[Microvascular Decompression for Trigeminal Neuralgia Due to Venous Compression].

In microvascular decompression surgery for trigeminal neuralgia, the veins are essential as an anatomical frame for the microsurgical approach and as an offending vessel to compress the trigeminal nerve. Thorough arachnoid dissection of the superior petrosal vein and its tributaries provides surgical corridors to the trigeminal nerve root and enables the mobilization of the bridging, brainstem, and deep cerebellar veins. It is necessary to protect the trigeminal nerve by coagulating and cutting the offending vein. We reviewed the clinical features of trigeminal neuralgia caused by venous decompression and its outcomes after microvascular decompression. Among patients with trigeminal neuralgia, 4%-14% have sole venous compression. Atypical or type 2 trigeminal neuralgia may occur in 60%-80% of cases of sole venous compression. Three-dimensional MR cisternography and CT venography can help in detecting the offending vein. The transverse pontine vein is the common offending vein. The surgical cure and recurrence rates of trigeminal neuralgia with venous compression are 64%-75% and 23%, respectively. Sole venous compression is a unique form of trigeminal neuralgia. Its clinical characteristics differ from those of trigeminal neuralgia caused by arterial compression. Surgical procedures to resolve venous compression include nuances in safely handling venous structures.

Low back pain improvement after cervical laminoplasty in patients without tandem lumbar stenosis.

PURPOSE: This study aimed to demonstrate the impact of lumbar spinal stenosis (LSS) on LBP after cervical laminoplasty for cervical spinal stenosis by analyzing the clinical characteristics and surgical outcomes. METHODS: This retrospective cohort study analyzed 56 consecutive patients with cervical spinal stenosis who underwent cervical laminoplasty. Data on age, sex, Japanese Orthopaedic Association (JOA) scores, JOA Back Pain Evaluation Questionnaire (BPEQ), and visual analog scale (VAS) were collected. The patients with VAS for LBP ≥ 30 or more were included and divided into two groups: without LSS [LSS (-)]or with LSS [LSS (+)]. Preoperative clinical characteristics and postoperative changes were compared between the groups. RESULTS: Preoperative VAS for LBP were 50.7 ± 16.2 mm and 59.8 ± 19.5 mm in the LSS (+) and LSS (-), respectively (p = 0.09). Patients in the LSS (-) were younger (57.6 ± 11.2 vs. 70.7 ± 8.6, p < 0.001) and showed significantly milder preoperative lumbar symptoms in terms of JOA and BPEQ. Patients in the LSS (-) group showed more postoperative changes in low back pain (18.3 ± 26.4 vs. - 8.3 ± 37.6, p = 0.005) and lumbar function (10.8 ± 25.7 vs. - 2.0 ± 22.5, p = 0.04) at BPEQ, and higher recovery in terms of VAS of LBP (23.0 ± 23.8 mm vs. 5.3 ± 25.9 mm, p = 0.008) and buttocks and low limbs (12.5 ± 35.0 mm vs. - 4.3 ± 24.4 mm, p = 0.029). Nine patients in the LSS (+) group underwent lumbar surgery at 12.8 ± 8.5 months after cervical laminoplasty. CONCLUSION: LBP improved after cervical laminoplasty in patients without lumbar stenosis.

Intramedullary feeder aneurysm of a cervical epidural arteriovenous fistula causing myelopathy: a case report and literature review.

While a craniocervical junction (CCJ) epidural arteriovenous fistula (EDAVF) may present with hemorrhagic myelopathy from an associated feeder aneurysm on rare occasions, non-hemorrhagic myelopathy from such an aneurysm remains unreported. A woman in her late sixties presented with cervical myelopathy due to a non-hemorrhagic intramedullary aneurysm associated with CCJ-EDAVF. The intramedullary aneurysm originated from the spinal pial artery supplied by the anterior spinal artery. Direct surgical fistula coagulation and feeder obliteration resulted in the disappearance of the aneurysm and myelopathy improvement. This report illustrates the first case of a non-hemorrhagic intramedullary aneurysm associated with CCJ-EDAVF successfully treated with direct surgery.

Deep brain stimulation for refractory obsessive-compulsive disorder (OCD): emerging or established therapy?

