A watch, wait, and rescan approach for incidental benign-appearing notochordal lesions of the skull base.

OBJECTIVE: The aim of this study was to describe the natural history of incidental benign-appearing notochordal lesions of the skull base with specific attention to features that can make differentiation from low-grade chordoma more difficult, namely contrast uptake and bone erosion. METHODS: In this retrospective case series, the authors describe the clinical outcomes of 58 patients with incidental benign-appearing notochordal lesions of the clivus, including those with minor radiological features of bone erosion or contrast uptake. RESULTS: All lesions remained stable during a median follow-up of almost 3 years. Thirty-seven (64%) patients underwent contrast-enhanced MRI; lesions in 14 (38%) of these patients exhibited minimal contrast enhancement. Twenty-seven (47%) patients underwent CT; lesions in 6 (22%) of these patients exhibited minimal bone erosion. CONCLUSIONS: These data make the case for monitoring selected cases of benign-appearing notochordal lesions of the clivus in the first instance even when there is minor contrast uptake or minimal bone erosion.

Radiation treatment of benign tumors in NF2-related-schwannomatosis: A national study of 266 irradiated patients showing a significant increase in malignancy/malignant progression.

Background: Radiation treatment of benign tumors in tumor predisposition syndromes is controversial, but short-term studies from treatment centers suggest safety despite apparent radiation-associated malignancy being reported. We determined whether radiation treatment in NF2-related schwannomatosis patients is associated with increased rates of subsequent malignancy (M)/malignant progression (MP). Methods: All UK patients with NF2 were eligible if they had a clinical/molecular diagnosis. Cases were NF2 patients treated with radiation for benign tumors. Controls were matched for treatment location with surgical/medical treatments based on age and year of treatment. Prospective data collection began in 1990 with addition of retrospective cases in 1969. Kaplan-Meier analysis was performed for malignancy incidence and survival. Outcomes were central nervous system (CNS) M/MP (2cm annualized diameter growth) and survival from index tumor treatment. Results: In total, 1345 NF2 patients, 266 (133-Male) underwent radiation treatments between 1969 and 2021 with median first radiotherapy age of 32.9 (IQR = 22.4-46.0). Nine subsequent CNS malignancies/MPs were identified in cases with only 4 in 1079 untreated (P < .001). Lifetime and 20-year CNS M/MP was ~6% in all irradiated patients-(4.9% for vestibular schwannomas [VS] radiotherapy) versus <1% in the non-irradiated population (P < .001/.01). Controls were well matched for age at NF2 diagnosis and treatment (Males = 133%-50%) and had no M/MP in the CNS post-index tumor treatment (P = .0016). Thirty-year survival from index tumor treatment was 45.62% (95% CI = 34.0-56.5) for cases and 66.4% (57.3-74.0) for controls (P = .02), but was nonsignificantly worse for VS radiotherapy. Conclusion: NF2 patients should not be offered radiotherapy as first-line treatment of benign tumors and should be given a frank discussion of the potential 5% excess absolute risk of M/MP.

Intraoperative diagnosis of facial schwannomas: a multicenter summation of clinical experience, preoperative avoidance, and intraoperative management protocol.

OBJECTIVE: Preoperative differentiation of facial nerve schwannoma (FNS) from vestibular schwannoma (VS) can be challenging, and failure to differentiate between these two pathologies can result in potentially avoidable facial nerve injury. This study presents the combined experience of two high-volume centers in the management of intraoperatively diagnosed FNSs. The authors highlight clinical and imaging features that can distinguish FNS from VS and provide an algorithm to help manage intraoperatively diagnosed FNS. METHODS: Operative records of 1484 presumed sporadic VS resections between January 2012 and December 2021 were reviewed, and patients with intraoperatively diagnosed FNSs were identified. Clinical data and preoperative imaging were retrospectively reviewed for features suggestive of FNS, and factors associated with good postoperative facial nerve function (House-Brackmann [HB] grade ≤ 2) were identified. A preoperative imaging protocol for suspected VS and recommendations for surgical decision-making following an intraoperative FNS diagnosis were created. RESULTS: Nineteen patients (1.3%) with FNSs were identified. All patients had normal facial motor function preoperatively. In 12 patients (63%), preoperative imaging demonstrated no features suggestive of FNS, with the remainder showing subtle enhancement of the geniculate/labyrinthine facial segment, widening/erosion of the fallopian canal, or multiple tumor nodules in retrospect. Eleven (57.9%) of the 19 patients underwent a retrosigmoid craniotomy, and in the remaining patients, a translabyrinthine (n = 6) or transotic (n = 2) approach was used. Following FNS diagnosis, 6 (32%) of the tumors underwent gross-total resection (GTR) and cable nerve grafting, 6 (32%) underwent subtotal resection (STR) and bony decompression of the meatal facial nerve segment, and 7 (36%) underwent bony decompression only. All patients undergoing subtotal debulking or bony decompression exhibited normal postoperative facial function (HB grade I). At the last clinical follow-up, patients who underwent GTR with a facial nerve graft had HB grade III (3 of 6 patients) or IV facial function. Tumor recurrence/regrowth occurred in 3 patients (16%), all of whom had been treated with either bony decompression or STR. CONCLUSIONS: Intraoperative diagnosis of an FNS during a presumed VS resection is rare, but its incidence can be reduced further by maintaining a high index of suspicion and undertaking further imaging in patients with atypical clinical or imaging features. If an intraoperative diagnosis does occur, conservative surgical management with bony decompression of the facial nerve only is recommended, unless there is significant mass effect on surrounding structures.

