Distal Mycotic Aneurysm of the AICA Mimicking Intracanalicular Acoustic Neuroma

Background:

Among cases of cerebellopontine angle lesions, vascular lesions involving the internal auditory canal are extremely rare. We report a distal fusiform mycotic pseudoaneurysm of the anterior inferior cerebellar artery (AICA) that simulated an acoustic neuroma on presentation.

Methods:

A 60-year-old woman was investigated for recent onset of acute dizziness. Laboratory and radiographic investigations are presented, as well as the surgical management of the patient and pathological examination of the aneurysm.

Conclusion:

An exceptionally rare case of distal mycotic intracanalicular pseudoaneurysm of the AICA with intraluminal thrombus and fusiform anatomy is described. In our review of the literature (1966-present), only five other intracanalicular AICA-aneurysms were encountered, none of which were infectious in etiology. The possible pathophysiologic mechanisms of distal AICA-aneurysms are discussed along with the currently available literature.

Imaging-documented repeated intratumoral hemorrhage in vestibular schwannoma: a case report

Intratumoral hemorrhage in vestibular schwannomas is rare. Symptoms often have an acute onset and include headache, nausea, vomiting, vertigo, and depressed consciousness. Intratumoral hemorrhage is probably caused by vascular fragility associated with tumor characteristics and growth. With hemorrhage in VS being rare, repeated hemorrhage has only been reported twice, and on clinical grounds only. The present report details the case of acute neurological deterioration in a patient with repeated intratumoral hemorrhage inside a vestibular schwannoma with computed tomography and magnetic resonance imaging confirmation. To our knowledge, repeated hemorrhage in vestibular schwannoma with radiological confirmation has not been reported before.

Expression of vascular endothelial growth factor and basic fibroblast growth factor in sporadic vestibular schwannomas correlates to growth characteristics

HYPOTHESIS

Expression of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) may have an impact on the growth characteristics of sporadic vestibular schwannomas (VSs).

BACKGROUND

Vestibular schwannoma is a benign, slow-growing neoplasm that accounts for 6% of all intracranial tumors. The biological backgrounds for neoplastic growth and especially for the various growth patterns of VS remain largely unknown. Because several angiogenic and cytotrophic factors have been described to be involved in the growth of malignant tumors, we initiated this study to examine 2 major representatives of such growth factors in VS and their possible correlation to the growth characteristics of sporadic VSs.

METHODS

Surgical specimens from 17 patients with sporadic VS were examined, and the expression of 2 major angiogenic and neurotrophic factors, bFGF and VEGF, was quantitatively analyzed at the mRNA and protein levels. The microvessel density (MVD) was defined by CD31 staining.

RESULTS

All tumors showed expression of bFGF and VEGF at both the mRNA and protein levels. The mRNA expression and the protein expression of both growth factors correlated positive to tumor volume, to tumor growth index, and to MVD.

CONCLUSION

The bFGF and VEGF mRNA expression and the bFGF and VEGF protein expression in sporadic VS correlates to the tumour volume, to the tumor growth index, and to the MVD. This might indicate an angiogenic and neurotrophic influence of these factors and a possible involvement in the growth of sporadic VS.

Microhemorrhage, a possible mechanism for cyst formation in vestibular schwannomas

OBJECT

Cystic vestibular schwannoma (VS) is a unique subgroup of VSs characterized by unpredictable expansion of the cyst component. Little is known, however, about the mechanism of cyst formation. In this study the authors compared neuroimaging and histological characteristics of cystic with solid VS to determine the pathogenesis of the cystic subgroup.

METHODS

Two cohorts, one comprising 10 patients with cystic VS and the other comprising 10 patients with solid VS, were studied. Surgery was chosen as the primary treatment in all patients, with no other modality applied. Preoperative magnetic resonance images and histological characteristics of the tumor in patients with cystic VSs were evaluated and compared with those in the group with solid VSs. Differences between the two groups were assessed using the chi-square test. Neuroimaging findings revealed that either fluid-fluid level or hemosiderin deposit was present in all cystic VSs. Histological evidence of microhemorrhage, such as hemosiderin-laden macrophages (p = 0.069), hemosiderin deposits (p = 0.019), thrombotic vessels (p = 0.008), and abnormal vessel proliferation (p = 0.006) were more prominent in cystic VSs compared with solid ones. There was no difference in Antoni type dominance and Ki-67 proliferative index between the two groups.

