Use of time attenuation curves to determine steady-state characteristics before C-arm CT measurement of cerebral blood volume.

INTRODUCTION: Cerebral blood volume (CBV) measurement by flat panel detector CT (FPCT) in the angiography suite seems to be a promising tool for patient management during endovascular therapies. A steady state of contrast agent distribution is mandatory during acquisition for accurate FPCT CBV assessment. To the best of our knowledge, this was the first time that steady-state parameters were studied in clinical practice. METHODS: Before the CBV study, test injections were performed and analyzed to determine a customized acquisition delay from injection for each patient. Injection protocol consisted in the administration of 72 mL of contrast agent material at the injection rate of 4.0 mL/s followed by a saline flush bolus at the same injection rate. Peripheral or central venous accesses were used depending on their availability. Twenty-four patients were treated for different types of neurovascular diseases. Maximal attenuation, steady-state length, and steady-state delay from injection were derived from the test injections' time attenuation curves. RESULTS: With a 15 % threshold from maximum attenuation values, average steady-state duration was less than 10 s. Maximum average steady-state duration with minimal delay variation was obtained with central injection protocols. CONCLUSION: With clinically acceptable contrast agent volumes, steady state is a brief condition; thus, fast rotation speed acquisitions are needed. The use of central injections decreases the variability of steady-state's delay from injection. Further studies are needed to optimize and standardize injection protocols to allow a larger diffusion of the FPCT CBV measurement during endovascular treatments.

Transvenous balloon-assisted transarterial Onyx embolization of transverse-sigmoid dural arteriovenous malformation.

INTRODUCTION: Endovascular treatment of dural arteriovenous malformation is challenging especially if the related dural venous sinus is patent and might be usable for normal venous drainage. METHODS: A new particular venous balloon remodeling technique was described in the treatment of transverse-sigmoid dural arteriovenous malformation by using transarterial Onyx. The goal was obliteration of the malformation with preservation of the dural sinus. Two illustrative cases with 6-month follow-up result were narrated. RESULTS: The penetration of Onyx in the dural arterial feeders was well achieved. Obliteration of the malformation with preservation of the dural sinus was finally demonstrated. CONCLUSION: Transvenous balloon assistance is a useful and feasible technique in the treatment of dural arteriovenous malformation when sinus preservation is in concern.

The outcome of surgical treatment for tumors of the craniocervical junction.

OBJECTIVE: The authors report the clinical, radiological, and surgicalfindings ofpatients with craniocervical junction tumors surgically treated in the institution over the last 8 years. MATERIAL AND METHOD: A retrospective study was performed. Clinical, radiological, and operative data were evaluated, and follow-up information was obtained from outpatient examinations, and telephone interviews. RESULTS: There were 25 patients consisting of nine chordomas, eight meningiomas, three cysts, two schwannomas, one each of aneurysmal bone cyst, plasmacytoma, and metastasis. Twenty-nine operative procedures were performed, classified as 12 anterior nine posterior-lateral, and eight posterior approaches. Gross total removal was achieved in 17 cases, subtotal removal in six cases, and partial removal in two cases. Re-operation was performed in six cases. Median follow-up time was 31 months. The authors found significant improvement in Karnofsky Performance Scale scores. CONCLUSION: Appropriate surgical approaches provide successful tumor removal with less surgical morbidities, nevertheless recurrent tumors occasionally occur and so, long-term follow-up is mandatory.

Patency of the anterior choroidal artery covered with a flow-diverter stent.

OBJECT: The concept of the flow-diverter stent (FDS) is to induce aneurysmal thrombosis while preserving the patency of the parent vessel and any covered branches. In some circumstances, it is impossible to avoid dangerously covering small branches, such as the anterior choroidal artery (AChA), with the stent. In this paper, the authors describe the clinical and angiographic effects of covering the AChA with an FDS. METHODS: Between April 2011 and July 2013, 92 patients with intracranial aneurysms were treated with the use of FDSs in the authors' institution. For 20 consecutive patients (21.7%) retrospectively included in this study, this involved the unavoidable covering of the AChA with a single FDS during endovascular therapy. AChAs feeding the choroid plexus were classified as the long-course group (14 cases), and those not feeding the choroid plexus were classified as the short-course group (6 cases). Clinical symptoms and the angiographic aspect of the AChA were evaluated immediately after stent delivery and during follow-up. Neurological examinations were performed to rule out hemiparesis, hemihypesthesia, hemianopsia, and other cortical signs. RESULTS: FDS placement had no immediate effect on AChA blood flow. Data were obtained from 1-month clinical follow-up in all patients and from midterm angiographic follow-up in 17 patients (85.0%), with a mean length of 9.8 ± 5.4 months. No patient in either group complained of transient or permanent symptoms related to an AChA occlusion. In all cases, the AChA remained patent without any flow changes. CONCLUSIONS: The results of this study suggest that when impossible to avoid, the AChA may be safely covered with a single FDS during intracranial aneurysm treatment, irrespective of anatomy and anastomoses.