Prevalence and natural history of schwannomas in neurofibromatosis type 2 (NF2): the influence of pathogenic variants.

This study explores the natural history of vestibular, trigeminal and lower cranial nerve schwannomas (VS, TS, LCNS) in patients with Neurofibromatosis type 2 (NF2), to understand how pathogenic variants (PVs) of the NF2 gene affect tumour burden and growth rate, via a retrospective analysis of a UK NF2 centre database and imaging. VS, TS and LCNS location and size were measured in accordance with a standardised protocol. PVs were categorised in accordance with the UK NF2 Genetic Severity Score (GSS). 153 patients (age 5-82) had 458 schwannomas, of which 362 were previously untreated comprising: 204 VS, 93 TS, and 65 LCNS (IX, X, XI). 322 schwannomas had sequential imaging allowing growth rate analysis with a mean follow-up of 45 months. VS were universally present, and bilateral in 146/153 cases. 65% of tumours grew >2 mm during the study period at mean rate 2.0 mm/year. Significant association was found between increasing GSS and growth rate. TS occurred in 66/153 patients (bilateral in 27/153); 31% of tumours showed growth (mean 1.8 mm/yr). Significant increase in tumour prevalence was noted with increasing GSS. LCNS were found in 47/153 patients (bilateral in 19/153); 27% of tumours showed growth (mean 1.9 mm/yr). The trend for increased prevalence with increasing GSS did not reach significance. VS growth rate was significantly influenced by GSS and they were much more likely to grow than TS and LCNS. TS prevalence also correlated with increasing GSS.

Disease course of neurofibromatosis type 2: a 30-year follow-up study of 353 patients seen at a single institution.

BACKGROUND: Limited data exist on the disease course of neurofibromatosis type 2 (NF2) to guide clinical trial design. METHODS: A prospective database of patients meeting NF2 diagnostic criteria, reviewed between 1990 and 2020, was evaluated. Follow-up to first vestibular schwannoma (VS) intervention and death was assessed by univariate analysis and stratified by age at onset, era referred, and inheritance type. Interventions for NF2-related tumors were assessed. Cox regression was performed to determine the relationship between individual factors from time of diagnosis to NF2-related death. RESULTS: Three hundred and fifty-three patients were evaluated. During 4643.1 follow-up years from diagnosis to censoring, 60 patients (17.0%) died. The annual mean number of patients undergoing VS surgery or radiotherapy declined, from 4.66 and 1.65, respectively, per 100 NF2 patients in 1990-1999 to 2.11 and 1.01 in 2010-2020, as the number receiving bevacizumab increased (2.51 per 100 NF2 patients in 2010-2020). Five patients stopped bevacizumab to remove growing meningioma or spinal schwannoma. 153/353 (43.3%) had at least one neurosurgical intervention/radiation treatment within 5 years of diagnosis. Patients asymptomatic at diagnosis had longer time to intervention and better survival compared to those presenting with symptoms. Those symptomatically presenting <16 and >40 years had poorer overall survival than those presenting at 26-39 years (P = .03 and P = .02, respectively) but those presenting between 16 and 39 had shorter time to VS intervention. Individuals with de novo constitutional variants had worse survival than those with de novo mosaic or inherited disease (P = .004). CONCLUSION: Understanding disease course improves prognostication, allowing for better-informed decisions about care.

