Intra- and extracranial solitary fibrous tumor of the trigeminal nerve: CT and MR imaging appearance.

We describe a rare case of SFT existing along the mandibular division of the trigeminal nerve and extending down into the infratemporal fossa through the foramen ovale. The tumor showed heterogeneous hypointensity on T2-weighted images and marked enhancement on CT and MR images.

Hearing preservation and intraoperative auditory brainstem response and cochlear nerve compound action potential monitoring in the removal of small acoustic neurinoma via the retrosigmoid approach.

OBJECTIVE: Hearing preservation is the main focus of small acoustic neurinoma (AN) removal. Refinement of intraoperative auditory monitoring may improve postoperative hearing. We have introduced a newly designed intracranial electrode enabling continuous monitoring of the cochlear nerve compound action potential (CNAP). We performed simultaneous monitoring of the auditory brainstem response (ABR) and CNAP during retrosigmoid small AN removal, and clarified the surgical outcome and the usefulness of CNAP monitoring. METHODS: Twenty-two consecutive patients with a small AN underwent retrosigmoid tumour removal with attempting hearing preservation. ABR and CNAP were simultaneously monitored during tumour removal. RESULTS: AN was totally removed in all patients without facial palsy. Preservation rate of useful and serviceable hearing was 82% and 91%, respectively. During microsurgical tumour removal, various surgical equipments and procedures intensified artefacts of ABR, and reliable ABR monitoring with distinct wave V was obtained in 9/22 patients. Unaffected by artefacts, reliable CNAP monitoring was obtained more frequently (in 20/22 patients) than ABR (p = 0.0005). CNAP on completion of tumour removal predicted hearing preservation with no false positive or negative (100% sensitivity and 100% specificity). CNAP changed dynamically and stepwise with surgical manipulations. CONCLUSION: The retrosigmoid approach using auditory monitoring for a small AN can accomplish total tumour removal with an excellent hearing preservation rate. CNAP provides reliable auditory monitoring more frequently than ABR, reflects the intraoperative auditory function almost in real-time, predicts postoperative hearing with excellent sensitivity and specificity, and is more useful for monitoring in the removal of small AN with hearing preservation.

Removal of large acoustic neurinomas (vestibular schwannomas) by the retrosigmoid approach with no mortality and minimal morbidity.

OBJECTIVE: To evaluate the safety and efficacy of removing large acoustic neurinomas (> or =3 cm) by the retrosigmoid approach. METHODS: Large acoustic neurinomas (mean (SD), 4.1 (0.6) cm) were removed from 50 consecutive patients by the retrosigmoid suboccipital approach while monitoring the facial nerve using a facial stimulator-monitor. Excision began with the large extrameatal portion of the tumour, followed by removal of the intrameatal tumour, and then removal of the residual tumour in the extrameatal region just outside the porus acusticus. The last pieces of tumour were removed by sharp dissection from the facial nerve bidirectionally, and resected cautiously in a piecemeal fashion. RESULTS: There were no postoperative deaths. The tumour was removed completely in 43 of 50 patients (86%). The facial nerve was anatomically preserved in 92% of the patients and 84% had excellent facial nerve function (House-Brackmann grade 1/2). One patient recovered useful hearing after tumour removal. Cerebrospinal fluid leak occurred in 4%, but there were no cases of meningitis. All but two patients (96%) had a good functional outcome. CONCLUSIONS: The method resulted in a high rate of functional facial nerve preservation, a low incidence of complications, and good functional outcomes, with no mortality and minimal morbidity. Very favourable results can be obtained using the retrosigmoid approach for the removal of large acoustic neurinomas.

Potential role of the anterior spinal artery in preventing propagation of thrombus in a therapeutically occluded vertebral artery: angiographic studies before and after endovascular treatment.

Therapeutic occlusion of the vertebral artery (VA) is one of the treatments for unclippable aneurysms and other lesions, although controversy still surrounds the appropriate site for occlusion to attain selective thrombosis of the lesion while avoiding ischaemic complications. The lower two-thirds of the lateral medulla are supplied by perforating branches of both the VA and the posterior inferior cerebellar artery (PICA). However, in patients without a PICA or in whom the origin of the PICA is low (at or below the foramen magnum), the VA is usually the only source of perforating vessels. We retrospectively studied the results of VA occlusion on such anatomically high-risk patients, and propose a safer procedure. Five high-risk patients underwent therapeutic occlusion of the VA for dissecting aneurysms or arteriovenous fistula. A lateral medullary syndrome developed due to propagation of thrombus after the procedure in two patients in whom angiography did not demonstrate the anterior spinal artery (ASA) within the stump of the VA. Ischaemic signs did not develop in the other three patients, in whom the ASA was visible, and retrograde flow was observed proximal to the origin of the ASA. This suggests that the ASA may play a role in preventing propagation of thrombus in the VA distal to the site of occlusion and supply blood to its perforating arteries in high-risk patients. Angiographic assessment of the ASA may be useful for predicting the likelihood of the lateral medullary syndrome developing with therapeutic occlusion of the VA in patients without a PICA or with one whose origin is low.