Accessing the basilar artery apex: is the temporopolar transcavernous route an anatomically advantageous alternative?

The restricted operative field, difficulty of obtaining proximal vascular control, and close relationship to important anatomic structures limit approaches to basilar apex aneurysms. We used a cadaveric model to compare three surgical transcavernous routes to the basilar apex in the neutral configuration. Five cadaveric heads were dissected and analyzed. Working areas and length of exposure provided by the transcavernous (TC) approach via pterional, orbitozygomatic, and temporopolar (TP) routes were measured along with assessment of anatomic variation for the basilar apex region. In the pterional TC and orbitozygomatic TC approaches, the mean length of exposure of the basilar artery measured 6.9 and 7.2 mm, respectively (p = NS). The mean length of exposure in a TP TC approach increased to 9.3 mm (p < 0.05). Compared with the pterional and orbitozygomatic approaches, the TP TC approach provided a larger peribasilar area of exposure ipsilaterally and contralaterally (p < 0.05). The multiplanar working area related to the TP TC approach was 77.7 and 69.5% wider than for the pterional TC and orbitozygomatic TC, respectively. For a basilar apex in the neutral position, the TP TC approach may be advantageous, providing a wider working area for the basilar apex region, improving maneuverability for clip application, fine visualization of perforators, and better proximal control.

Accessing the recesses of the fourth ventricle: comparison of tonsillar retraction and resection in the telovelar approach.

OBJECTIVE: To compare the effectiveness of the telovelar approach with tonsillar manipulation for approaching the recesses of the fourth ventricle. METHODS: A telovelar approach was performed in 8 injected cadaveric heads. Areas of exposure were measured for the superolateral and lateral recesses. Horizontal angles were evaluated by targeting the cerebral aqueduct and medial margin of the lateral recess. Quantitative comparisons were made between the telovelar dissections and various tonsillar manipulations. RESULTS: Tonsillar retraction provided a comparable exposure of the superolateral recess with tonsillar resection (26.4 +/- 17.6 vs 25.2 +/- 12.5 mm2, respectively; P = .825). Tonsillar resection significantly increased exposure of the lateral recess compared with tonsillar retraction (31.1 +/- 13.3 vs 20.2 +/- 11.5 mm2, respectively; P = .002). Compared with tonsillar retraction, the horizontal angle to the lateral recess increased after either contralateral tonsillar retraction (22.7 +/- 4.8 vs 36.7 +/- 6.5 degrees) or tonsillar resection (22.7 +/- 4.8 vs 31.5 +/- 7.6 degrees; all adjusted P < .01). The horizontal angle to the cerebral aqueduct increased significantly with tonsillar resection compared with tonsillar retraction (17.6 +/- 2.3 vs 13.2 +/- 2.8 degrees; P < .001) CONCLUSION: Compared with tonsillar retraction, tonsillar resection provides a wider corridor to, and a larger area of exposure of, the cerebral aqueduct and lateral recess. Contralateral tonsillar retraction improves access to the lateral recess by widening the surgical view from the contralateral side.

The challenge of access to the pontomesencephalic junction: an anatomical study of lateral approach and exposure.