CONCLUSIONS

Intratumoral microhemorrhage is a possible mechanism of pathogenesis in cystic VS.

alpha(v)beta(3) Integrin in central nervous system tumors

alpha(v)beta(3) Is an integrin specifically expressed in endothelial cells of newly forming blood vessels. Integrin-mediated angiogenesis is hypothesized to play a central role in the development and the progression of central nervous system neoplasms. Accordingly, it is considered a potential target for antiangiogenic therapy. In the current study, we compare the expression of alpha(v)beta(3) in ependymomas, oligodendrogliomas, pilocytic astrocytomas, medulloblastomas, and vestibular schwannomas (acoustic neuromas). Samples of 5 tumors of each of the 5 tumor types were harvested surgically and frozen. After the pathological diagnosis was confirmed, immunohistochemistry was performed using an anti- alpha(v)beta(3) monoclonal antibody (LM609). The expression of alpha(v)beta(3) was assessed using a 4-tiered (0-3) grading scheme reflecting the percentage of positively staining vessels. All vestibular schwannomas demonstrated strong (grade 3) alpha(v)beta(3) expression. The expression was uniformly prominent in Antoni B regions of the tumors. Of 5 ependymomas, 4 demonstrated uniformly strong alpha(v)beta(3). Oligodendrogliomas, medulloblastomas, and pilocytic astrocytomas demonstrated more variable alpha(v)beta(3). alpha(v)beta(3) may contribute significantly to angiogenesis in vestibular schwannomas and ependymomas. Despite the high vascular density of oligodendrogliomas, pilocytic astrocytomas, and medulloblastomas, these tumors had variable moderate alpha(v)beta(3) expression. This discrepancy suggests temporal and/or regional variability in the angiogenesis in these types of tumor. This study provides the first demonstration of alpha(v)beta(3) expression in vestibular schwannomas, medulloblastomas, and pilocytic astrocytomas.

VEGF and VEGF receptor-1 concentration in vestibular schwannoma homogenates correlates to tumor growth rate

OBJECTIVE

Vascular endothelial growth factor (VEGF) is one of the most potent mediators of angiogenesis, which is a mandatory process during tumor growth. Immunohistochemical studies have demonstrated VEGF expression in vestibular schwannomas (VS), and a semi-quantitation of staining intensity indicated a correlation between tumor growth rate and VEGF expression. The present objectives were to determine the concentration of VEGF and the high-affinity receptor VEGFR-1 in VS homogenates and to examine a possible correlation with symptom duration, tumor size, or growth rate.

STUDY DESIGN, PATIENTS, AND METHODS

Prospective selection of 27 patients with VS growth determined by repeated magnetic resonance imaging. Patient files were reviewed for symptom duration and all magnetic resonance images reviewed for determination of tumor size and growth rate. ELISA was used for determination of the VEGF and VEGFR-1 concentration in tumor homogenates.

SETTING

Tertiary University Hospital Clinic.

RESULTS

All tumor homogenates contained VEGF and VEGFR-1. A significant correlation existed between the concentration of both VEGF and VEGFR-1 and tumor growth rate but not symptom duration or tumor size.

CONCLUSION

The concentration of VEGF and VEGFR-1 in VS homogenates correlates with tumor growth rate but not with tumor size or symptom duration. We conclude that VEGF and VEGFR-1 appear to be directly involved in the growth pattern of VS.

The immunohistochemical localisation of somatostatin receptors 1, 2, 3, and 5 in acoustic neuromas

AIMS

Acoustic neuroma is a benign tumour, which develops through an overproliferation of Schwann cells along the vestibular nerve. Somatostatin is a naturally occurring peptide, which exerts antiproliferative and antiangiogenic effects via five membrane bound receptor subtypes. The aim of this study was to determine whether somatostatin receptor subtypes (SSTRs) 1, 2, 3, and 5 are present in acoustic neuromas.

METHODS

The expression of SSTRs 1, 2, 3, and 5 was studied in both the Schwann cells and blood vessels of eight acoustic neuroma specimens, by means of immunohistochemistry using novel rabbit polyclonal antibodies raised against human SSTR 1, 2, and 5 subtype specific peptides, and a commercial anti-SSTR3 antibody.

RESULTS

SSTR2 was the most prevalent subtype in Schwann cells (seven of eight), with intermediate expression of SSTR3 (six of eight), and lower expression of SSTRs 1 and 5 (four of eight and five of eight, respectively). There was ubiquitous vascular expression of SSTR2, with no evidence of SSTR 1, 3, or 5 expression in blood vessels.

CONCLUSION

SSTRs 1, 2, 3, and 5 are differentially expressed in acoustic neuromas. Somatostatin analogues may have a therapeutic role in the management of this rare and challenging condition.

Hypervascular intracisternal acoustic neuroma

The diagnosis of acoustic neuroma is usually evoked in a patient presenting with a long history of hearing disturbance in whom an enhancing lesion within the internal auditory canal and/or the cerebellopontine angle is found on MRI. Hypervascularity with arteriovenous shunting and early filling of enlarged veins is a common feature of malignancy and has been reported very rarely in benign acoustic neuroma. We present the case of a patient without hearing disturbance, who showed a highly vascular lesion with no component in the internal auditory canal, making the preoperative diagnosis of acoustic neuroma very challenging. We discuss here the intracisternal site of origin and hypervascularity of acoustic neuroma, and also the differential diagnoses and management of such tumors.