A consensus has yet to emerge whether deep brain stimulation (DBS) for treatment-refractory obsessive-compulsive disorder (OCD) can be considered an established therapy. In 2014, the World Society for Stereotactic and Functional Neurosurgery (WSSFN) published consensus guidelines stating that a therapy becomes established when "at least two blinded randomized controlled clinical trials from two different groups of researchers are published, both reporting an acceptable risk-benefit ratio, at least comparable with other existing therapies. The clinical trials should be on the same brain area for the same psychiatric indication." The authors have now compiled the available evidence to make a clear statement on whether DBS for OCD is established therapy. Two blinded randomized controlled trials have been published, one with level I evidence (Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score improved 37% during stimulation on), the other with level II evidence (25% improvement). A clinical cohort study (N = 70) showed 40% Y-BOCS score improvement during DBS, and a prospective international multi-center study 42% improvement (N = 30). The WSSFN states that electrical stimulation for otherwise treatment refractory OCD using a multipolar electrode implanted in the ventral anterior capsule region (including bed nucleus of stria terminalis and nucleus accumbens) remains investigational. It represents an emerging, but not yet established therapy. A multidisciplinary team involving psychiatrists and neurosurgeons is a prerequisite for such therapy, and the future of surgical treatment of psychiatric patients remains in the realm of the psychiatrist.

Infratentorial developmental venous anomaly concurrent with a cavernoma and dural arteriovenous fistula.

OBJECTIVES: While developmental venous anomaly (DVA) may be associated with cavernous malformation, mixed vascular malformation associated with dural arteriovenous fistula (dAVF) has not been previously reported. We observed a case with rare association of infratentorial DVA, cavernous malformation, and dAVF that presented with cerebellar ataxia. We report our endovascular treatment for this complex cerebrovascular condition. CASE PRESENTATION: A 32-year-old woman with ataxia had an infratentorial DVA associated with a cavernoma and dAVF. The dAVF had two shunting points. The dAVF was fed by the posterior meningeal arteries and drained through the sigmoid sinus into the transverse sinus. The dAVF was also fed by the occipital artery and retrogradely drained through the left jugular bulb into the dilated collecting vein of the DVA. Endovascular embolization was performed for the dAVF and dilated collecting vein of the DVA. Postoperative complications did not occur after embolization with no recurrence for three years. CONCLUSIONS: This is the first reported case of infratentorial DVA associated with a cavernoma and dAVF. Endovascular treatment was effective in treating this symptomatic complex cerebrovascular disorder.

Carotid Micromesh Stent for the Cervical Carotid Artery Dissecting Aneurysm in a Patient with Vascular Eagle Syndrome.

OBJECTIVES: An elongated styloid process may cause vascular Eagle syndrome that includes cervical carotid artery (CCA) dissection with stenosis and aneurysm formation. There are only four reported cases with vascular Eagle syndrome-related CCA dissecting aneurysm treated with carotid artery stenting (CAS). This is the first report of applying a dual-layer nitinol micromesh stent (CASPER) for vascular Eagle syndrome-related CCA dissecting aneurysm. CASE PRESENTATION: A 38-year-old man presented with a sudden onset of aphasia and right hemiplegia. Cerebral angiography demonstrated the left CCA dissecting aneurysm. The superior trunk of the left middle cerebral artery (MCA) was also occluded, and emergent thrombectomy was performed. Computed tomography with angiography (CTA) revealed that a 33 mm-long styloid process compressed the CCA at the aneurysm formation. Three weeks later, a CASPER stent was applied for the CCA aneurysm under the flow reversal system. Immediately after stent placement, blood flow in the aneurysm became stagnant, and postoperative CTA demonstrated regression of the aneurysm. The aneurysm did not recur for 6 months with no styloid process resection. CONCLUSIONS: The dual-layer nitinol micromesh stent (CASPER) was useful to treat vascular Eagle syndrome-related CCA dissecting aneurysm.

[Posterior Subthalamic Area, Pallidothalamic Tract, and Pedunculopontine Nucleus:Deep Brain Stimulation Targets for Parkinson's Disease and Essential Tremor].