We quantitatively compared relative merits of lateral approaches to the pontomesencephalic junction (PMJ): anterior petrosectomy, subtemporal transtentorial, posterior petrosectomy, and retrosigmoid transtentorial. In dissected cadaveric heads, lengths of exposure were measured anteriorly from CN V along the pontomesencephalic sulcus (PMS); posterosuperiorly along the lateral mesencephalic sulcus (LMS); and posteroinferiorly along the interpeduncular sulcus (IPS). Subtemporal transtentorial approach provided best anterior exposure along the PMS (23.8 ± 4.5 mm). Posterosuperior exposures were comparable for all approaches except anterior petrosectomy (limited). Posteroinferior exposure was most with subtemporal transtentorial approach (13.2 ± 2.8 mm). CN V entry/exit point was identified through all approaches, except for subtemporal transtentorial; shortest surgical depth with posterior petrosectomy was 43.7 ± 5.5 mm. PMS-LMS-IPS convergence point: reached through all approaches, except for anterior petrosectomy (limited); shortest surgical depth with posterior petrosectomy was 40.3 ± 4.3 mm. Anterior petrosectomy provides direct anterolateral views of the pons not afforded by subtemporal approach. Subtemporal transtentorial approach provides optimal posterolateral view to the PMJ and cerebellar peduncles. Retrosigmoid transtentorial approach offers wide exposure of the lateral surface, limited on the posteroinferior PMJ by the cerebellum. The small opening of posterior petrosectomy creates an awkward corridor to anterior PMJ targets but provides a direct and shortest route to the cerebellar peduncles.

Anatomical relationships of intracavernous internal carotid artery to intracavernous neural structures.

The objective is to correlate the intracavernous internal carotid artery (ICA) with the position of the intracavernous neural structures. The cavernous sinuses of nine injected cadaveric heads were dissected bilaterally. As measured on computed tomographic angiograms from 100 adults, anatomical relationships and measurements of intracavernous ICA and neural structures were studied and correlated to the intracavernous ICA curvature. Intracavernous ICAs were classified as normal and redundant. The meningohypophyseal trunk (MHT) of normal ICAs appeared to be closely related to the abducens nerve compared with redundant ICAs (5.5 ± 2.1 mm versus 10.0 ± 2.5 mm, respectively; p = 0.001). The position of the inferolateral trunk (ILT) varied along the horizontal segment of the intracavernous ICA. On imaging studies the ICA curvature correlated with the kyphotic degree of the skull and similarity of the ICA curvature between sides. The safety margin for preventing iatrogenic intracavernous nerve injury during surgical exploration or transarterial embolization of vascular lesions around the MHT is high with redundant ICAs. In contrast, a transvenous endovascular approach via the inferior petrosal sinus may be too distant to reach the MHT when ICAs are redundant. Approaching lesions of the inferolateral trunk may be the same regardless of ICA type.

Quantitative analysis of variants of the far-lateral approach: condylar fossa and transcondylar exposures.

BACKGROUND: The rationale for choosing between the condylar fossa and transcondylar variations of the far-lateral approach requires understanding of the relationships between the occipital condyle, jugular tubercle, and hypoglossal canal. OBJECTIVE: We examined the anatomic relationship of these 3 structures and analyzed the effect that changes in these relationships have on the surgical exposure and angle of attack for these 2 approaches. METHODS: Anatomic measurements of 5 cadaveric heads from 3-dimensional computed tomographic scans were compared with direct measurements of the same specimens. The condylar fossa and transcondylar approach were performed sequentially in 8 of 10 sides. Surgical exposure and angle of attack were measured after each exposure. RESULTS: The jugular tubercle (JT) angle (JTA) measures the angle formed by reference points on the condyle, hypoglossal canal, and JT. When the JT and occipital condyle are not prominent (JTA > 180 degrees ), the transcondylar approach does not significantly increase petroclival or brainstem exposure compared with the condylar fossa approach; however, it does significantly increase the angle of attack to the junction of the posterior inferior cerebellar and vertebral arteries and the surgical angle for the medial part of the JT (P < .05). CONCLUSION: The condylar fossa and transcondylar approaches provide similar exposures of the petroclivus and brainstem when the JT and occipital condyle are not prominent (JTA > 180 degrees on 3-dimensional computed tomographic). However, for lesions below the hypoglossal canal, the transcondylar approach is preferred because it significantly increases the angle of attack.

Rapid, simple technique to extend depth of field in microneurosurgical images: technical note.

OBJECTIVE: To increase the extent of the depth of field and focal sharpness in highly magnified image series from cadaveric microneurosurgical anatomic study or live surgery photographs obtained with the operating microscope, providing a higher quality and more satisfactory photographic and imaging experience. METHODS: We used a computer workstation, CombineZM software (Alan Hadley, United Kingdom, www.hadleyweb.pwp.blueyonder.co.uk/), an injected cadaver head specimen, and an operating microscope equipped with a digital single-lens reflex camera. Fifteen images were obtained of the dissection area through an anterior petrosal approach. The focus point was fixed to different points in each image. The images were loaded into CombineZM software for processing. RESULTS: The stacking process of photographs with CombineZM freeware provides significant increase in extent of depth of field and wider area of image clarity, producing a sharp, high-quality image. CONCLUSION: An image processed from a stack of photographs from cadaveric microneurosurgical studies or from the operating microscope in live surgery can be rendered to show extended 3-dimensional depth of field and clarity. This method offers improvements for editing, displaying, and publishing neurosurgical anatomic images.