Diffuse white matter changes caused by dural arteriovenous fistula.

We present two patients with progressive dementia who showed diffuse white matter changes on magnetic resonance imaging (MRI) associated with dural arteriovenous fistula (DAVF) involving the transverse-sigmoid sinuses. Angiography of both patients revealed that DAVF was associated with multiple occlusive changes in the dural venous sinus. The associated occlusive changes isolated the straight sinus and the DAVF from the other venous sinuses, and concentrated the drainage of the DAVF in the straight sinus. We postulate that the venous hypertension of the straight sinus resulted in the venous ischemia of the white matter, diffuse white matter changes on MRI, and progressive neurological signs including dementia. Treatment of the DAVF reversed white matter changes and neurological signs. Associated with the venous sinus occlusions, the DAVF caused dementia with diffuse white matter changes due to the venous ischemia.

Preoperative assessment of trigeminal neuralgia and hemifacial spasm using constructive interference in steady state-three-dimensional Fourier transformation magnetic resonance imaging.

Results of microvascular decompression (MVD) for trigeminal neuralgia (TN) and hemifacial spasm (HFS) may be improved by accurate preoperative assessment of neurovascular relationships at the root entry/exit zone (REZ). Constructive interference in steady state (CISS)-three-dimensional Fourier transformation (3DFT) magnetic resonance (MR) imaging was evaluated for visualizing the neurovascular relationships at the REZ. Fourteen patients with TN and eight patients with HFS underwent MR imaging using CISS-3DFT and 3D fast inflow with steady-state precession (FISP) sequences. Axial images of the cerebellopontine angle (CPA) obtained by the two sequences were reviewed to assess the neurovascular relationships at the REZ of the trigeminal and facial nerves. Eleven patients subsequently underwent MVD. Preoperative MR imaging findings were related to surgical observations and results. CISS MR imaging provided excellent contrast between the cranial nerves, small vessels, and cerebrospinal fluid (CSF) in the CPA. CISS was significantly better than FISP for delineating anatomic detail in the CPA (trigeminal and facial nerves, petrosal vein) and abnormal neurovascular relationships responsible for TN and HFS (vascular contact and deformity at the REZ). Preoperative CISS MR imaging demonstrated precisely the neurovascular relationships at the REZ and identified the offending artery in all seven patients with TN undergoing MVD. CISS MR imaging has high resolution and excellent contrast between cranial nerves, small vessels, and CSF, so can precisely and accurately delineate normal and abnormal neurovascular relationships at the REZ in the CPA, and is a valuable preoperative examination for MVD.

Prevention of cerebrospinal fluid leakage and delayed loss of preserved hearing after vestibular schwannoma removal: reconstruction of the internal auditory canal in the suboccipital transmeatal approach--technical note.

The suboccipital transmeatal approach uses packing of a muscle or fat graft into the internal auditory canal (IAC) to prevent postoperative cerebrospinal fluid (CSF) leakage. However, preserved hearing after removal of vestibular schwannomas may decline over time because of the progressive constriction of cochlear vascular supply due to scarring of the IAC. We propose a surgical technique for IAC reconstruction, which separates the preserved cochlear nerve and vasculature from the graft, and regains the CSF space in the IAC. Prior to the drilling of the posterior wall of the IAC, the dura mater of the petrous bone forming the posterior wall of the IAC is harvested for IAC reconstruction. After completion of tumor removal, a "roof" of the IAC is reconstructed using the dura mater, and a muscle or fat graft soaked with fibrin glue is placed on the "roof" of the IAC. The IAC was reconstructed using this technique in 26 consecutive patients with vestibular schwannomas who underwent tumor removal via the suboccipital transmeatal approach. Postoperative magnetic resonance imaging confirmed the regained CSF space in the IAC. No delayed hearing loss occurred in four patients with preserved hearing. No CSF leakage occurred after surgery. This new technique of IAC reconstruction may prevent delayed hearing loss as well as postoperative CSF leakage after removal of vestibular schwannomas via the suboccipital transmeatal approach.

