Optic Nerves Sheath Meningiomas

Optic Nerve Sheath Meningiomas Clinical Manifestations PATRICK A. SIBONY, MD,* HOWARD R. KRAUSS, MD,* JOHN S. KENNERDELL, MD,*t JOSEPH C. MAROON, MD,t THOMAS L. SLAMOVITS, MD*t

Abstract: A retrospective clinical study of optic nerve sheath meningiomas based on 22 patients showed that symptoms most commonly develop in women between the ages of 35 and 60 years. The most common presenting symptoms were decreased vision and transient visual obscurations. In the earliest stages, many patients presented with normal to mildly impaired acuity (despite subjectively decreased vision), optic disc edema and enlargement of the blind spot. Optic disc edema was frequently associated with refractile bodies indicative of chronic swelling. Optic disc edema preceded the development of optic atrophy. Another group of patients presented with a history of longstanding vision loss, visual acuity of 20/200 or worse and optic atrophy. Optociliary shunt vessels were late findings only seen in five patients. The most consistent visual field abnormality was peripheral constriction. Cecocentral scotomas were uncommon. Intracranial involvement was present in five patients. There were two patients with bilateral optic nerve sheath meningiomas without CT evidence of intracranial involvement. Computerized tomography was found to be indispensible in the diagnosis of optic nerve sheath meningiomas and the detection of intracranial involvement. [Key words: drusen, optic atrophy, optic disc edema, optic nerve sheath meningioma, optic nerve tumor, optic neuropathy, orbital tumor, perioptic meningioma, transient monocular blindness, transient visual obscurations.] Ophthalmology 91:1313-1326, 1984 .

The most characteristic clinical manifestation of optic nerve sheath meningiomas is slowly progressive vision loss, a feature that is frequently recognized only after

From the Division of Neuro-ophthalmology, Pittsburgh Eye and Ear Hospital,* the Department of Neurologyt and the Department of Neurosurgery,:j: University of Pittsburgh Medical School, Pittsburgh, Pennsylvania. Presented at the Eighty-eighth Annual Meeting of the American Academy of Ophthalmology, Chicago, Illinois, October 30-November 3, 1983. Dr. Sibony is presently in the Division of Ophthalmology, Department of Neurology, SUNY-Stony Brook, Stony Brook, NY; Dr Krauss is presently in the Department of Ophthalmology, University of Texas Medical School, Dallas, Texas. Reprint requests toP. A. Sibony, MD, Dept. of Neurology, HSC, SUNY Stony Brook, Stony Brook, NY 11794.

months or years of followup. t-s Likewise, the syndrome of longstanding vision loss, optociliary shunt vessels and optic atrophy in a middle aged woman, is a late but distinctive feature of spheno-orbital meningioma. 7•9- 12 In the past, delay in the diagnosis of optic nerve sheath meningioma was, in part, a consequence of the risks and limitations of older neuroradiographic techniques. The early clinical manifestations of optic nerve sheath meningiomas have therefore not received as much att~ntion as those late features noted above. The advent of high resolution computerized tomography (CT), however, has made early diagnosis possible. The purpose of this communication is to characterize the clinical presentation and course of optic nerve sheath meningiomas based on our series of twenty-two patients. Early clinical features will be emphasized. We will not address the controversial issues of treatment 1- 5 in this report. 1313

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Table 1. Clinical Manifestations of 22 Optic Patient No.

Age (Years)

Sex

Laterality

Presenting Symptoms

Duration

Visual Acuity

40

F

OD

1 month

20/15

2

49

F

OS

44

F

OD

2 years 1 year 6 months

20/20

3

Transient visual obscurations on elevation; Headaches Decreased vision Proptosis Decreased vision

20/25

4

46

F

OS

Decreased vision

3 months

20/25

5

43

F

OS

36

M

OD

7

44

M

OD

1 year 7 months 1 year 7 months 8 months

20/20

6

Decreased vision Transient visual obscurations. Headache Transient visual obscurations. Decreased vision

8 9

59 57

F M

OD OS

18 months

20/20 20/30

10 11

42 43

M M

OD OD

36

F

OD

3 years 18 months 9 years

20/25 20/40

12 13 14 15

35 45 41

F M F

OD OD OS

16 17

39 48

F F

OS OS

Decreased vision Decreased vision Transient visual obscurations Proptosis Decreased vision Exotropia Decreased vision Headache Blindness on abduction Decreased vision Decreased vision Decreased vision Transient visual obscurations Decreased vision Asymptomatic

18 19 20

35 24 66

F F M

OD OD OS

Decreased vision Esotropia Decreased vision

21

18

F

22

48

F

OD OS OD OS

Decreased Decreased Decreased Decreased

vision vision vision vision

20/20 20/30

20/50 1 month 1 year 2 years 1 year 6 months 9 years 3 years 1 month 15 years

6 years 7 years

20/60 HM CF LP CF 20/200 HM LP HM 20/70 20/70 HM

M = male; F = female; OD = right eye; OS = left eye; CT = computerized tomography; HM = hand motion; CF = count fingers; LP = light perception; APD = afferent pupil defect; N = normal; A = abnormal; FNAB = fine needle aspiration biopsy; - = information not available. Group 1: cases #1-13; Group II: cases #14-22.