Hypervascular vestibular schwannomas

BACKGROUND

Vestibular schwannoma (VS) is usually hypovascular and can be resected totally without major morbidity. Resection of the more uncommon hypervascular VS is complicated by excessive tumor bleeding. We have attempted to clarify the clinical characteristics and management of hypervascular VS.

METHODS

Surgical reports and videos of 78 patients with unilateral VS (5 hypervascular, 73 nonhypervascular) were retrospectively reviewed and clinical characteristics, radiological findings, and case management were compared.

RESULTS

Hypervascular VS presented at a younger age than nonhypervascular VS (29 +/- 12 vs. 52 +/- 16 years old) (p < 0.01). Magnetic resonance imaging (MRI) showed that hypervascular VS was solid, without tumor cyst, and significantly larger than nonhypervascular VS (p < 0.05). The surface of hypervascular VS consistently showed multiple flow voids representing large draining veins. The characteristic angiographical findings of hypervascular VS were extensive tumor vessels, tumor stains, and early filling of draining veins; vertebrobasilar arteries supplied hypervascular VS. A multi-stage surgical approach was used since torrential tumor bleeding in the first surgery interfered with resection, resulting in partial tumor removal. Angiography before the second surgery showed much reduced tumor vascularity, bleeding was much reduced, and tumor was resected with less difficulty. In this approach, all 5 hypervascular VS were resected totally (1 case) or near-totally (4 cases) without major morbidity.

CONCLUSIONS

Hypervascular VS, a solid and large tumor, presents at an earlier age. Although angiography provides characteristic findings, MRI can confirm the diagnosis of a hypervascular VS by showing multiple flow-voids on the tumor surface. Since partial tumor removal (first surgery) extensively reduces tumor vascularity and intraoperative tumor bleeding considerably, hypervascular VS should be managed by a multi-staged surgical approach.

Quantification of endothelial permeability, leakage space, and blood volume in brain tumors using combined T1 and T2* contrast-enhanced dynamic MR imaging

This study describes a method for imaging brain tumors that combines T1-weighted (T1W) and T2*-weighted (T2*W) dynamic contrast-enhanced acquisitions. Several technical improvements have been made to produce high-quality three-dimensional mapping of endothelial permeability surface area product (k) and leakage space (vl), based on T1W data. Tumor blood volume maps are obtained from T2*W images with a complete removal of residual relaxivity effects. The method was employed in 15 patients with brain tumors (5 gliomas, 5 meningioma, and 5 acoustic schwannoma). Mean values of vl were significantly greater in acoustic schwannomas (53% +/- 9%) than in meningiomas (34% +/- 7%) or gliomas (22% +/- 4%). Mean values of vl in meningioma were significantly greater than those of gliomas. Mean values of rCBV correlated closely with k. There was also a positive correlation between k and vl for pixels with low k values. This relationship was weaker in areas of high k. The highest mean ratios of k to vl (k(ep)) were seen in two patients with glioblastoma, one patient with transitional cell meningioma, and one patient with angioblastic meningioma. Pixel-by-pixel comparison showed a strong correlation between rCBV and k in 11 of 15 patients. However, decoupling between pixel-wise rCBV and k was found in four patients who had lesions with moderate k and vl elevation but no increase of rCBV. Results from this study suggest that in assessing the angiogenic activities in brain tumors it is advisable to monitor simultaneously changes in tumor blood volume, vessel permeability, and leakage space of tumor neovasculature.

Vascular permeability: quantitative measurement with double-echo dynamic MR imaging--theory and clinical application

Double-echo dynamic magnetic resonance (MR) imaging was used to evaluate both vascularity and permeability of tissues simultaneously. Vascularity was evaluated on the basis of the T2*-shortening effect due to the intravascular fraction of the contrast agent and permeability on the basis of the T1-shortening effect due to the extravascular fraction. Meningioma was characterized on the basis of higher vascularity and neurinoma on the basis of higher permeability. The proposed method enables better tissue characterization.

Dual origin of the vertebral artery--case report

A 27-year-old female presented with dual origin of the left vertebral artery. Twenty-six cases of this rare congenital vascular anomaly have been reported. In general, the medial leg of the dual origin of the vertebral artery enters a higher transverse foramen (usually the fifth or less frequently the fourth) than the lateral leg, which usually enters the sixth. Exceptions to this rule occur when the medial and lateral legs of the right vertebral artery enter the right seventh and sixth transverse foramina, respectively. This congenital vascular anomaly has diagnostic and therapeutic implications in any intervention involving the proximal vertebral artery.