Detection of Unstable Plaques in Patients with Carotid Stenosis using B-Mode Ultrasonography.

SUMMARY: Distal embolism is a detrimental complication of stent placement for the carotid artery stenosis. To evaluate usefulness of B-mode ultrasonography (US) for the detection of unstable plaques in patients with carotid artery stenosis, we examined US in 46 arteries of 35 patients with carotid stenosis of > 30%. The echogenicity of 46 carotid plaques was hyperechoic in 20 plaques, hypoechoic in 15, and mixed-echoic in 11. The echogenicity of carotid plaques was correlated with severity of carotid stenosis, ipsilateral stroke or TIA, heart attack, and risk factors of systemic atherosclerosis. Hypoechoic plaques were associated with severe carotid stenosis and ipsilateral ischemic event. Mixed-echoic plaques had a high incidence of past history of heart attack. Hyperechoic plaques were less likely to associate with risk factors of systemic atherosclerosis. We developed a new method of echodensity analysis. Using a computer software, echodensity values of seven plaque components were determined by comparing US findings and pathology of surgical specimens. The echodensity value was defined as a relative value to the arterial lumen. The calcified part of plaques had the highest echodensity of 6.24 +/- 0.86 (mean +/- 2 S.D.); fibrosis or hyarynoid degeneration of 2.05 +/- 0.40, foamy histiocytes of 1.47 +/- 0.05, necrosis of 1.32 +/- 0.16, cholestelin clefts of 1.28 +/- 0.13, intraplaque hemorrhage of 1.02 +/- 0.09, and intraluminal thrombus of 1.27 +/- 0.07. Constructed from the echodensity value, an echo-densitometry color mapping of the carotid plaque illustrated the exact location and extent of plaque component. B-mode US of carotid plaques represents clinical characteristics relating distal embolism and systemic atherosclerosis. A new method of echodensity analysis and echo-densitometry color mapping of the carotid plaque is useful to detect unstable plaques in patients with carotid stenosis.

Isolated metastases of adenocarcinoma in the bilateral internal auditory meatuses mimicking neurofibromatosis type 2--case report.

A 56-year-old male with a history of lung cancer presented with isolated metastases of adenocarcinoma in the bilateral internal auditory meatuses (IAMs), mimicking the bilateral acoustic schwannomas of neurofibromatosis type 2, and manifesting as rapidly worsening tinnitus and bilateral hearing loss. Magnetic resonance imaging showed small tumors in both IAMs with no sign of leptomeningeal metastasis. The preoperative diagnosis was neurofibromatosis type 2. Both tumors were removed and the histological diagnoses were adenocarcinoma. Neuroimaging differentiation of a solitary metastatic IAM tumor from a benign tumor is difficult, although rapidly progressive eighth cranial nerve dysfunction suggests a malignant process. Metastases should be considered as a rare diagnostic possibility in a patient with small tumors in both IAMs.

[Location of primary somatosensory area in cerebral arteriovenous malformation involving sensorimotor area].

The purpose of this study was to investigate the cortical reorganization associated with congenital brain lesion such as intracerebral arteriovenous malformation (AVM). Dipole source localization of somatosensory evoked potential (SEP) was performed in five patients with AVM encompassing sensorimotor cortex. Dipole tracing method combined with the scalp-skull-brain head model (Homma et al., 1994) was used to locate dipole source of an early cortical component of SEP elicited by median nerve electrical stimulation. The location of dipole source of SEP, which could be considered as the hand area of primary somatosensory area, was shown in the realistic section of the head and could be easily superimposed on the magnetic resonance imaging. SEP was recorded three times in each patients and the results were reproducible. In 2 patients whose postcentral gyrus was not involved in AVM, the dipole source of SEP was localized in the intact postcentral gyrus. The locations of dipole sources of SEP in the both hemisphere were symmetrical. In 3 patients whose postcentral gyrus was encompassed by AVM, the dipole source of SEP was localized in the surrounding intact gyrus which was distant from the usual region of postcentral gyrus. Somatotopy was different from the normal pattern. The hand area was located more medially than usual observed in normal postcentral gyrus. Despite the paucity of the number of patients and data obtained by dipole source localization, our findings support the existence of reorganization in the cerebral cortex with congenital lesion such as AVM. These findings of aberrant mapping of cortical function may be explained by the plasticity of brain function. The developing brain can inherit function that would normally have been performed by the region of brain involved in the lesion. We demonstrated that dipole tracing of SEP was a noninvasive method used to localize areas of eloquent cortex in patients harboring AVM. This method is of value in treatment planning.