Transfrontoethmoidal approach to medial intraconal lesions.

Object The standard superior craniotomy approach through the orbital roof is obstructed by numerous muscles, nerves, and vessels. Accessing the medial intraconal space also involves considerable brain retraction. The authors present a modified approach through the frontal sinus that overcomes these limitations. Methods Seven fixed silicone-injected cadaveric specimens were dissected bilaterally. In addition to the superior orbital wall, the ethmoidal sinuses and medial orbital wall were removed. The anatomical relationships between the major neurovascular complexes in the medial intraconal space and the optic nerve were observed. Results Intraconally, working space was created both in a "superior window" between the superior oblique and levator palpebrae muscle and in a "medial window" between the superior oblique and medial rectus muscle. The superior window mainly created an ipsilateral trajectory to the deep target. The medial window, which created a contralateral trajectory, provided a more inferior view of the medial intraconal space. Removal of the medial orbital wall further widened the exposure obtained from the superior window. The combination of these working windows makes the medial surface of the optic nerve available for exploration from multiple angles. Most of the major neurovascular complexes of the posterior orbit can be retracted safely without impinging on the optic nerve. Conclusions This novel extradural transfrontoethmoidal approach affords a direct view to the medial posterior orbit without major conflicts with intraconal neurovascular structures and requires minimal brain manipulation. The approach appears to offer advantages for medially located intraconal lesions.

Comparative analysis of posterior approaches to the medial temporal region: supracerebellar transtentorial versus occipital transtentorial.

OBJECTIVE: Cortical and subcortical lesions in the posterior portion of the medial temporal region (MTR) are routinely resected through the supracerebellar transtentorial (SCTT) or occipital transtentorial (OCTT) route. We compared the exposures provided by these 2 approaches to this region. METHODS: Eight sides of injected cadaver heads were dissected using both approaches. Identical deep target points were collected for SCTT and OCTT routes while accepting variations in initial exposures. Data gathered with the P2-P3 junction as an apex created 2 adjoining triangles (anterior and posterior) in the middle and posterior MTR. Real, projected, and freedom areas were calculated for comparison. RESULTS: The approach-related differences for the real and projected areas were expressed in relative values. There were no differences in the percentage of projected area between the 2 approaches (e.g., working in the middle of the opening, anterior triangle: SCTT, 5.2 +/- 4.1%; OCTT, 8.4 +/- 5.6%; P = 0.313; posterior triangle: SCTT, 8.6 +/- 3.8%; OCTT, 8.8 +/- 6.3%; P = 0.937). Freedom areas for the SCTT approach were smaller than those for the OCTT approach at many deep points (P < 0.05), except in the posterior margin of the MTR (P = 0.21). CONCLUSION: The SCTT and OCTT approaches provided no differences in surgical views to the MTR. However, the OCTT approach provides a wider corridor for surgical manipulation compared with the SCTT approach in most parts of the MTR. These data may help neurosurgeons to select a favorable approach to specific lesions of the MTR.

Comparative analysis of extensions of transbasal approaches: effect on access to midline and paramedian structures.

We sought to quantitate the effect of extensions of transbasal approaches (TBAs) on midline and paramedian targets of the cranial base. Eight silicone-injected cadaveric heads were dissected with extensions of TBA level I removal of the orbital bar. Objective measures were the comparisons of the accessibility of midline and paramedian targets with progressive dissections by level II detachment of the medial canthal ligaments and removal of the nasal bone and by level III removal of the lateral orbital walls with lateral orbital retraction. Mean areas of freedom increased for most targets with progressive bone removal. For midline targets, the most effective freedom increment was at the pituitary gland (level II: 28.8%, p = 0.05; level III: 107.1%, p < 0.001). For paramedian targets, the best freedom increment was for the foramen rotundum (level II: 56.4%; level III: 134.5%, all p < 0.001). Extensions of the TBA can increase the surgical corridor to midline and paramedian structures, especially for pituitary and maxillary regions. Level II exposure offers no clear benefit for most targets except the foramen rotundum. With level III exposure, all targets are effectively exposed compared with levels I and II.