Three-dimensional phase contrast MR cerebral venography with zero filling interpolation in the slice encoding direction

The purpose of this study was to evaluate the magnetic resonance (MR) cerebral venography findings of a three-dimensional phase contrast MR sequence with zero filling interpolation of the data in the slice encoding direction. Fifty volunteers were enrolled in the study. Images were obtained on a 1.5 MR imaging system with acquisition time of 12 min. MIP images were reconstructed throughout the entire imaging volume. A grading scale system was used to assess dural venous sinuses, major deep veins, cortical, and cortical eponymic veins. Inferior group of dural venous sinuses, inferior sagittal sinus, and cortical eponymic veins were poorly demonstrated. Score of the superior sagittal sinus, the straight sinus, the confluence of the superior sinus group, the right transverse and sigmoid sinuses, the internal veins, and the vein of Galen was excellent. The score of the left transverse and sigmoid sinuses was good. In conclusion, when using zero filling interpolation of the data in a three-dimensional phase contrast MR cerebral venography sequence, the superior group of dural venous sinuses and main major deep veins are demonstrated with good conspicuity.

Measurement of cerebral perfusion with dual-echo multi-slice quantitative dynamic susceptibility contrast MRI

Quantitative cerebral perfusion was measured in vivo using dynamic susceptibility contrast magnetic resonance imaging. A dual-echo acquisition was used to eliminate T(1)-enhancement. The arterial input curve was measured in a separate slice in the neck to minimize partial volume effects. Data analysis was performed using a maximum likelihood expectation maximization method to be less sensitive to noise or contrast arrival time differences. From the contrast response curves obtained, the cerebral blood volume (CBV) and flow (CBF) and the timing parameters mean transit time (MTT), time of appearance (TA), and time-to-bolus peak (TBP) were obtained. Adjacent slices were measured to permit discrimination between intra- and inter-subject variance. The group investigated consisted of 41 subjects without cerebral pathology on anatomical MRI. Perfusion parameters for gray (GM) and white matter (WM) were obtained: CBV (GM) = 6.78 +/- 0.99 ml/100 ml, CBV (WM) = 3.78 +/- 0. 96 ml/100 ml, CBF (GM) = 68.7 +/- 21.2 ml/100 ml/min, CBF (WM) = 35. 8 +/- 12.7 ml/100 ml/min, and average GM/WM ratio for CBV (GM/WM) = 1.87 +/- 0.42 and CBF (GM/WM) = 1.99 +/- 0.48. Measured temporal aspects of perfusion were: mean transit time (MTT) (GM) = 6.4 +/- 1. 8 seconds, MTT (WM) = 6.9 +/- 2.3 seconds, time of appearance (TA) (GM) = 1.4 +/- 0.9 seconds, TA (WM) = 2.0 +/- 1.0 seconds, and time-to-bolus peak (TBP) (GM) = 2.4 +/- 1.4 seconds, TBP (WM) = 3.0 +/- 1.5 seconds. The average values were in agreement with those from the literature. Inter- and intra-person variances were estimated using an ANOVA test, and the sources of variance in the parameters, such as image noise, biological variability, and measurement errors of the arterial input curve were found to be of the same order of magnitude. J. Magn. Reson. Imaging 1999;10:109-117.

[Diagnosis and growth evaluation of vestibular schwannomas by SPECT combined with TL-201 thallium]

The value of SPECT scanning in diagnosis and growth potential of vestibular schwannoma (VS) was investigated in a series of 29 patients. SPECT demonstrated all tumours > 0.8 cm3, but had limitations as a diagnostic modality of small intracanalicular tumours, when compared to gadolinium DTPA enhanced MR. SPECT was found to be valuable in determining VS growth potential as it reflects tumour vascularity, which is essential for tumour growth. A high radioactive tracer uptake in the tumour corresponded to high tumour vascularity, indicating a high growth rate and vice versa. It seems that we now have an in vivo functional radiological modality capable of providing data on VS vascularity and determination of growth potential in the individual tumour.

Hypervascular acoustic neuroma

The authors present a patient with a large acoustic neuroma that exhibited an unusual vascular architecture. Magnetic resonance imaging demonstrated multiple flow voids in and around the mass. At surgery, intra- and extratumoral vascularity was arterialized due to luxurious shunting. Two attempts at removal produced severe engorgement and pulsatility of the surrounding brain, dramatically narrowing the operative exposure. Piecemeal resection of the tumor seemed to redistribute blood flow resulting in engorgement of the surrounding brain, analogous to perfusion breakthrough following AVM resection. Treatment strategies similar to those used for AVM resection may be indicated when encountering a hypervascular tumor.