Outcome of traumatic optic neuropathy. Comparison between surgical and nonsurgical treatment.

34 patients with indirect traumatic optic neuropathy were studied to identify factors affecting outcome and surgical indications. 12 cases (13 eyes = group A) underwent surgery and 24 patients (24 eyes = group B) were managed without surgery. Age, optic canal fracture, visual acuity before treatment (initial visual acuity) and days until surgery (only group A) were employed as variables. Visual acuity improved significantly more in patients with initial visual acuity, hand movement (HM) or better than in those with initial visual acuity for light perception (LP) only or worse. When initial visual acuity was HM or better, vision improved significantly more in patients with surgery than in those without surgery (p = 0.0003 by Mann-Whitney U test). Days until surgery were correlated with visual improvement in patients with visual acuity HM or better. Age and optic canal fracture did not affect visual improvement or influence the decision for or against surgery.

Recovery of hearing after removal of a large jugular foramen schwannoma: report of two cases.

BACKGROUND: Although hearing loss is a common presenting symptom of jugular foramen schwannoma (JFS), recovery of hearing after tumor removal has rarely been reported. We report two cases of a large JFS presenting with severe hearing loss and recovering normal hearing after tumor removal. METHODS AND RESULTS: Two patients complaining of progressive hearing loss each proved to have a large JFS involving the posterior fossa. The hearing losses, which exceeded 90 dB, were not associated with dysfunction of the 9th, 10th, or 11th cranial nerves. Schwannomas were removed by a suboccipital retrosigmoid approach, preserving labyrinthine structures. The vestibulocochlear nerve, stretched and displaced rostrally by the tumor, was preserved with surrounding arachnoidal tissue. Soon after surgery, recovery of hearing began; normal hearing was restored within 3 months. CONCLUSIONS: In a case of JFS with severe hearing loss, normal hearing may be attainable by tumor removal using a retrosigmoid approach that preserves labyrinthine structures. The arachnoidal tissue separating the vestibulocochlear nerve from the schwannoma is important to hearing preservation.

Angioarchitecture predicting hemorrhage in cerebral arteriovenous malformations.

To find out lesions responsible for hemorrhage in arteriovenous malformations (AVMs), a retrospective study of angioarchitecture around the nidus was conducted in 27 patients who underwent conservative treatment. Comparison of angiograms revealed disappearance of an intranidal aneurysmal dilatation after the hemorrhagic events in two cases. The hematomas were adjacent to the dilatation, and no subarachnoid hemorrhage was evident. Obstruction of venous drainage, noticed in a case of spontaneous regression of AVM, was not demonstrated in the cases of hemorrhage. The intranidal aneurysmal dilatation is likely to have caused the hemorrhage in our cases. Careful endovascular embolization using proper materials should be indicated for an intranidal aneurysmal dilatation to prevent subsequent hemorrhage.

[Venous system playing a key role in transpetrosal approach].

A case with a large vertebrobasilar junction aneurysm developed a venous infarction in the temporal lobe after an operation using the transpetrosal approach. Although little of the literature has been concerned with venous complications after the transpetrosal approach, the case prompted us to study the venous system as playing a key role in the transpetrosal approach. Analyzing 30 carotid and 15 vertebral angiograms of 15 patients who underwent preoperative cerebral angiography using digital subtraction angiography (DSA), we investigated the venous system near the junction of the superior petrosal sinus, the transverse sinus and the sigmoid sinus (STS junction) which may play a key role in the transpetrosal approach. Drainage pathways of the superficial middle cerebral vein (SMCV) were classified into four types; sphenoparietal, sphenobasal, sphenopetrosal and undeveloped. In the sphenopetrosal type (4/30: 13%), the drainage of SMCV passes back along the floor of the middle fossa to drain into the transverse sinus. The lateral temporal vein (LTV) and the temporobasal vein (TBV) drain into the transverse sinus. The LTV emptied into the transverse sinus either directly (20/30: 67%) or indirectly through the tentorial sinus (10/30: 33%). The entry of the LTV into the transverse sinus (venous point) was usually located in the lateral third of the transverse sinus (14/20: 70%), but sometimes in the middle third (6/20: 30%). The TBV, observed in 8/30 (27%), also often emptied into the tentorial sinus to drain into the transverse sinus. Atresia of a unilateral transverse sinus and a large LTV emptying into the distal sigmoid sinus was observed in 2/15 cases. The venous system near the STS junction may be interrupted by the incision of the tentorium and the middle fossa dura mater and by the retraction of the sigmoid sinus. Since the transpetrosal approach may cause venous complication by compromising the venous system near the STS junction, it is necessary to evaluate of the venous system preoperatively using DSA and to set up a surgical strategy preserving the venous system.