MATERIALS AND METHODS Between 1975 and 1983, 22 patients were seen at the Pittsburgh Eye and Ear Hospital with a diagnosis of optic nerve sheath meningioma. Sixteen (73%) patients had histologic confirmation of the diagnosis. Tissue was obtained only after the development of progressive and significant visual loss or evidence of intracranial extension. Sjx patients (27%) with presumed optic nerve sheath meningiomas are included. The clinical diagnosis was based on several criteria including age (histology was required if the patient was under 35 years of age); a history of slowly progressive vision loss; evidence of 1314

an optic neuropathy (ie. decreased vision, abnormal visual fields, afferent pupillary defects, color or brightness desaturation, and dyschromatopsia); the presence of optic atrophy or optic disc edema; and a CT scan demonstrating optic nerve enlargement. All patients underwent a complete medical and neuro-ophthalmological evaluation. Viuscal fields were performed on a Haag-Streit Goldmann perimeter. Stereoscopic photographs were used to analyze the optic discs and fundi. The medical evaluation was directed at ruling out sarcoidosis, syphilis, collagen vascular disease and lymphoproliferative disorders. All patients underwent computerized tomography of the head and orbit. In selected cases optic canal tomograms, transfemoral arteriography, or orbital ultrasonography were performed.

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Nerve Sheath Meningiomas at Presentation Visual Fields

Pupil

Color

Proptosis

CT SCAN

Diagnosis

Fusiform

Biopsied

Globular

Clinical

Enlarged blind spot

N

N

Enlarged blind spot

APD

N

Enlarged blind spot with peripheral constriction Enlarged blind spot with inferonasal step Enlarged blind spot

APD

A

Tubular

Biopsied

APD

A

Tubular

Biopsied

APD

N

Tubular

Clinical

Enlarged blind spot

APD

Tubular

Clinical

Enlarged blind spot with inferonasal step Enlarged blind spot Enlarged blind spot

APD

A

3 mm

Tubular

Biopsied

APD N

A N

2 mm 3 mm

Fusiform Tubular

Biopsied Biopsied

Enlarged blind spot Enlarged blind spot with peripheral constriction Monocular temporal hemianopsia

N APD

N N

6 mm 3 mm

Globular Fusiform

Biopsied Clinical

APD

A

3 mm

Globular

Biopsied

Centrocecal scotoma Temporal islands Temporal islands

APD APD APD

A A A

4 mm 2 mm 2 mm

Fusiform Tubular Tubular

Biopsied Clinical Biopsied

Tempora/nasal islands Altitudinal inferonasal step Peripheral constriction Temporal islands Not performed

APD APD

A

2 mm 2.5 mm

Tubular Globular

FNAB Biopsied

APD APD APD

A

2 mm

Tubular Fusiform Globular

Clinical FNAB Biopsied

APD N

A A A A

Tubular Tubular Tubular Tubular

Biopsied

Peripheral constriction Peripheral constriction Centrocecal scotoma Nasal islands

APD

5 mm

2 mm

0

0

marked proptosis

0 0

RESULTS Results are tabulated in Table 1. Twenty-two patients with optic nerve sheath meningiomas were evaluated: 12 (55%) involved the right side, 8 (36%) were on the left, and two patients (9%) had bilateral involvement. Our cohort was arbitrarily divided into two groups based on the degree of visual impairment and disc appearance at presentation. Group I ("early"; cases 113), defined by the presence of optic disc edema and normal to moderately impaired vision, included ten patients (45%) with visual acuities of 20/30 or better and three patients ( 14%) with visual acuties between 20/40 and 20/60. There were nine patients (41%) in

Miscellaneous Periforaminal intracranial extension 2 years after presentation Tuberculum sellae and olfactory groove meningioma noted at presentation.