Incidence of mosaicism in 1055 de novo NF2 cases: much higher than previous estimates with high utility of next-generation sequencing.

PURPOSE: To evaluate the incidence of mosaicism in de novo neurofibromatosis 2 (NF2). METHODS: Patients fulfilling NF2 criteria, but with no known affected family member from a previous generation (n = 1055), were tested for NF2 variants in lymphocyte DNA and where available tumor DNA. The proportion of individuals with a proven or presumed mosaic NF2 variant was assessed and allele frequencies of identified variants evaluated using next-generation sequencing. RESULTS: The rate of proven/presumed mosaicism was 232/1055 (22.0%). However, nonmosaic heterozygous pathogenic variants were only identified in 387/1055 (36.7%). When variant detection rates in second generation nonmosaics were applied to de novo cases, we assessed the overall probable mosaicism rate to be 59.7%. This rate differed by age from 21.7% in those presenting with bilateral vestibular schwannoma <20 years to 80.7% in those aged ≥60 years. A mosaic variant was detected in all parents of affected children with a single-nucleotide pathogenic NF2 variant. CONCLUSION: This study has identified a very high probable mosaicism rate in de novo NF2, probably making NF2 the condition with the highest expressed rate of mosaicism in de novo dominant disease that is nonlethal in heterozygote form. Risks to offspring are small and probably correlate with variant allele frequency detected in blood.

Identifying the deficiencies of current diagnostic criteria for neurofibromatosis 2 using databases of 2777 individuals with molecular testing.

PURPOSE: We have evaluated deficiencies in existing diagnostic criteria for neurofibromatosis 2 (NF2). METHODS: Two large databases of individuals fulfilling NF2 criteria (n = 1361) and those tested for NF2 variants with criteria short of diagnosis (n = 1416) were interrogated. We assessed the proportions meeting each diagnostic criterion with constitutional or mosaic NF2 variants and the positive predictive value (PPV) with regard to definite diagnosis. RESULTS: There was no evidence for usefulness of old criteria "glioma" or "neurofibroma." "Ependymoma" had 100% PPV and high levels of confirmed NF2 diagnosis (67.7%). Those with bilateral vestibular schwannoma (VS) alone aged ≥60 years had the lowest confirmation rate (6.6%) and reduced PPV (80%). Siblings as a first-degree relative, without an affected parent, had 0% PPV. All three individuals with unilateral VS and an affected sibling were proven not to have NF2. The biggest overlap was with LZTR1-associated schwannomatosis. In this category, seven individuals with unilateral VS plus ≥2 nondermal schwannomas reduced PPV to 67%. CONCLUSIONS: The present study confirms important deficiencies in NF2 diagnostic criteria. The term "glioma" should be dropped and replaced by "ependymoma." Similarly "neurofibroma" should be removed. Dropping "sibling" from first-degree relatives should be considered and testing of LZTR1 should be recommended for unilateral VS.

Familial unilateral vestibular schwannoma is rarely caused by inherited variants in the NF2 gene.

OBJECTIVES/HYPOTHESIS: Unilateral vestibular schwannoma (VS) occurs with a lifetime risk of around 1 in 1,000 and is due to inactivation of the NF2 gene, either somatically or from a constitutional mutation. It has been postulated that familial occurrence of unilateral VS occurs more frequently than by chance, but no causal mechanism has been confirmed. STUDY DESIGN: Retrospective database analysis. METHODS: The likelihood of chance occurrence of unilateral VS, or occurring in the context of neurofibromatosis type 2 (NF2), was assessed using national UK audit data and data from the national NF2 database. Families with familial unilateral VS (occurrence in first- and second-degree relatives) were assessed for constitutional NF2 and LZTR1 genetic variants, and where possible the tumor was also analyzed. RESULTS: Approximately 1,000 cases of unilateral VS occurred annually in the United Kingdom between 2013 and 2016. Of these, 2.5 may be expected to have a first-degree relative who had previously developed a unilateral VS. The likelihood of this occurring in NF2 was considered to be as low as 0.05 annually. None of 28 families with familial unilateral VS had a constitutional NF2 intragenic variant, and in nine cases where the VS was analyzed, both mutational events in NF2 were identified and excluded from the germline. Only three variants of uncertain significance were found in LZTR1. CONCLUSIONS: Familial occurrence of unilateral VS is very unlikely to be due to a constitutional NF2 or definitely pathogenic LZTR1 variant. The occurrence of unilateral VS in two or more first-degree relatives is likely due to chance. This phenomenon may well increase in clinical practice with increasing use of cranial magnetic resonance imaging in older patients. LEVEL OF EVIDENCE: 2b Laryngoscope, 129:967-973, 2019.