Sigmoid sinus dural arteriovenous malformation resulting from jugular foramen schwannoma--case report.

A 69-year-old male presented with a jugular foramen schwannoma occluding the sigmoid sinus and associated with sigmoid sinus dural arteriovenous malformation. The patient presented with dizziness and pulsatile tinnitus following an extended period of hearing loss beginning several years before. Both lesions were resected successfully after transarterial embolization of the malformation. The sequence of symptom development suggests the dural sinus thrombosis caused the dural arteriovenous malformation.

Angioarchitecture related to hemorrhage in cerebral arteriovenous malformations.

A retrospective study was conducted to determine the angioarchitecture related to hemorrhage in patients with cerebral arteriovenous malformations (AVMs), who underwent conservative treatment and long-term follow-up. The average observation period was 9.3 years, and the annual bleeding rate was estimated at 3.6%. In all cases angiographic findings were reviewed in detail. The average AVM grade by Spetzler-Martin was 3.5. Higher bleeding rate was observed in large AVM (5.4%) compared with small (2.1%) or medium AVM (2.9%). Deep venous drainage (8.6%/year) was strongly correlated to hemorrhage. Concerning location of nidus, hemorrhage was frequently found in insular, callosal, and cerebellar AVMs. Venous ectasia, feeder aneurysm, and external carotid supply were commonly demonstrated on angiograms. Comparison of annual bleeding rate revealed that AVMs with intranidal aneurysm (8.5%) and venous stenosis (5.5%) had a high propensity to hemorrhage. Therapeutic strategy should be focused on these potentially hazardous lesions by the use of endovascular embolization or stereotactic radiosurgery, even if surgical resection is not indicated.

Endovascular embolisation of a cerebral arteriovenous fistula with hereditary haemorrhagic telangiectasia. Case report and review of the literature.

SUMMARY: We report a case of cerebral arteriovenous fistula (AVF) associated with hereditary haemorrhagic telangiectasia (HHT). Although the patient had no symptoms from the cerebral AVF, the AVF was successfully embolised using a twostaged double provocative test. We reviewed the literature of HHT and have concluded that there are two types of cerebral arteriovenous communication in patients with HHT and endovascular embolisation is the most reasonable therapy for the fistula type from the standpoint of its angioarchitecture.

[Dural arteriovenous malformation presenting venous ischemia].

We report three patients with dural arteriovenous malformation (DAVM) in the posterior fossa presenting the venous ischemia and the pathophysiology and the clinical characteristics of DAVM presenting the venous ischemia are discussed. Associated with occlusive changes in the venous sinuses, DAVM in the posterior fossa develops the venous hypertension of the straight sinus and the venous ischemia of cerebral white matter and basal ganglia. The venous ischemia presents progressive symptoms consisting of dementia with or without the ensuing consciousness disturbance. Multiple parenchymal lesions and abnormally dilated and tortuous veins are the characteristic findings in MRI/CT.

[Acoustic neurinoma located exclusively in cerebellopontine angle cistern ("cisternal" acoustic neurinoma): a case report].

This is a case report of acoustic neurinoma which was located exclusively in the cerebellopontine angle (CPA) cistern and which did not extend into the internal auditory meatus ("cisternal" acoustic neurinoma). The 43-year-old female patient had signs of the left trigeminal nerve impairment including left face neuralgia. However, she did not have any neurootological symptom. No abnormal bony changes in the internal auditory meatus (IAM) were found by high-resolution bone-window CT. MRI showed a left CPA tumor of 25mm not extending into the IAM. The tumor was totally removed by the lateral suboccipital approach. It originated from the vestibular nerve medial to the porus acusticus and was located exclusively in the CPA cistern. No tumor extension into the IAM was confirmed. The cochlear nerve was involved in the tumor capsule and could not be preserved. The pathological diagnosis was that it was a neurilemmoma. Early diagnosis of "cisternal" acoustic neurinoma is difficult because it does not show neurootological symptoms in the early stage. The lateral suboccipital approach is appropriate for the removal of a "cisternal" acoustic neurinoma. However, in spite of the good preoperative hearing, the preservation of hearing is difficult because of the large tumor size.