Hemorrhage and abnormal veins in acoustic neurinoma: MR findings

We reviewed the MR imaging findings of 57 acoustic neurinomas which were verified at surgery or diagnosed on the basis of neuroradiological and neurootological data. Two uncommon MR findings of acoustic neurinoma were found. First, hypointense areas were observed on T2-weighted images in five of the 12 tumors larger than 25 mm in diameter. These hypointense areas represented hemosiderin deposition secondary to occult intratumoral hemorrhage. Second, curvilinear or round signal voids were noted at the periphery of 11 large or medium-sized tumors, and these corresponded to "abnormal veins" seen on angiographic studies.

Effect of Gamma Knife radiosurgery on acoustic neurinomas. Assessment by 99mTc-DTPA-human serum albumin- and 201TlCl-single photon emission computed tomography

Single photon emission computed tomography (SPECT) was performed on 16 patients with acoustic neurinoma before and 1 and 2 years after Gamma Knife surgery. 201TICI-SPECT was used to determine tumor viability. Early and delayed images of 99mTc-DTPA-human serum albumin (99mTc-HSA-D)-SPECT were used to assess tumor vascularity and permeability, respectively. There was a statistically significant decrease in the 99mTc-HSA-D index of the early image at 1 year (p = 0.013) and at 2 years (p = 0.018) after Gamma Knife surgery. On the other hand, the 201Tl index and the 99mTc-HSA-D index of the delayed image were not significantly different from their pretreatment values. These observations demonstrate that a reduction in tumor vascularity without a decrease in tumor viability may be one of the effects of Gamma Knife surgery on acoustic neurinomas.

Vascularity of meningiomas and neuromas: assessment with dynamic susceptibility-contrast MR imaging

OBJECTIVE

Dynamic susceptibility-contrast MR imaging provides hemodynamic information about normal and pathologic tissue of the brain. The purpose of this study was to determine the value of this technique in assessing the vascularity of meningiomas and neuromas.

MATERIALS AND METHODS

Sixteen patients with extraaxial brain tumors (eight meningiomas and eight neuromas) and seven subjects without evident brain lesions were studied with a conventional 1.5-T MR unit. Dynamic susceptibility-contrast MR imaging was done with a gradient-echo technique (33/23/10 degrees [TR/TE/flip angle]) during bolus IV injection of 0.15 mmol/kg gadopentetate dimeglumine. The integral of the rate of change in T2* (integral of delta R2*dt) was calculated and compared among the brain tumors and normal brain.

RESULTS

The mean integral of delta R2*dt value obtained was significantly higher in meningiomas than in neuromas (p < .001), which shows that meningiomas are generally more vascular than neuromas. We found no significant difference in the mean integral of delta R2*dt between neuromas and normal brain regions.

CONCLUSION

Dynamic susceptibility-contrast MR imaging provides information about the degree of the vascularity of meningiomas and neuromas that is not available with conventional MR imaging.

Gliosis of the eighth nerve transitional region in patients with cerebellopontine angle schwannoma

The central-peripheral transitional region (TR) of the eighth nerve root was obtained from 8 patients with cerebellopontine angle schwannoma and investigated by light microscopy, electron microscopy, and immunohistochemistry. As a control, the TRs of 6 autopsy patients without any otologic disease were studied. Astrocytic proliferation at the TR was more prominent in the schwannoma patients than in the normal controls. Mild gliosis of the mantle zone of the TR was found in 5 schwannoma patients and moderate gliosis was noted in 3. The distribution of capillaries at the TR differed between the schwannoma patients and the normal controls. In the schwannoma patients, capillaries were rarely found in the mantle zone of the TR but were densely clustered at the glial fringe zone, especially near its border with the peripheral nervous tissue. Stasis of the capillaries in the glial fringe zone was frequently noted. These histological findings may indicate the occurrence of gliosis in response to eighth nerve degeneration. We suggest that there is increased susceptibility of the eighth nerve to injury at the TR in patients with schwannoma.

Posterior fossa venous anomaly and ipsilateral acoustic neuroma: two cases

The association of an acoustic neuroma with an ipsilateral venous anomaly or angioma is reported in two patients. In the first, the venous angioma was situated low in the posterior fossa, and was of no significance surgically. In the second, the angioma was strongly attached to the capsule of the tumour. On MRI and angiography the lesion appeared as a large draining vein, encircling the tumour. At operation, extensive dissection of the angioma from the neuroma appeared necessary to prevent venous infarction of the brain stem.

Acoustic schwannomas in children

The clinical presentation and treatment of three cases of acoustic schwannoma occurring in children are described. All the tumors were detected late, when they had attained a large size and were extremely vascular. The use of preoperative tumor embolization as an adjunct to surgical excision is discussed.

