dural and orbital repair.

Paratrigeminal, Paraclival, Precavernous, or All of the Above? A Circumferential Anatomical Study of the C3-C4 Transitional Segment of the Internal Carotid Artery.

BACKGROUND: Although the term paraclival carotid pervades recent skull base literature, no clear consensus exists regarding boundaries or anatomical segments. OBJECTIVE: To reconcile various internal carotid artery (ICA) nomenclatures for transcranial and endoscopic-endonasal perspectives, we reexamined the transition between lacerum (C3) and cavernous (C4) segments using a C1-C7 segments schema. In this cadaveric study, we obtained a 360°-circumferential view integrating histological, microsurgical, endoscopic, and neuroradiological analyses of this C3-C4 region and identified a distinct transitional segment. METHODS: In 13 adult, silicone-injected, formalin-fixed cadaveric heads (26 sides), transcranial-extradural-subtemporal and endoscopic-endonasal CT-guided dissections were performed. A quadrilateral area was noted medial to Meckel's cave between cranial nerve VI, anterolateral and posterolateral borders of the lateral-paratrigeminal aspect of the precavernous ICA, and posterior longitudinal ligament. Endoscopically, a medial-paraclival aspect was defined. Anatomical correlations were made with histological and neuroradiological slides. RESULTS: We identified a distinct precavernous C3-C4 transitional segment. In 18 (69%) specimens, venous channels were absent at the quadrilateral area, on the paratrigeminal border of the precavernous ICA. A trigeminal membrane, seen consistently on the superior border of V2, defined the lateral aspect of the cavernous sinus floor. The medial aspect of the precavernous ICA corresponded with the paraclival ICA. CONCLUSION: Our study revealing the juncture of 2 complementary borders of the ICA, endoscopic endonasal (paraclival) and transcranial (paratrigeminal), reconciles various nomenclature. A precavernous segment may clarify controversies about the paraclival ICA and support the concept of a "safe door" for lesions involving Meckel's cave, cavernous sinus, and petrous apex.

Refining Operative Strategies for Optic Nerve Decompression: A Morphometric Analysis of Transcranial and Endoscopic Endonasal Techniques Using Clinical Parameters.

BACKGROUND: Various approaches can be considered for decompression of the intracanalicular optic nerve. Although clinical experience has been reported, no quantitative study has yet compared the extent of decompression achieved by an endoscopic endonasal versus transcranial approach. OBJECTIVE: Toward this aim, our morphometric analysis compared both approaches by quantifying the circumferential degree of optic canal decompression that is possible before any meningeal violation, which would result in cerebrospinal fluid (CSF) leak. METHODS: From 10 cadaver heads, 20 optic canals were sequentially decompressed using an endoscopic endonasal approach and pterional craniotomy with extradural clinoidectomy. Dissections ended before violation of the sphenoid sinus during the transcranial approach, and before intracranial transgression from the endonasal corridor. Based on our study criteria, decompressions were not maximal for either approach, but were maximal before violating the other compartment. Decompression achieved from each approach was quantified using CT scans for each stage. RESULTS: Greater circumferential bony optic canal decompression was obtained from transcranial (245.2°) than endonasal (114.8°) routes (P < .001). By endonasal perspective, the anatomical point where the optic nerve traverses intracranially was approximated by the medial border of the anterior ascending cavernous internal carotid artery. CONCLUSION: Our morphometric analysis comparing optic canal decompression for endonasal and transcranial corridors provides important guidance for this location. Ample visualization and wide exposure can be achieved via a transcranial approach with limited risk of CSF leak. A landmark, where the intracanalicular segment ends and optic nerve traverses intracranially, can mark the extent of decompression safely obtained before risking CSF leak.

Endoscopic transorbital superior eyelid approach: anatomical study from a neurosurgical perspective.