Greater superficial petrosal nerve dissection: back to front or front to back?

OBJECTIVE: To introduce a novel surgical technique for the dissection of the greater superficial petrosal nerve (GSPN) in the middle fossa approach. METHODS: Interdural temporal elevation was performed with a front-to-back technique to preserve the GSPN in 12 sides of 6 injected cadaveric heads dissected through a middle fossa approach. RESULTS: The GSPN emerged from the facial hiatus in a shallow bony groove proximally, ran into a deeper sphenopetrosal groove, and eventually reached the mandibular nerve. With front-to-back dissection, this nerve was easily identified at the posterior border of the mandibular nerve. Dissection from front to back minimized the retraction force applied to the proximal part of the GSPN, which was preserved in all specimens. CONCLUSION: The temporal dura can be elevated safely with a front-to-back technique to preserve the GSPN and to help maintain the physiological integrity of the facial nerve.

Comparative analysis of the retrosigmoid and lateral supracerebellar infratentorial approaches along the lateral surface of the pontomesencephalic junction: a different perspective.

OBJECTIVE: To quantitatively assess the working distance and angle of attack among the retrosigmoid (RS), lateral supracerebellar (LS), and extreme lateral supracerebellar (EL) views on the lateral surface of the pontomesencephalic junction. METHODS: Eight sides of silicone-injected fixed cadaveric heads were dissected using the three approaches. All predetermined anatomic points were collected by use of a frameless stereotactic device. The length of exposure and the angle of attack were calculated and compared. Predissection imaging was obtained for illustration. RESULTS: The LS and EL approaches created a horizontal working space as compared with the vertical working space created by the RS approach. The RS view gained less posterior exposure margin than the LS and EL views (posterosuperior margin values: RS, 4.3 +/- 1.7 mm; LS, 6.4 +/- 2.0 mm; EL, 7.3 +/- 2.0 mm; P < 0.001; posteroinferior margin: RS, 2.7 +/- 2.7 mm; LS, 4.9 +/- 2.8 mm; EL, 8.3 +/- 2.5 mm; P < 0.001). When the tentorium is intact, transverse sinus retraction significantly accentuates the field of view by the EL approach compared with the LS approach at both the anteroinferior (P < 0.05) and posteroinferior (P < 0.001) margins. Between the supracerebellar types, the vertical angle of attack was significantly improved and the horizontal angle was significantly decreased when complete venous retraction was performed. CONCLUSION: The supracerebellar views offer greater advantage over the RS view when the surgeon is working more posteriorly on the pontomesencephalic junction. Between the supracerebellar views, venous retraction creates a significantly wider vertical angle and also improves the exposure when the surgeon is working more inferiorly.

Quantitative analysis of exposure of staged orbitozygomatic and retrosigmoid craniotomies for lesions of the clivus with supratentorial extension.

OBJECTIVE: A two-stage approach using orbitozygomatic (OZ) and retrosigmoid (RS) craniotomies is one option for the management of petroclival lesions with supratentorial extension. The goal of this study was to investigate the supratentorial and infratentorial exposures of the clivus obtained through this staged approach. METHODS: Formalin-fixed, silicon-injected specimens underwent stereotactic imaging. Six paired OZ and RS craniotomies were performed. Neuronavigation was used to determine the areas and limits of exposure and to plot these areas on three-dimensional reconstructions of the skull base. RESULTS: The mean area of exposure of the parasellar region and clivus through the OZ craniotomy was 640 +/- 75 mm. Visualization of the parasellar region, cavernous sinus, and upper cranial nerves was achieved. The ventral brainstem corresponding to the cranial quarter of the clivus was visualized. The mean area of exposure of the clivus and petrous bone through the RS was 1930 +/- 250 mm. In the cranial quarter of the clivus, there was a small region of overlap in exposure between the two craniotomies. The limits of exposure are described. CONCLUSION: OZ and RS craniotomies provide complementary exposure with limited redundancy. Significant visualization of the parasellar region, clivus, and surrounding bony landmarks is obtained. The primary limitation is exposure of the contralateral half of Zones II and III of the clivus. This strategy represents a reasonable option for accessing paracentral petroclival lesions with a supratentorial extension.