This article reviews the stereotactic targets in the posterior subthalamic area(PSA), fields H1/H2 of Forel(pallidothalamic tract), and the pedunculopontine nucleus(PPN)to complement the preceding articles on stereotactic and functional neurosurgery for movement disorders in the present issue of No Shinkei Geka. Two regions within the subthalamus, the PSA and fields H1/H2 of Forel, are the revisited stereotactic targets to treat movement disorders. Currently, the PSA is often utilized to treat essential tremor and various types of tremor. Fields H1/H2 of Forel are investigated as a target for magnetic resonance-guided focused ultrasound to treat motor symptoms and motor complications in patients with Parkinson's disease. For the past twenty years, the PPN has been investigated to treat refractory gait freezing and fall in patients with Parkinson's disease. These revisited and novel targets may be utilized as substitutes and complements for the present standard stereotactic targets.

[Risk Factors for Early Progression of Carotid Stenosis after Cervical Radiation Therapy].

OBJECTIVE: Carotid stenosis may occur as a late complication following cervical radiation therapy(RT);however, it may also progress in the early post-RT period. This study aimed to characterize the clinical features associated with the early progression of post-RT carotid stenosis. METHODS: We retrospectively reviewed clinical records of 30 patients who had undergone unilateral or bilateral cervical RT between January 2010 and November 2014. We analyzed the pre- and post-RT stenosis of their carotid arteries using contrast-enhanced computed tomography images. The arteries were classified as progressive or non-progressive according to the presence or absence of stenosis progression within five years after RT. Using univariate and multivariate analyses, we evaluated the following potential clinical risk factors:age;gender;history of hypertension, hyperlipidemia, diabetes mellitus, coronary artery disease, or smoking habit;antiplatelet or statin use;radiation dose;and prior presence of carotid stenosis before RT. RESULTS: In total, we reviewed 57 irradiated carotid arteries and identified 9 with early post-RT progression. Carotid stenosis before RT was observed in 88.9% of arteries in the progressive group but only 2% of arteries in the non-progressive group and it predicted progression(univariate and multiple logistic regression analyses, p<0.0001). No other clinical characteristics had a significant association with the progression of carotid stenosis. CONCLUSION: Prior presence of carotid stenosis may be a risk factor for its early progression after RT. Pre-RT screening of cervical arteries may be useful, and strict management of carotid stenosis is critical in patients with cervical radiation therapy.

Extradural Anterior Clinoidectomy and Optic Canal Unroofing for Paraclinoid and Basilar Aneurysms: Usefulness of a No-Drill Instrumental Method.

The authors describe extradural anterior clinoidectomy without the use of a high-speed drill or ultrasonic device to clip paraclinoid and basilar aneurysms, which can eliminate potential complications related to traditional power drilling or ultrasonic device use. This method involves four steps: (1) partial osteotomy of the sphenoid wing at the superior orbital fissure (SOF); (2) peeling of the dura propria of the temporal lobe from the inner cavernous membrane of the SOF; (3) isolation and resection of the exposed meningo-orbital band to expose the superolateral aspect of the anterior clinoid process (ACP); and (4) piecemeal rongeuring of ACP and the roof of the optic canal. The entire procedure was performed using surgical instruments, including micro-rongeurs, a fine Kerrison punch, and micro-dissectors. Subsequently, intradural neck clipping was performed. Twenty consecutive patients with paraclinoid and basilar aneurysms successfully underwent clipping after this non-drill extradural clinoidectomy. Minor morbidity was noted in two patients (cerebrospinal fluid leakage in one and transient oculomotor palsy in the other). The non-drill method is a simple, easy, safe, and quick alternative to traditional power drilling in extradural clinoidectomy, and this method can avoid morbidity related to direct mechanical/thermal injury of important neurovascular structures.

Bridging veins and veins of the brainstem in microvascular decompression surgery for trigeminal neuralgia and hemifacial spasm.