OBJECTIVERecent studies have proposed the superior eyelid endoscopic transorbital approach as a new minimally invasive route to access orbital lesions, mostly in otolaryngology and maxillofacial surgeries. The authors undertook this anatomical study in order to contribute a neurosurgical perspective, exploring the anterior and middle cranial fossa areas through this purely endoscopic transorbital trajectory.METHODSAnatomical dissections were performed in 10 human cadaveric heads (20 sides) using 0° and 30° endoscopes. A step-by-step description of the superior eyelid transorbital endoscopic route and surgically oriented classification are provided.RESULTSThe authors' cadaveric prosection of this approach defined 3 modular routes that could be combined. Two corridors using bone removal lateral to the superior and inferior orbital fissures exposed the middle and anterior cranial fossa (lateral orbital corridors to the anterior and middle cranial base) to unveil the temporal pole region, lateral wall of the cavernous sinus, middle cranial fossa floor, and frontobasal area (i.e., orbital and recti gyri of the frontal lobe). Combined, these 2 corridors exposed the lateral aspect of the lesser sphenoid wing with the Sylvian region (combined lateral orbital corridor to the anterior and middle cranial fossa, with lesser sphenoid wing removal). The medial corridor, with extension of bone removal medially to the superior and inferior orbital fissure, afforded exposure of the opticocarotid area (medial orbital corridor to the opticocarotid area).CONCLUSIONSAlong with its minimally invasive nature, the superior eyelid transorbital approach allows good visualization and manipulation of anatomical structures mainly located in the anterior and middle cranial fossae (i.e., lateral to the superior and inferior orbital fissures). The visualization and management of the opticocarotid region medial to the superior orbital fissure are more complex. Further studies are needed to prove clinical applications of this relatively novel surgical pathway.

The Interlenticulostriate Approach to Very High-Riding Distal Basilar Trunk Aneurysms.

BACKGROUND: Most high-riding distal basilar trunk aneurysms can be surgically approached via the transsylvian route and its orbitozygomatic variant. However, on rare occasions, the basilar bifurcation may be unusually high and an approach above the carotid terminus may be required. OBJECTIVE: In this cadaveric study, we sought to determine the feasibility and exposure limits of the interlenticulostriate approach (ILSA). METHODS: A standard transsylvian approach was performed in 10 cerebral hemispheres of 5 formalin-fixed, silicone-injected cadaver heads. The interpeduncular cistern was exposed via the opticocarotid window, carotid-oculomotor window, and supracarotid ILSA window. The latter was measured and an aneurysm clip or ventriculostomy stylet was placed as high as possible through each corridor. Using noncontrast 3-D rotational angiography, clip/stylet positions were measured relative to the dorsum sellae. RESULTS: ILSA provided a 9.4 × 4.6 mm mean surgical corridor, just enough room for a standard clip applier. This space was limited by the carotid bifurcation inferiorly, the lenticulostriate arteries medially and laterally, and the optic tract superiorly. There was no difference between opticocarotid and carotid-oculomotor windows, in terms of clip position (+8.9 vs +8.6 mm, respectively; P = .78). In contrast, ILSA provided significantly improved superior exposure, compared with either approaches (mean stylet position: +14.3 mm; P = .005). The exposure benefit afforded by ILSA was consistent across all 10 hemispheres, ranging from +2.5 to +8 mm. CONCLUSION: For high-riding distal basilar trunk aneurysms that cannot be reached via the frontotemporal orbitozygomatic approach, ILSA can provide a viable route of access. Vascular neurosurgeons should be familiarized with this approach.

Surgical Freedom Evaluation During Optic Nerve Decompression: Laboratory Investigation.

BACKGROUND AND OBJECTIVE: Various surgical routes have been used to decompress the intracanalicular optic nerve. Historically, a transcranial corridor was used, but more recently, ventral approaches (endonasal and/or transorbital) have been proposed, individually or in combination. The present study aims to detail and quantify the amount of bony optic canal removal that may be achieved via transcranial, transorbital, and endonasal pathways. In addition, the surgical freedom of each approach was analyzed. METHODS: In 10 cadaveric specimens (20 canals), optic canals were decompressed via pterional, endoscopic endonasal, and endoscopic superior eyelid transorbital corridors. The surgical freedom and circumferential optic canal decompression afforded by each approach was quantitatively analyzed. Statistical comparison was carried using a nonpaired Student t test. RESULTS: An open pterional transcranial approach allowed the greatest area of surgical freedom (transcranial, 109.4 ± 33.6 cm2; transorbital, 37.2 ± 4.9 cm2; endonasal homolateral, 10.9 ± 5.2 cm2; and endonasal contralateral, 11.1 ± 5.6 cm2) with widest optic canal decompression compared with the other 2 ventral routes (transcranial, 245.2; transorbital, 177.9; endonasal, 144.6). These differences reached, in many cases, statistical significance for the transcranial approach. CONCLUSIONS: This anatomic contribution provides a comprehensive evaluation of surgical access to the optic canal via 3 distinct, but complementary, approaches: transcranial, transorbital, and endonasal. Our results show that, as expected, a transcranial approach achieved the widest degree of circumferential optic canal decompression and the greatest surgical freedom for manipulation of surgical instruments. Further surgical experience is necessary to determine the proper surgical indication for the transorbital approach to this disease.