Massive hemorrhage in acoustic neurinoma after minor head trauma--case report

Massive hemorrhage within an intracranial neurinoma occurs rarely. The authors describe a 62-year-old female with intratumoral bleeding which led to the discovery of an acoustic neurinoma. She developed a gait disturbance after a minor head injury. A computed tomographic scan obtained 2 months later demonstrated multiple high-density areas in the anterior portion of the left cerebellopontine angle. Preoperative diagnosis was acoustic neurinoma. The tumor had multiple cysts which contained a mixture of xanthochromic fluid and old, brownish hematomas, and was successfully removed. The intratumoral hemorrhage is thought to have resulted from traumatic rupture of the dilated vessels, although the trauma was slight. This is the first reported case of an acoustic neurinoma discovered through treatment for intratumoral hemorrhage occurring after a minor head injury.

Growth of human schwannomas in the subrenal capsule of the nude mouse

To develop a reproducible in vivo model for the growth of human schwannomas we implanted tumor specimens from 14 different patients (13 acoustic neurinomas; 1 trigeminal schwannoma) into the subrenal capsule of 108 nude mice. In 11 experiments, the animals were implanted with only solid tumor from the surgical specimens. In two experiments, the tumor implants were made from solid tumors and cell clusters. In one experiment, the tumor implants were made from cell clusters alone. The size and neovascularization of these tumors were serially determined during a 1.5- to 3-month period. The percentages of tumors that survived or grew were 77.3% from solid tumors and 70% from cell clusters. Maximum tumor volume varied as did the time span to reach that volume. Tumor enlargement and stability correlated well with neovascularity; regressing tumor showed minimal or no neovascularity. Histological analysis of the implanted tumors showed spindle cells that are similar to the original tumor. Immunohistochemical staining for S100 demonstrated the Schwann cell nature of the implants. Analysis of genomic DNA from an acoustic neurinoma that had been implanted for 3 weeks was consistent with its human origin. There were no significant microscopic differences among groups receiving solid tumor implants or cell clusters. These studies suggest that implantation of human schwannomas into the subrenal capsule of the nude mouse is a reproducible method to study tumor growth that may be useful in testing potential therapeutic regimens or genetic modulation of schwannomas.

Acoustic neurinoma presenting as intratumoral bleeding

The authors report a case of acoustic neurinoma presenting as intratumoral bleeding. This is the tenth reported occurrence. The literature is reviewed. All cases that have been reported have appeared with sudden onset of headache, vomiting, and decreased levels of consciousness. Aneurysm rupture, an arteriovenous malformation, or other vascular anomalies are suspected first. Preexisting unilateral hearing impairment is a valuable clue to differential diagnosis. Contrast-enhanced computed tomographic scans and cerebral angiograms are important tools for correct diagnosis. The tumor size (greater than 2 cm) and the thin, dilated vessels within the tumor are considered as pathogenetic factors for bleeding. When neurological status is not stable, placement of a ventriculoperitoneal shunt followed by urgent extirpation of the tumor is indicated.

[Acoustic neurinoma presenting with repeated intratumoral hemorrhage. Case report]

A case of acoustic neurinoma with multiple intratumoral hemorrhages is reported. A 56-year-old male noted sudden hearing reduction in his left ear in October of 1985. The diagnosis of a local physician was sudden deafness. About 10 months later, he had two episodes of severe headache without nausea or vomiting. The patient was hospitalized in October of 1986. Neurological examination cerebellar ataxia. cerebellar ataxia. Plain and enhanced computed tomography revealed only an unremarkable low-density area at the left cerebellopontine angle. In contrast, magnetic resonance imaging (MRI) clearly demonstrated a large (3 x 4 x 5 cm), multicystic tumor in the site. On exposure of the tumor at surgery, most of the cysts were found to be filled with a dark red or xanthochromic fluid. The tumor was completely removed following numerous cyst punctures to decrease its volume. There was no evidence of subarachnoid hemorrhage. Histological examination showed a typical acoustic neurinoma. The cyst wall contained numerous telangiectasia-like lesions. The initial symptom of this patient was sudden hearing loss, which is an atypical manifestation of acoustic neurinoma. The massive intratumoral hemorrhage was thought to be caused by telangiectatic lesions in the cyst wall. MRI clearly demonstrated the hemorrhagic cysts within the tumor, especially in the posterior fossa.

Massive hemorrhage into intracranial neurinomas

Massive bleeding into an intracranial neurinoma is a rare event. The 12th case of this particular occurrence, which was precipitated by weight lifting, is described and a review of the literature is presented. Risk factors for bleeding appear to be tumor size and vascularity. Presenting symptomatology is abrupt and includes headache, nausea, vomiting, and depressed consciousness. Preexisting symptoms referrable to and marked dysfunction of the cranial nerve of origin are present. Deficits of neighboring cranial nerves are frequent. Computed tomography demonstrates the hemorrhages and the tumors. Mild head injury and physical exertion were precipitating factors in two cases. One-fourth of the patients died, while the others made good recoveries.