Schwannomatosis: a genetic and epidemiological study.

OBJECTIVES: Schwannomatosis is a dominantly inherited condition predisposing to schwannomas of mainly spinal and peripheral nerves with some diagnostic overlap with neurofibromatosis-2 (NF2), but the underlying epidemiology is poorly understood. We present the birth incidence and prevalence allowing for overlap with NF2. METHODS: Schwannomatosis and NF2 cases were ascertained from the Manchester region of England (population=4.8 million) and from across the UK. Point prevalence and birth incidence were calculated from regional birth statistics. Genetic analysis was also performed on NF2, LZTR1 and SMARCB1 on blood and tumour DNA samples when available. RESULTS: Regional prevalence for schwannomatosis and NF2 were 1 in 126 315 and 50 500, respectively, with calculated birth incidences of 1 in 68 956 and 1 in 27 956. Mosaic NF2 causes a substantial overlap with schwannomatosis resulting in the misdiagnosis of at least 9% of schwannomatosis cases. LZTR1-associated schwannomatosis also causes a small number of cases that are misdiagnosed with NF2 (1%-2%), due to the occurrence of a unilateral vestibular schwannoma. Patients with schwannomatosis had lower numbers of non-vestibular cranial schwannomas, but more peripheral and spinal nerve schwannomas with pain as a predominant presenting symptom. Life expectancy was significantly better in schwannomatosis (mean age at death 76.9) compared with NF2 (mean age at death 66.2; p=0.004). CONCLUSIONS: Within the highly ascertained North-West England population, schwannomatosis has less than half the birth incidence and prevalence of NF2.

High-Grade Glioma is not a Feature of Neurofibromatosis Type 2 in the Unirradiated Patient.

BACKGROUND: The Manchester criteria for neurofibromatosis type 2 (NF2) include a range of tumors, and gliomas were incorporated in the original description. The gliomas are now widely accepted to be predominantly spinal cord ependymomas. OBJECTIVE: To determine whether these gliomas include any cases of malignant glioma (WHO grade III and IV) through a database review. METHODS: The prospective database consists of 1253 patients with NF2. 1009 are known to be alive at last follow-up. RESULTS: There was a single case of glioblastoma multiforme (GBM; World Health Organization grade IV) in the series and no WHO grade III gliomas. The GBM was in a patient who had previously undergone stereotactic radiosurgery for a vestibular schwannoma. CONCLUSION: High-grade gliomas are not a feature of NF2 in the unirradiated patient and should be excluded from the diagnostic criteria.

Malignant Peripheral Nerve Sheath Tumors are not a Feature of Neurofibromatosis Type 2 in the Unirradiated Patient.

BACKGROUND: The published literature suggests that malignant peripheral nerve sheath tumors (MPNST) occur at increased frequency in neurofibromatosis type 2 (NF2). A recent review based on incidence data in North America showed that 1 per 1000 cerebellopontine angle nerve sheath tumors were malignant. OBJECTIVE: To determine whether MPNST occurred spontaneously in NF2 by reviewing our NF2 database. METHODS: The prospective database consists of 1253 patients with NF2. One thousand and nine are known to be alive at last follow-up. The presence and laterality/pathology of vestibular schwannoma at diagnosis and last follow-up was sought. RESULTS: There were no cases of spontaneous MPNST with 2114 proven (n = 1150) and presumed benign (n = 964) vestibular schwannomas found. Two patients had developed MPNST (1 presumed) after having previously undergone stereotactic radiosurgery for a vestibular schwannoma. CONCLUSION: In this series, and from the literature, malignant transformation of a vestibular schwannoma was not a feature of NF2 in the unirradiated patient. NF2 patients should not be told that they have an increased risk of malignant change in a vestibular schwannoma unless they undergo radiation treatment. However, very much larger datasets are required before it can be determined whether there is any association between NF2 and MPNST in the unirradiated patient.