The Medial Extra-Sellar Corridor to the Cavernous Sinus: Anatomic Description and Clinical Correlation.

OBJECTIVE: The zenith of surgical interest in the cavernous sinus peaked in the 1980s, as evidenced by reports of 10 surgical triangles that could access the contents of the lateral sellar compartment (LSC). However, these transcranial approaches later became marginalized, first by radiosurgery's popularity and lower morbidity, and then by clinical potential of endoscopic corridors noted in several qualitative studies. Our anatomic study, taking a contemporary look at the medial extra-sellar corridor, gives a detailed qualitative-quantitative analysis for its use with increasingly popular endoscopic endonasal approaches to the cavernous sinus. METHODS: In 20 cadaveric specimens, we re-examined the anatomic landmarks of the medial corridor into the LSC with qualitative descriptions and measurements. An illustrative case highlights a recurrent symptomatic pituitary adenoma that invaded the cavernous sinus approached through the medial corridor. RESULTS: The corridor's shape varied from tetrahedron to hexahedron. Comparing right and left sides, width averaged 3.6 ± 4.5 mm and 4.0 ± 4.4 mm, and height averaged 2.3 mm and 2.1 mm, respectively. About 35% of sides showed ample space for access into the cavernous sinus. Our case report of successful outcome lends support for the safety and efficacy of this endoscopic approach. CONCLUSIONS: Our re-examination of this particular surgical access into the LSC refines the understanding of the medial extra-sellar corridor as a main endoscopic access route to this compartment. Achieving safe access to the contents of the LSC, this 11th triangle is clinically relevant and potentially superior for select lesions in this region.

Drilling of the marginal tubercle to enhance exposure via mini pterional approach: An anatomical study and clinical series of 25 sphenoid wing meningiomas.

BACKGROUND: The marginal tubercle (MT) of zygomatic bone can be an obstacle in the standard mini pterional (MPT) craniotomy; we aim to evaluate the effect of drilling this MT in enhancing the exposure of MPT craniotomy for resection of sphenoid wing meningiomas (SWMs). METHODS: The authors utilized 60 dry skulls to perform the anatomical part of the study. The MT size was reflected by the AB distance, wherein point A is the most prominent part of MT and point B is located on the orbital rim in the same axial plane as point A. The authors analyzed the effect of MT size in masking the sphenozygomatic suture (SZS), which is the most anterior part of the MPT craniotomy. One silicon-injected embalmed specimen was used to demonstrate other modifications to the standard MPT approach. The results of the anatomical analysis were translated into the second part of the study, which consisted of the resection of 25 SWMs. RESULTS: The MT obscured visualization when the AB distance measured 13 mm or greater. In the clinical series of SWMs, drilling such prominent MT maximized exposure during MPT approach. CONCLUSION: The MPT approach could be used for the resection of SWMs. Drilling of prominent MTs can enhance and optimize exposure to SWMs through standard MPT approaches.

Medial and Superior Orbital Decompression: Improving Access for Endonasal Endoscopic Frontal Sinus Surgery.

OBJECTIVE: Visualization by Draf I-III endoscopic access to the frontal sinus via drainage pathways is sometimes inadequate. We compare lateral frontal sinus exposures by Draf approaches versus our modification of removing the medial-superior wall of the orbit while preserving the periorbita. METHODS: Twenty cadaveric heads dissected using Draf IIB, III, and modified Draf III with medial and superior orbital decompression (MSOD) underwent thin-cut computed tomography (CT) scanning. Under image guidance, measurements extended from the midline crista gali to the most lateral point of the frontal sinus. A case report shows the modified Draf III improved frontal sinus access. RESULTS: Comparing Draf IIB and III with Draf III with MSOD, respectively, distances between midline and most lateral point averaged 19.1 mm, 23.7 mm, and 30.4 mm (left) and 18.7 mm, 25.1 mm, and 32.2 mm (right). Differences between Draf III with/without MSOD were 6.65 mm (left) and 7.09 mm (right); 12 heads were excluded because of under-pneumatization of the sinuses. CONCLUSIONS: Draf III with MSOD extended surgical access to lateral regions of the frontal sinus. This extension achieved better visualization and instrumentation with minimal removal of the frontal bone's orbital segment anterior and superior to the anterior ethmoidal artery while preserving the periorbita.