Early venous filling in acoustic schwannoma

An unusual case of acoustic schwannoma in neurofibromatosis with extensive and abundant early draining veins demonstrated on angiography is reported with a brief discussion of the literature. Although the histological features were those of a typical acoustic schwannoma, many dilated and thin-walled vascular channels were interspersed among the tumor.

Ultrastructure of capillaries in acoustic neurilemmoma

The microvasculature of normal acoustic nerve tissue and small intracanalicular and large extracanalicular neurilemmomas was analyzed by electron microscopy. The capillaries of normal acoustic nerve were nonfenestrated, but the microvasculature in nerve-sheath neoplasms was fenestrated. Hypertrophy and hyperplasia of endothelial cells were observed only in the small lesions. The proliferated and enlarge endothelial cells often partially occluded the vascular lumen and formed multichannel vascular lumina. Many fenestrae of capillaries were found in small neoplasms, but these were rarely identified in the large extracanalicular lesions. The gap junctions of endothelium in small nerve-sheath neoplasms were long, wavy, and convoluted, had no openings, and differed from those of large lesions in which the tight junctions were short, straight, and occasionally patent. Additionally, heavy vascularization and erythrocytes within basement membranes were observed only in large neurilemmomas. These ultrastructural features may constitute a basis for differences between large and small acoustic neurilemmomas noted in cerebrospinal fluid findings.

[The anterior inferior cerebellar artery. Anatomy, clinical aspects and microneurosurgery]

The anterior inferior cerebellar artery (Aica) is the principal vessel of the cerebellopontine angle. It consistently originates from the caudal third of the basilar artery, proceeds to the internal auditory meatus, coming in close proximity to the facial and vestibulocochlear nerves, and then arches along the neighboring subsurface of the cerebellum. Four sections of the artery are distinguished on the basis of the topography and branching pattern. The Aica supplies the pontomedullar junction laterally, the inner ear through the labyrinthine artery and portions of the cerebellar cortex below the horizontal cerebellar fissure. It may contribute to the supply of the petrosal dura, the choroid plexus in the lateral recess of the fourth ventricle and the middle cerebellar peduncle. Its labyrinthine and subarcuate branches firmly anchor the vessel to the petrous bone. This explains why angiograms in cerebellopontine angle processes typically show displacement patterns. Angiographically the Aica is best visualized in the a.p. view. On lateral films useful information is unlikely without subtraction techniques or angiotomography. Symptoms caused by Aica-lesions or occlusions have primarily been explained in terms of reduced blood supply in the brainstem and inner ear, as perfusion in the cerebellar region supplied by the vessel can be adequately maintained by arterio-arterial anastomoses of the other cerebellar arteries. As a rule, the Aica is not prominently involved in the supply of acoustic neurinomas, since these tumors are epiarachnoidal and, as a result, predominantly supplied by dural vessels. This explains why Aica can be preserved even if a radical approach is used for extirpating acoustic neurinomas.

Blood supply of acoustic neurinomas

The arterial blood supply of acoustic neurinomas is reviewed on the basis of normal and pathological anatomical findings as well as neuroradiological and intra-operative observations. Available data suggest that, as a rule, the tumour primarily receives blood from the external carotid by way of dural vessels, with the occipital artery playing a prominent role. The cerebellar vessels, including the anterior inferior cerebellar artery, are apparently no more than secondary contributors. In the light of these observations, selective external carotid angiography on the diseased side is recommended in acoustic neurinomas. In hypervascularized neurinomas preoperative embolization of afferent external carotid branches is discussed as a potential supplementary procedure.

Microsurgical relationships of the anterior inferior cerebellar artery and the facial-vestibulocochlear nerve complex

The relationship of the anterior inferior cerebellar artery (AICA) to the facial (7th) and vestibulocochlear (8th) nerves was studied using 3x to 20x magnification in 50 cerebellopontine angles (CPAs) from 25 adult cadavers. The AICA originated from the basilar artery as a single (72% of the CPAs), duplicate (26%), or triplicate (2%) artery. Each of the 50 CPAs had one or more arterial trunks that coursed in close proximity to the 7th and 8th cranial nerves and thus were said to be nerve-related. The nerve-related arterial trunks were divided into three segments based on their relationship to the nerves and meatus: the premeatal, meatal, and postmeatal segments. The meatal segment projected to the meatus or into the canal in 64% of the CPAs. In relation to the nerves, the premeatal segment was most commonly anteroinferior, the meatal segment was inferior, and the postmeatal segment was posteroinferior. The nerve-related branches of the AICA gave rise to internal auditory arteries in 100% of the 50 CPAs, recurrent perforating arteries in 82%, and the subarcuate artery in 72%. The internal auditory and recurrent perforating arteries arose most commonly from the premeatal segment, and the subarcuate artery arose most commonly from the postmeatal segment. There were one to four internal auditory arteries per CPA, zero to three recurrent perforating arteries, and zero or one subarcuate artery. The effects of occlusion of the nerve-related arteries and their involvement in conditions treated by neurosurgeons are reviewed.