Calcifying pseudoneoplasm of the neuraxis (CaPNoN): an unusual cause of third nerve palsy in a teenager.

An 18-year-old part-time teacher presented with headache and diplopia. Physical examination showed partial left oculomotor palsy. Neurology examination was otherwise unremarkable. Cross-sectional imaging was arranged for investigation of third nerve palsy. On CT scan, the lesion was calcified, and on MRI, hypointense on T 1 and T 2 weightedimages with thin rim enhancement, resembling an atypical meningioma. CT angiogram showed no vascular connection. Following worsening diplopia and a slight increase in lesion size on follow-up MRI, the patient was re-reviewed in our regional skull base multidisciplinary team meeting, where a decision for excision was made. Pre-operatively, the absence of a vascular connection was confirmed on catheter angiogram. Histopathological examination demonstrated features typical of calcified pseudoneoplasm of the neuraxis, with extensive metaplastic calcification with stroma containing variable fibrovascular tissue and focal inflammatory cell infiltrates, spindle and epithelioid cells, and psammoma bodies at the rim of the lesion. Following surgery, the patient had persisting diplopia. He remains under clinical review. As surgical resection is considered curative, no further imaging follow-up is planned.

Bisphosphonate-induced osteonecrosis of the maxilla presenting as a cicatricial ectropion.

CASE REPORT: A 63-year-old gentleman, who was being treated with bisphosphonates for multiple myeloma, presented with a cicatricial ectropion of the lower eyelid, without exposure keratopathy. A CT scan demonstrated extensive destruction of bone with an infraorbital fracture surrounded by sclerotic bony changes. The patient was managed conservatively with discontinuation of bisphosphonate therapy and topical ocular lubricants. The patient's condition remained unchanged a year after this initial management.

Osteoradionecrosis of the exenterated orbit.

Osteoradionecrosis (ORN) occurs in an estimated 2% of head and neck-irradiated patients. It is seen most commonly in the mandible with other reported sites including the maxilla, temporal bone, clavicle, and vertebrae. It is defined as an area of exposed devitalised irradiated bone, with failure to heal during a period of at least 3 months, in the absence of local neoplastic disease. We report 2 cases of ORN following postoperative radiotherapy given to patients who had undergone an orbital exenteration. ORN can develop spontaneously in one-third of cases, although in the majority of patients, it is induced by secondary trauma. Radiotherapy induces an endarteritis in the small blood vessels of bone, thus favouring the generation of small thrombi that obliterate the vascular lumen and interrupt tissue perfusion. Likewise, irradiation impairs the function of osteoblasts, manifesting as osteopenia, with impairment of the repair and remodelling capacity of bone. Prior radiation exposure can thus decrease bone vascularity and injure its reserve reparative capacity. It is important to differentiate ORN from local recurrence of malignancy, bone metastasis, radiation-induced sarcoma, and infection. CT and MRI are effective diagnostic tools. Clinical management of ORN is complex and unsatisfactory. Treatment remains difficult, and prevention is paramount. A history of radiotherapy should alert clinicians to detect bone exposure or excessively prolonged socket healing. Early diagnosis with a high index of suspicion can achieve higher control rates with conservative management. Our case series reports a rare, previously unreported, but important complication of radiation therapy of the exenterated orbit.

Isolated Pupil-Involving Third Nerve Palsy as the First Presentation of Sarcoidosis.

Neurosarcoidosis is seen in 5-15% of patients with systemic sarcoidosis. The most common cranial nerve presentations are optic neuropathy and facial nerve palsy. The authors present a case of sarcoidosis presenting with a pupil-involving third nerve palsy. The patient responded to corticosteroid therapy with resolution of investigations her cranial nerve palsy but progressed to develop cerebellar signs. This is the first documented case of a pupil-involving third nerve palsy occurring as the first presentation of neurosarcoidosis. Although typically a pupil-involving third nerve palsy necessitates urgent neuroimaging to rule out a posterior communicating artery aneurysm, it is important to recognise inflammatory causes in the differential diagnosis.

A case of a spontaneous intraorbital arteriovenous fistula: clinico-radiological findings and treatment by transvenous embolisation via the superior ophthalmic vein.

A 72-year-old male presented with progressive right axial proptosis and red eye. Catheter angiography demonstrated an intraorbital arteriovenous fistula (IAVF) distal to the central retinal artery (CRA). Transvenous embolisation following direct surgical exposure of the superior ophthalmic vein (SOV) resulted in rapid resolution of his symptoms and signs. Transvenous embolisation via the SOV is a safe, effective alternative to transarterial embolisation for treating spontaneous IAVF where transarterial embolisation poses a risk of CRA occlusion.