OBJECTIVE In microvascular decompression surgery for trigeminal neuralgia and hemifacial spasm, the bridging veins are dissected to provide the surgical corridors, and the veins of the brainstem may be mobilized in cases of venous compression. Strategy and technique in dissecting these veins may affect the surgical outcome. The authors investigated solutions for minimizing venous complications and reviewed the outcome for venous decompression. METHODS The authors retrospectively reviewed their surgical series of microvascular decompression for trigeminal neuralgia and hemifacial spasm in patients treated between 2005 and 2017. Surgical strategies included preservation of the superior petrosal vein and its tributaries, thorough dissection of the arachnoid sleeve that enveloped these veins, cutting of the inferior petrosal vein over the lower cranial nerves, and mobilization or cutting of the veins of the brainstem that compressed the nerve roots. The authors summarized the patient characteristics, operative findings, and postoperative outcomes according to the vascular compression types as follows: artery alone, artery and vein, and vein alone. They analyzed the data using chi-square and 1-way ANOVA tests. RESULTS The cohort was composed of 121 patients with trigeminal neuralgia and 205 patients with hemifacial spasm. The superior petrosal vein and its tributaries were preserved with no serious complications in all patients with trigeminal neuralgia. Venous compression alone and arterial and venous compressions were observed in 4% and 22%, respectively, of the patients with trigeminal neuralgia, and in 1% and 2%, respectively, of those with hemifacial spasm (p < 0.0001). In patients with trigeminal neuralgia, 35% of those with artery and venous compressions and 80% of those with venous compression alone had atypical neuralgia (p = 0.015). The surgical cure and recurrence rates of trigeminal neuralgias with venous compression were 60% and 20%, respectively, and with arterial and venous compressions the rates were 92% and 12%, respectively (p < 0.0001, p = 0.04). In patients with hemifacial spasm who had arterial and venous compressions, their recurrence rate was 60%, and that was significantly higher compared to other compression types (p = 0.0008). CONCLUSIONS Dissection of the arachnoid sleeve that envelops the superior petrosal vein may help to reduce venous complications in surgery for trigeminal neuralgia. Venous compression may correlate with worse prognosis even with thorough decompression, in both trigeminal neuralgia and hemifacial spasm.

[Therapeutic Effects of Low-Dose Bevacizumab for the Treatment of Recurrent Brain Metastases].

OBJECTIVE: Molecularly targeted therapy has been adopted to treat a number of cancers. Bevacizumab, a recombinant humanized monoclonal antibody against vascular endothelial growth factor, is a representative agent used in molecularly targeted therapeutic regimens. However, the therapeutic effect of bevacizumab for the treatment of brain metastases remains unknown. We report the clinical effects of low dose bevacizumab(≤2.5mg/kg/week)to treat recurrent brain metastases. METHODS: We retrospectively analyzed patients with brain metastases who had been treated with bevacizumab between 2012 and 2016 at our institution. We identified clinical characteristics, including age, gender, primary tumor site, dose of bevacizumab, therapeutic and adverse effects, and magnetic resonance imaging results. The lesions were assessed with the RECIST criteria based on gadolinium-enhanced T1-weighted, T2-weighted, and FLAIR images. Statistical analysis was performed using t-test and Fisher's exact test. RESULTS: The cohort comprised 26 patients(8 men, 18 women)with a median age of 61 years(range 39-82 years). There were no significant clinical differences between the low dose and non-low dose groups. Patients in the low dose group did not report any adverse effects from bevacizumab. Three patients with brain metastases from colon cancer are illustrated to report the clinical course of low dose bevacizumab. CONCLUSION: Low dose bevacizumab may be a safe and effective therapeutic option to treat recurrent brain metastases from bevacizumab-sensitive cancers.

Coaxial interleaved stimulation of the thalamus and subthalamus for treatment of Holmes tremor.

Holmes tremor is often treated with multiple deep brain stimulation (DBS) electrodes. The authors describe a novel technique to suppress the tremors by effectively utilizing a single electrode. A 16-year-old boy presented with severe right arm tremor following a midbrain injury. A DBS electrode was implanted into the ventral oralis nucleus of the thalamus (VO) and the subthalamic region. While individual stimulation of each target was ineffective, an interleaved dual stimulation of both targets has been effective for 6 years. Coaxial interleaved stimulation of the VO and the subthalamic region is useful for treating Holmes tremor. The video can be found here: https://youtu.be/tSwGh3vy68c .

Posterior atlantoaxial fusion as treatment option for extracranial vertebral artery dissecting aneurysm: a case report and literature review.

Symptomatic extracranial vertebral artery (VA) dissection may need surgery. We describe such a case successfully treated with atlantoaxial fusion based on its rare dynamic angiographic findings. A 27-year-old woman suffered from repeated brainstem and cerebellar infarctions from a left extracranial VA dissecting aneurysm. Dynamic angiography showed the dissecting aneurysm of the V3 segment in the neutral head position, and deflation of the aneurysm during rightward head rotation. She underwent posterior atlantoaxial fusion, and the lesion was repaired with no subsequent ischemia. Posterior atlantoaxial fusion can be an option for some extracranial VA dissections with preserving its anterograde blood flow.