Angiographic diagnosis of acoustic neurinomas and meningiomas in the cerebellopontine angle--a reappraisal

Forty-two acoustic neurinomas and seven meningiomas in the cerebellopontine angle were reviewed, and the radiological differential diagnosis of these tumors is discussed. Though enlarged internal auditory meati and characteristic CT findings were reasonably reliable indicators for the diagnosis of acoustic neurinomas, it was angiography which substantiated their correct diagnosis. An arcuate vein was frequently demonstrated with acoustic neurinomas, but never with meningiomas. Visualization of tangled veins seems to favor a diagnosis of acoustic neurinomas. Contrary to earlier reports, tumor stains were most frequently visualized using selective external carotid arteriography. The degree of tumor stains did not aid in differentiating acoustic neurinomas from meningiomas. The importance of using angiotomography, especially in the anteroposterior projection, and external carotid angiography during prolonged injections of large amounts of contrast media, is emphasized.

Acoustic neurilemmoma. Clinicoanatomical study of 103 patients

✓ Clinical data in 103 patients with acoustic neurilemmoma were correlated with anatomical findings. The tumors were more common in women. Peak prevalence was in the fifth and sixth decade without difference between the sexes. The neoplasms were divided into four sizes: small, medium, large, and giant. Small (intracanalicular) tumors occurred more often in men, were of equal frequency in the decades from 20 to 70 years, were generally associated with long duration of illness, were highly cellular, and had few blood vessels. They, therefore, differed from extracanalicular neurilemmomas, and are better considered as “minimal” rather than “early” tumors. Large and giant lesions occurred more often in women, were more heavily vascularized and collagenized, were more liable to bleed, contained fewer cells, and were often associated with symptoms of short duration. The length of illness ranged from 1 month with a 6-cm lesion, to 30 years with a 1-cm mass. It is suggested that although most tumors enlarge slowly, the rate of growth may vary widely. The unilateral acoustic neurilemmoma that rarely occurs in the first two decades of life may be a limited form of von Reckinghausen's disease. Mortality in this series was nil, and hence was unrelated to size of tumor as described in earlier reports. Angiomas were found in 24 schwannomas, and microscopic calcification in four. Vascular spaces resembling cysts often were formed by tumor cells. The histological development of acoustic neurilemmoma is hypothetically reconstructed.

Light and electron microscopic observations of blood vessels in neurilemoma

A study of 105 cases of neurilemoma disclosed frequent alterations of blood vessels, including hyalinized walls. Many vascular walls were formed by tumor cells. Two cases were analyzed by electron microscopy, and showed fenestrae, patent interendothelial gap junctions, and leakage of RBCs. The presence of erythrocytes in the gap junction and outside vessels is a factor acounting for xanthochromia of the CSF, and serum leakage for the frequent increase in CSF protein in cases of neurilemoma. Attenuation of endothelial cells increases the liability of vessels to bleed within the tumor. Massive bleeding may cause subarachnoid hemorrhage on rare occasions. Hyalinized vessels and dense collagen are features contributing to the relative infrequence of major hemorrhage. Evidence is presented that Schwann and perineural cells are similar.

[Microtopography of cerebellopontine angle structures in acoustic neuroma]

The structures of the cerebellopontine angle in neurinoma of the auditory nerve were studied in autopsy material and during surgical intervention with the use of an operative microscope. Principally different variants of the relationships between the cerebellopontine angle structures and the neurinoma capsule in intra- and extracisternal localization of the tumor were revealed. The greatest difficulties occur in exposure of the capsule of an intracisternal neurinoma which is tightly connected with the structures of the cerebellopontine angle by means of strong connective-tissue trabeculae. In extracisternal localization of the tumor its capsule is easily separated from the arachnoid, which is pushed to the brain stem, because there are no trabeculae between these structures. The main source of blood supply to the tumor irrespective of its localization is the anterior inferior cerebellar artery.

Cerebellopontine angle tumor: diagnosis by oblique projection vertebral angiography

Oblique projection vertebral angiography is the simplest and most accurate angiographic method of detecting small cerebellopontine angle tumors. The vascular blood supply to the tumor and brainstem is displayed as the surgeon will encounter it during lateral suboccipital craniotomy. The procedure is comfortable for the patient, technically easy to perform, and reproducible. Interpretation is relatively unaffected by variations in vascular anatomy or superimposed vessel or bone images. This method can be used to supplement routine views, or be performed alone with stereoscopic filming.