The extended transorbital craniotomy: an anatomic study.

BACKGROUND: Supra-/transorbital approaches are mostly limited to suprasellar and anterior fossa pathologies, whereas lateral supraorbital approaches provide less retrosellar exposure and less overall operative volume, especially in the temporal region. OBJECTIVE: Our cadaveric study proposes removal of the lesser and greater wings of the sphenoid bone to increase both the lateral angle typically achieved with pterional approaches and exposure to the temporal lobe and perisellar region. METHODS: In 5 cadaveric specimens, our 3 steps to expand transorbital exposures included the following: step 1, standard transorbital craniotomy via a 3-cm supra-eyebrow incision; step 2, removal of the lesser sphenoid wing completed extradurally; and step 3, partial removal of the greater sphenoid wing. Operative extension in sylvian, parasellar, and anterolateral temporal exposures were quantified for each step (t test). RESULTS: Step 2 provided the greatest increased exposure in the sylvian and parasellar regions compared with step 3, whereas step 3 provided a significant proportion of the exposure in the lateral temporal region. Finally, the lateral view progressively increased with each subsequent step. CONCLUSION: Our 3-step removal of the lesser and greater wings of the sphenoid bone quantified increased sylvian, anterior temporal, and parasellar exposures for this minimally invasive approach with excellent cosmesis. Its increases the anterolateral view (similar to a subfrontal pterional approach) and offers potential applications to vascular and neoplastic (ie, sphenoid meningiomas) pathologies classically treated via a pterional or frontotemporal orbitozygomatic approach.

Comparing operative exposures of the le fort I osteotomy and the expanded endoscopic endonasal approach to the clivus.

Objectives We compare surgical exposures to the clivus by Le Fort I osteotomy (LFO) and the expanded endoscopic endonasal approach (EEEA). Methods Ten cadaveric specimens were imaged with 1.25-mm computed tomography. After stereotactic navigation, EEEA was performed followed by LFO. Clival measurements included lateral and vertical limits to the midline lower extent of exposure (t test). Results For EEFA and LFO, respectively, maximal lateral exposure in millimeters (mean ± standard deviation) was 24.5 ± 3.7 and 24.5 ± - 3.8 (p = 0.99) at the opticocarotid recess (OCR) and 25.1 ± - 4.1 and 24.1 ± - 3.0 (p = 0.53) at the foramen lacerum level; lateral reach at the hypoglossal canals was 39.0 ± - 5.88 and 56.1 ± - 5.3 (p = 0.0004); and vertical extension was 56.0 ± - 4.1 and 56.3 ± - 3.4 (p = 0.78). Conclusions For clival exposures, LFO and EEEA were similar craniocaudally and laterally at the levels of the OCR and foramen lacerum. LFO achieved greater exposure at the level of the hypoglossal canal.

Vestibular schwannoma or tanycytic ependymoma: Immunohistologic staining reveals.

BACKGROUND: The cerebellopontine angle (CPA) is a common location for primary tumors, most often vestibular schwannomas, and also meningiomas, dermoids, and a host of other neoplasms. Our case report illustrates how radiologic and histopathologic presentations of an unusual variant of ependymal neoplasm can be diagnostically challenging and how accurate diagnosis can affect treatment protocols. CASE HISTORY: Our patient had a CPA mass that was a variant of ependymoma known as tanycytic ependymoma that mimicked vestibular schwannoma radiologically and during intraoperative pathologic examination. Diagnosis as a World Health Organization (WHO) grade II tanycytic ependymoma was supported by its appearance on evaluation of the permanent sections, its diffuse immunoreactivity for glial fibrillary acidic protein (GFAP), and the perinuclear dot-and-ring-like staining for epithelial membrane antigen (EMA). CONCLUSIONS: Our patient's CPA mass initially believed to be a vestibular schwannoma on preoperative evaluation, surgical appearance, and intraoperative pathologic consultation was then correctly diagnosed as a WHO grade II tanycytic ependymoma on permanent histologic sections with the assistance of immunohistochemical stains, including EMA. After this definitive diagnosis, our patient's adjuvant treatment was adjusted. Earlier diagnosis could have provided guidance for goals of resection and prompt initiation of adjuvant treatment.