Rate and clinical impact of intra-procedural complications during coil embolisation of ruptured small (3 mm or less) cerebral aneurysms.

OBJECTIVE: Coiling of small (≤3 mm) cerebral aneurysms can be technically challenging and is associated with increased procedural-related morbidity and mortality. The authors report the clinical and radiological results following coiling of ruptured small cerebral aneurysms in a single-institution, and define the rates of intra-procedural rupture and thromboembolism. METHODS: A retrospective analysis was conducted on consecutive patients from 01/01/2008 to 31/12/2010 with subarachnoid haemorrhage (SAH) from ruptured cerebral aneurysms (≤3 mm) managed in a tertiary neurosurgical institution in the United Kingdom. RESULTS: Of the 108 patients identified, 72 patients (66.7%) underwent coil embolisation. A favourable outcome, defined as a Glasgow outcome score of 4-5, was achieved in 63 (87.5%) of these patients. Intra-procedural complications were observed in 11.1% (±7.3% 95% CI) of cases, wherein the rate of intra-procedural rupture was determined to be 8.3% (±6.4% 95% CI) and intra-procedural thromboembolism to be 2.8% (±3.8% 95% CI). CONCLUSION: Although coil embolisation of small ruptured cerebral aneurysms is technically feasible and an efficacious means of treatment, it is associated with an increased rate of intra-procedural complications. This should be taken into account when embarking upon treatment of patients with ruptured small cerebral aneurysms.

Double origin of the posterior inferior cerebellar artery with findings on conventional and CT angiography.

A case of double origin of the posterior inferior cerebellar artery (PICA) is presented, with appearances on both cross-sectional imaging and conventional angiography. An associated aneurysm was found, strengthening the belief that this variation is associated with intracranial aneurysms. Furthermore, this is the first report of a right-sided double-origin PICA in a female patient, which calls into question the previously proposed male and left-sided preponderance of this variation.

Coincident Giant Cavernous Angioma and Large Middle Cerebral Artery Aneurysm.

Cavernous angiomas although relatively common lesions rarely reach a large size. They have a well documented association with AVMs, capillary telangiectases and venous angiomas but are not specifically associated with intracerebral aneurysms. We present a case of what we believe to be the 4th largest reported giant cavernous angioma to present in adulthood. This cavernous angioma also happened to be associated with a large intracerebral aneurysm, an association not previously reported. The sometimes confusing nomenclature of cavernous angiomas and other similar vascular malformations is also discussed.

Visual pathway compromise after hydrocoil treatment of large ophthalmic aneurysms.

OBJECTIVE: Hydrogel-coated coils (MicroVention, Inc., Aliso Viejo, CA) for endovascular aneurysm treatment offer the theoretical advantages of increased volumetric occlusion, thrombus stabilization, and improved neointimal healing. Reports of local inflammation and hydrocephalus after coiling of unruptured aneurysms have raised questions about the safety profile or appropriate usage of these new devices. CLINICAL PRESENTATION: Two patients with large ophthalmic aneurysms underwent elective endovascular coiling with HydroCoils. Three to 4 weeks later, they developed profound, progressive bilateral visual loss. Magnetic resonance imaging scans demonstrated extensive enhancement of the coil ball, surrounding brain parenchyma, and optic chiasm, with perianeurysmal edema. INTERVENTION: Dexamethasone produced impressive but temporary improvement in vision in one patient; the other experienced only minor improvement. One patient also developed hydrocephalus; ventriculoperitoneal shunting reduced ventricular size but had no effect on vision. Follow-up imaging demonstrated persistent enhancement of the coil ball, as well as recurrence and extension of the abnormal signal in the parenchyma and along the optic tract. CONCLUSION: Both patients have been left with no functional vision in the eye ipsilateral to the aneurysm and have experienced marked visual field loss and reduced acuity in the contralateral eye. Ongoing international studies will provide more information on the rate of inflammatory complications. The biological mechanisms underlying the phenomenon also require investigation. Meanwhile, we caution against using HydroCoils in situations in which worsened mass effect or local inflammation would have highly deleterious consequences, such as in large aneurysms adjacent to the visual pathways or the brainstem.