Neurofibromatosis, Periforaminal intracranial extension 4 years after presentation. Falx meningioma and anterior cerebral artery aneurysm noted 3 years after presentation Periforaminal intracranial meningioma noted at presentation

Biopsied

Group II ("late"; cases 14-22) characterized by profound visual loss (worse than 20/100) and optic atrophy. Age at presentation. The age distribution was 18 to 66 years (median, 43 years). Eighty-two percent of our patients were between the ages of 35 and 59. The two youngest patients, ages 18 and 24, were among those with a biopsy-proven diagnosis. There was no significant age difference between groups I and II. Sex. Fifteen women (68%) and 7 men (32%) were studied. Both patients with bilateral optic nerve sheath meningiomas were women. Presenting symptoms. Seventeen patients (77%) complained of decreased vision. Five (23%) presented with transient visual obscurations (TVO). This was typically an early symptom, which sometimes preceded the onset 1315

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Table 2. Presenting Symptoms of Sheath Meningiomas Symptom

No. Patients (%)

Decreased vision Transient visual obscurations Headaches Proptosis Strabismus Blindness on Abduction Asymptomatic

17 (77) 5 (23) 2 (9) 2 (9) 2 (9) 1 (5) 1 (5)

of subjective vtswn loss. TVOs typically lasted for seconds, and occurred with variable frequency from a few to hundreds of episodes per day. One patient could induce them or increase their frequency by looking up. Occasionally, TVOs occurred with changes in posture. Another patient complained of transient monocular blindness whenever she abducted her eye. Proptosis was a less common complaint (9% ); in one case it was the only presenting symptom. Headaches (9%) and strabismus (9%) were also uncommon. Another patient was unaware that her vision was only counting fingers in the involved eye when optic atrophy was discovered on a routine examination for glasses. The duration of symptoms ranged from one month to four years in all but three patients at presentation. Duration of symptoms

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prior to presentation tended to be shorter in the group I than group II, with some overlap between both groups (Table 2). Visual acuity. The visual acuity at presentation varied from 20/15 to light perception. In ten patients (45%) visual acuity was normal or only mildly impaired (20/30 or better) despite subjective complaints of decreased vision. Three patients (14%) were between 20/ 40 and 20/60. These patients were in group I by definition. Only three patients within the "early" group had visual acuity in the involved eye equal to the uninvolved eye. In the ten remaining patients, the uninvolved eye had a visual acuity better by one or more Snellen lines. There were nine patients (41%) in group II with visual acuities less than 20/100. Pupils. All but three patients had afferent pupil defects. Those patients with normal pupil exams also had visions equal to or better than 20/30, normal color vision, enlargement of the physiological blind spot and optic disc edema. Color vision. Color vision was usually abnormal although six (27%) patients responded correctly to all the Ishihara color plates at the time of presentation. Within this group of patients with normal color vision, visual acuity was no worse than 20/40. Exophthalmos. At least 15 (68%) patients had proptosis, varying from 2 to 6 mm. Where data was available,

3

..,..........~~- :lii=='P-......_...._.......,~~1'-+· 'lii=='P-......~

Fig 1. Schematic summary of the visual field defects, their frequencies at presentation (large numerals, lower right) and patterns of progression (small numerals, over arrow).

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thirteen (59%) patients fell within a range of 2 to 4 mm (mean, 3 mm). Proptosis was associated with palpebral fissure asymmetry, lower lid retraction, ptosis, or mild lid swelling. Visual fields. The most common (7 patients, 32%) presenting visual field defect was enlargement of the physiologic blind spot with normal central fields to the 12e. At the other extreme, five patients (23%) with profound visual loss and optic atrophy displayed single or multiple irregularly shaped residual islands of vision at the time of presentation. Four other patients (5 eyes) demonstrated variable degrees of irregular peripheral constriction with or without enlargement of the blind spot. Three patients presented with an altitudinal inferonasal field depression. Cecocentral scotomas were uncommon, occurring in two patients. Finally, one patient presented with a monocular temporal hempianopsia (to the Be object) and enlargement of the blind spot without intracranial or chiasmal involvement. The field in one patient with light perception vision was not obtainable (Fig 1). Ophthalmoscopic abnormalities (Table 3). At presentation, 13 (59%) patients had optic disc edema and 9

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Table 3. Ophthalmoscopic Abnormalities No. Patients (%)

Ocular Finding Disc edema Refractile Bodies Circumpapillary folds Telangiectatic vessels Cotton wool spots Optic atrophy Venous engorgement Optociliary shunt vessels Choroidal folds Hemorrhages

7/13 8/13 6/13 1/13

13 (59)

9 (41)

19 (86) 5 (23) 3 (14) 0

(41%) had optic atrophy. Those patients with optic atrophy usually had acuities of 20/100 or worse, whereas optic disc edema occurred in patients with acuities between 20/15 and 20/60. Venous engorgement was frequently present in both groups of patients. Among those with optic disc edema, eight patients (36%) demonstrated circumpapillary retinal folds (Figure

Fig 2. Optic disc abnormalities. Top left, optic disc edema with refractile bodies and microvascular congestion. Top right, chronic optic disc edema with milder disc elevation and refracticle bodies. Bottom left, optic disc edema with circumpapillary retinal folds temporally. Horizontal choroidal folds are also present in the posterior pole. Bottom right, optic atrophy with venous engorgement and optociliary shunt vessels temporally.