[Treatment of Non-Traumatic Spinal Epidural Hematoma:A Report of Five Cases and a Systematic Review of the Literature].

Objective:Non-traumatic spinal epidural hematoma(SEH)is relatively rare. We report five cases of SEH, review the relevant literature, and discuss the current treatment strategies for non-traumatic SEH in Japan. Methods:Clinical data of cases with non-traumatic SEH treated at our institute from 2008 to 2015 were retrospectively analyzed. In addition, we identified the relevant literature using the Japan Medical Abstracts Society databases for peer-reviewed articles published from Jan 1, 1995 to Aug 31, 2015. The search terms "spinal", "epidural hematoma", and "non-traumatic OR spontaneous" were used. Treatment strategies were summarized according to the treatment criteria. Results:Five patients(1 man and 4 women;age, 59-86 years;mean age, 74 years)were treated for SEH. Hematomas were located in the cervical(n=1), cervicothoracic(n=2), thoracic(n=1), and thoracolumbar(n=1)regions. All patients suffered sudden neck and/or back pain followed by subsequent neurological deterioration. Four patients were under antithrombotic treatment, and underwent laminectomy and drainage of the hematoma due to severe and progressive neurological deficits. All patients demonstrated significant neurological recovery. Seventy-seven articles from domestic institutes and hospitals were identified. Their criteria for conservative and surgical treatments differed based on the time from the onset and severity. Conclusion:Five cases of non-traumatic SEH were treated successfully. Patients with moderate to severe neurological deficit need timely surgical management, while non-surgical treatment may be indicated in mild deficits. To standardize the optimal treatment for non-traumatic SEH, an appropriate assessment system incorporating the time from onset and severity of neurological impairment should be established.

[A Single-Stage Combined Supra- and Infra-Sellar Approach for Recurrent Large Pituitary Adenomas:Report of Two Cases].

Despite the recent technological advances in operative instruments and development of novel techniques for endoscopic skull-base surgeries, surgical treatment of primary or recurrent large/giant pituitary adenomas remains a challenge. Postoperative hemorrhage from the residual tumor and the associated impairment of the adjacent cranial nerve functions can cause severe morbidity. To manage such operative risks, a combined supra- and infra-sellar approach(CSISA)can be used as a surgical option for difficult-to-resect large/giant pituitary adenomas. We successfully performed a single-stage CSISA in two patients with large recurrent pituitary adenomas with favorable outcomes. Both patients had recurrent adenomas after multiple trans-sphenoidal surgeries and presented with visual impairment due to tumor regrowth. Each tumor had a maximum diameter of more than 4 cm. One tumor extended into the anterior skull base, while the other extended into the supra-sellar region with extremely lateral invasion. The CSISA helped surgeons visualize the tumors and the surrounding structures through a combination of different operative views. Subtotal resection was safely achieved in both cases, with no postoperative hemorrhage and deterioration of visual and pituitary function. The CSISA is useful not only for pituitary adenomas with anterior or lateral extension and multi-lobular growth, but also for certain cases with recurrent large/giant pituitary adenomas.

Intramedullary spinal cord abscess and subsequent granuloma formation: a rare complication of vertebral osteomyelitis detected by diffusion-weighted magnetic resonance imaging.

An intramedullary spinal cord abscess, which is usually associated with discitis, is an uncommon but potentially important complication of vertebral osteomyelitis. The authors describe a rare case of an intramedullary conus medullaris abscess and lumbar osteomyelitis sparing the intervertebral discs and without discitis. The patient also developed a granuloma in the cauda equina during treatment. Diffusion-weighted MRI was useful for differentiating the granulomatous lesion from the relapse of infection. A 65-year-old immunocompetent man with moderately controlled diabetes presented with progressive lowerextremity numbness and weakness with urinary dysfunction. He had progressive paraparesis, bilateral leg paresthesia, and sphincter compromise. Magnetic resonance imaging revealed an intramedullary ring-enhanced lesion, which was hyperintense on diffusion-weighted images. The lesion, an intramedullary spinal cord abscess, was surgically drained. During antibiotic treatment, serial MRI showed an enlarging enhanced lesion in the cauda equina, and a recurrent infection was suspected. A second-look surgery confirmed the formation of a granuloma and the absence of a relapse of the abscess. Although the enhanced lesion increased in size, its intensity on diffusion-weighted images remained unchanged. After 3 months of antibiotic treatment, all enhanced lesions were diminished. An intramedullary spinal cord abscess is a rare but important complication of vertebral osteomyelitis, and it requires immediate treatment. Diffusion-weighted MRI was useful for the initial diagnosis as well as for monitoring treatment efficacy.