Segments of the internal carotid artery during endoscopic transnasal and open cranial approaches: can a uniform nomenclature apply to both?

BACKGROUND: The classic anatomic view of the course of the internal carotid artery (ICA) and its segments familiar to neurosurgeons by a 3-dimensional microscopic cranial view may be challenging to understand when seen in the unique 2-dimensional view of transnasal endoscopic surgery. OBJECTIVE: We re-examined our 1996 classification of 7 (C1-C7) segments of the ICA, comparing the arterial course in cadaveric dissections for both a transnasal endoscopic transpenoidal approach and frontotemporal craniotomy. METHODS: Five formalin-fixed cadaveric heads injected with colored silicone underwent thin-cut computed tomographic scanning for bony and vascular analysis. The ICA's intracranial course viewed by transnasal endoscopic dissection was compared with the view of a bilateral frontotemporal crantiotomy, from the petrous (C2) to communicating (C7) segments. RESULTS: Refinement of our 1996 ICA classification provides an anatomical understanding for endoscopic exposures transnasally along an inferior skull base trajectory. The changing course of the ICA, initially termed loop is now termed bend (i.e., implying a change in direction). Four bends are described as the ICA enters into the skull base as C2, C3-C4, C4, and C4-C5. We discuss delineation of certain problematic ICA segments and identify landmarks for endoscopic endonasal approaches. CONCLUSIONS: Our classification of the segments of the ICA achieves consistency without sacrificing either clinical or anatomic accuracy for either transcranial or endoscopic approaches. Universal application of this established nomenclature can avoid new and misleading terms, respects anatomical landmarks delineating segments, and provides a universal language for clear communication between disciplines.

Endoscopic, endonasal variability in the anatomy of the internal carotid artery.

BACKGROUND: Classic three-dimensional schemas of the internal carotid artery (ICA) for transcranial approaches do not necessarily apply to two-dimensional endoscopic views. Modifying an existing ICA segment classification, we define endoscopic orientation for the lacerum (C3) to clinoid (C5) segments through an endonasal approach. METHODS: In 20 cadaveric heads, we classified endoscopic appearance based on shape and angulation of C3 to C5 segments. Distances were measured between both arteries, and between the ICA and pituitary gland. RESULTS: We identified 4 common ICA patterns: types I through III matched side-to-side, whereas type IV was asymmetric. In 80% of specimens, the pituitary gland had direct contact with the ICA. In 20% of specimens, a space existed between the pituitary gland and the cavernous segment. Access to the posterior aspect of the cavernous sinus medial to the cavernous segment was possible without retraction of the artery or pituitary gland. Spaces between the lacerum and cavernous segments were trapezoid (80%) and hourglass (20%). CONCLUSIONS: Distinguishing which ICA type courses between the lacerum and clinoid segments can help clarify the relationships between the artery and its surrounding structures during endoscopic approaches. Adapting the classic terminology of ICA segments provided consistency of endoscopic relevance, defined potential endoscopic corridors, and highlighted the critical step of arterial contact.

Refining the Indications for the Addition of Orbital Osteotomy during Anterior Cranial Base Approaches: Morphometric and Radiologic Study of the Anterior Cranial Base Osteology.

Objectives In anatomic and radiologic morphometric studies, we examine a predictive method, based on preoperative imaging of the anterior cranial base, to define when addition of orbital osteotomy is warranted. Design Anatomic and radiographic study. Setting In 100 dry skulls, measurements in the anterior cranial fossa included three lines and two angles based on computerized tomography (CT) scans taken in situ and validated using frameless stereotactic navigation. The medial angle (coronal plane) was the intersection between the highest point of both orbits and the midpoint between the two frontoethmoidal sutures to each orbital roof high point. The oblique angle (sagittal plane) was the intersection at the midpoint of the limbus sphenoidale. Results No identifiable morphometric patterns were found for our classification of anterior fossae; the two-tailed distribution pattern was similar for all skulls, disproving the hypothetical correlation between visual appearance and morphometry. Orbital heights (range: 6.6-18.7 mm) showed a linear relationship with medial and oblique angles, and they had a linear distribution relative to angular increments. Orbital heights > 11 mm were associated with angles ≥ 20 degrees and more likely to benefit from orbitotomy. Conclusion Preoperative CT measurement of orbital height appears feasible for predicting when orbitotomy is needed, and it warrants further testing.