Exoscopic microvascular decompression for hemifacial spasm and trigeminal neuralgia.

The 4K 3D exoscope system is becoming increasingly used in neurosurgery. Its 3D ultra-high-definition image is valuable in identifying and dissecting the delicate neural and vascular structures during microvascular decompression. In this video, the authors describe several nuances and details to perform the exoscopic microvascular decompression, including the exoscope layout and the modified supine position. Several illustrative case presentations highlight the benefits of exoscopic surgery. The authors' exoscopic microvascular decompression series of 159 patients showed noninferior surgical outcomes compared to the operative microscope with no significant increase in surgical risk. In conclusion, an exoscope can be a practical alternative to performing microvascular decompression. The video can be found here: https://stream.cadmore.media/r10.3171/2023.10.FOCVID23122.

Quantitative susceptibility mapping and a nonlinearly transformed atlas for targeting the ventral intermediate nucleus of the thalamus in a patient with tremor and thalamic hypertrophy: illustrative case.

BACKGROUND: The ventral intermediate nucleus (Vim) of the thalamus is a surgical target for treating various types of tremor. Because it is difficult to visualize the Vim using standard magnetic resonance imaging, the structure is usually targeted based on the anterior and posterior commissures. This standard targeting method is practical in most patients but not in those with thalamic asymmetry. The authors examined the usefulness of quantitative susceptibility mapping (QSM) and transformed Vim atlas images to estimate the Vim localization in a patient with tremor and significant thalamic hypertrophy. OBSERVATIONS: A 51-year-old right-handed female had experienced a predominant left-hand action tremor for 6 years. Magnetic resonance imaging showed significant hypertrophy of the right thalamus and caudal shift of the thalamic ventral border. The authors referred to the QSM images to localize the decreased susceptibility area within the lateral ventral thalamic nuclei to target the Vim. In addition, the nonlinearly transformed Vim atlas images complemented the imaging-based targeting. The radiofrequency thalamotomy at the modified Vim target relieved the tremor completely. LESSONS: A combination of QSM and nonlinear transformation of the thalamic atlas can be helpful in the targeting method of the Vim for tremor patients with thalamic asymmetry.

Risk of Bone Wax Migration During Retrosigmoid Craniotomy for Microvascular Decompression: Case-Control Study.

BACKGROUND AND OBJECTIVES: Bone wax is a flexible hemostatic agent commonly used for surgery in the posterior cranial fossa to control bleeding from the mastoid emissary vein. A large amount of bone wax can migrate into the sigmoid sinus through the mastoid emissary canal (MEC). We aimed to identify clinical factors related to intraoperative bone wax migration through the MEC during microvascular decompression (MVD) surgery, which may result in sigmoid sinus thrombosis. METHODS: We retrospectively collected the clinical data of patients with trigeminal neuralgia, hemifacial spasm, or trigeminal neuralgia accompanied by painful tic convulsif who underwent MVD. Basic information and the residual width and length (from the bone surface to the sigmoid sinus) of the MEC on computed tomography images were collected. We compared the collected clinical data between 2 groups of cases with and without intraoperative bone wax migration in the sigmoid sinus. RESULTS: Fifty-four cases with intraoperative bone wax migration and 187 patients without migration were enrolled. The t -test revealed significant differences in the width and length of the MEC ( P = .013 and P = .003, respectively). These variables were identified as significant factors in predicting intraoperative bone wax migration using multivariate logistic regression analysis. CONCLUSION: The large size of the MEC may be related to intraoperative bone wax migration into the sigmoid sinus in MVD. Neurosurgeons should be aware of these risks. Bone wax should be applied appropriately and hemostasis should be considered to control bleeding from the mastoid emissary vein in patients with a large MEC.