Cirugía endoscópica endonasal extendida a la región Petro-Clival / Ápex Petroso. Reporte de un caso y revisión de la literatura / Endonasal endoscopic surgery extended to the Petro-Clival / Petrópe region. Case report and literature review

INTRODUCCIÓN: las indicaciones de la cirugía endoscópica endonasal en el tratamiento de tumores de base de cráneo continúan expandiéndose, sobre todo para los tumores extradurales, como son los cordomas. A partir de un caso, nuestro objetivo fue revisar la literatura relevante de estos desafiantes tumores operados bajo esta técnica. CASO CLÍNICO: paciente de 59 de edad con antecedentes de depresión mayor, que comenzó con un cuadro de diplopía por compromiso del VI par izquierdo. Los estudios (CT y RM) mostraron un proceso expansivo en la región del ápex petroso. Se realizó un abordaje endoscópico extendido a la región petro-clival con resección tumoral subtotal. Buena evolución postquirúrgica con desaparición de su diplopía. El diagnóstico histológico fue de Cordoma Condroide. Se indicó radioterapia adyuvante. DISCUSIÓN: a partir del conocimiento y la experiencia en el manejo endoscópico de la patología intraselar se desarrollaron abordajes para el tratamiento de patologías que comprometen la fosa anterior, media e inclusive la fosa posterior. Actualmente, los abordajes endoscópicos, se han extendido a otras áreas de la base de cráneo que de otro modo presentan un reto técnico para la exposición a través de los abordajes transcraneales habituales. El abordaje endoscópico endonasal ofrece una ruta quirúrgica adecuada para la resección del tumor que se presenta en este caso. Las vías que pueden ser utilizados para llegar a la región petroclival a través de la acceso endonasal incluyen la medial (con o sin la movilización de ACI) y la infrapetrosa transterigoidea. En este reporte de caso se analizan las indicaciones del abordaje endoscópico endonasal basado en una revisión de la literatura. CONCLUSIÓN: el abordaje endoscópico endonasal extendido se presenta como una alternativa segura para el tratamiento de determinadas lesiones petro-clivales. Se requieren más estudios anatómicos y clínicos para establecer mejor el rol de este tipo de técnicas en el manejo de las lesiones localizadas en esta región

INTRODUCTION: indications for endoscopic endonasal surgery for the treatment of skull base tumors continue to expand, particularly for extradural tumors, such as chordomas. Based on this case report presentation, we aim to review the literature on the endoscopic technique relevant to the management of these challenging tumors. CASE REPORT: a 59 year-old woman who presented with diplopia due to left sixth nerve palsy underwent imaging studies (CT, MRI) that revealed a mainly intra-osseous expansive process of the left petrous apex. An expanded endoscopic endonasal approach to the petroclival region was performed and the tumor was subtotally resected. The patient recovered from surgery with resolved diplopia. Histopathology was compatible with chondroid chordoma. The radiation therapy was indicated after surgery. DISCUSSION: built upon the bulk experience on the treatment of intrasellar pathology, endonasal endoscopic approaches have been developed for the treatment of skull base lesions involving the anterior, middle and even posterior cranial fossae. Nowadays, the use of these techniques has spread to other areas of the skull base, which otherwise present as a formidable technical challenge for exposure through transcranial approaches. The endonasal endoscopic approach provides an adequate surgical corridor for the resection of the tumor presented in this case report. The alternative corridors that can be utilized to reach the petroclival region through the endonasal endoscopic route include the medial corridor (with or without ICA mobilization) and the transpterygoid infrapetrous corridor. In this article, we discuss the indications for the endoscopic endonasal approach for the case presented, and discuss our choice of approach based on our review of the literature. CONCLUSION: the extended endoscopic endonasal approach presents as a safe alternative for the treatment of select petroclival lesions. Further anatomical and clinical studies are required to better establish the role of the endoscopic endonasal approach for lesions located in this region