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Fig 3. Computerized tomography demonstrating posterior fusiform enlargement.

Fig 4. Computerized tomography demonstrating globular perioptic mass with central linear lucency.

2, top and bottom left). Retinal folds were most evident at the vertical and temporal peripapillary poles. Severe optic disc edema was noted in six patients (27%) with intrapapillary microvascular abnormalities consisting of numerous fine radially oriented telangiectatic vessels and microaneurysms (Fig 2, top left). Only one patient had cotton wool spots and there was a conspicuous absence of papillary hemorrhage in our cohort. Seven patients (32%) had intrapapillary, yellow, punctate, refractile bodies. These superficial deposits were usually located on the superotemporal and inferotemporal margins of the disc (Fig 2, top). Chronic optic disc edema was noted at presentation in eight patients (36% ), manifested by refractile bodies, variable degrees of disc elevation and yellowish gliotic discoloration (Fig 2, top and bottom left). Three patients with optic disc edema also had horizontal choroidal folds in the posterior pole (Fig 2, bottom left). Choroidal folds were associated with 3 to 5 mm of proptosis, and CT scan did not show evidence of globe compression. Patients with optic atrophy showed diffuse pallor with blurring of the disc margins (Fig 2, bottom right). The disc was usually flat, although one patient with an anteriorly located mass had residual pale optic disc swelling, peripapillary retina-choroidal swelling and extreme venous congestion. One patient with transient visual obscurations had mild residual edema of a predominantly atrophic disc. Another patient who experienced a rapid and profound decline in vision presented with disproportionately mild temporal pallor. Five patients (23%) with optic atrophy had mild sheathing and irregularities of vessel caliber of the papillary arterioles. Optociliary shunt vessels were noted in only three patients with optic atrophy and only two patients with optic disc edema. One patient had bilateral optociliary shunt vessels due to bilateral optic nerve sheath meningiomas. Optociliary vessels were late findings usually associated with severe degrees of venous engorgement (Fig 2, bottom right). Associated findings. One patient had neurofibromatosis but had no evidence of intracranial involvement

at presentation. There were only two patients who presented with concurrent intracranial involvement. In one patient the optic canal was enlarged, the clinoids were eroded, and a small sphenoid mass was demonstrated on CT scan. The other patient had two large masses at the tuberculum sellae and ipsilateral subfrontal region with sclerosis of the optic canal demonstrated by tomography. Both patients underwent craniotomy. Radiographic findings. Transfemoral angiography was performed in seven cases, and revealed a vascular blush in five. Tomograms of the optic canal were performed in ten patients. Four of these ten demonstrated enlargement of the optic canal, in one case with hyperostosis. Another patient demonstrated hyperostosis without enlargement, and five of ten were entirely normal. Both patients with intracranial involvement at presentation demonstrated hyperostosis alone or enlargement of the canal with hyperostosis. Tomographic abnormalities of the optic canal did not always correlate with intracranial involvement by CT. Computerized tomography demonstrated three characteristic patterns of optic nerve enlargment (Figs 3, 4). Tubular thickening of all or part of the intraorbital optic nerve was most common (64%). Fusiform enlargement usually involving the middle or posterior portion of the nerve was present in 23% (Fig 3). Finally 23% demonstrated anterior or posterior globular peroptic masses (Fig 4). The optic nerve could sometimes be identified as a central linear lucency through the mass. We did not observe calcification of the optic nerve in our patients. The posterior apical portion of the optic nerve was the most common site of involvement (81%) among all patterns of enlargement. There did not appear to be any correlation between the pattern or location of optic nerve enlargement and visual function. Globular masses, however, were usually associated with more severe degrees of proptosis. Natural history. The follow-up ranged from one to eight years (mean, 2'h years). All patients had progressive decline in visual acuity. In 82%, decline was gradual, typically manifesting a loss of one to three Snellen lines

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per year. One patient, however, dropped from 20/20 to 20/30 over an eight-year period of follow-up. Four patients suffered periods of rapid decline over a two- to three-month period. A decline in visual acuity (or visual field) was often accompanied by signs of chronicity in those patients with optic disc edema. Depending on the type of visual field defect at presentation progression occurred along several parallel lines (Fig 1). Those who presented with isolated enlargement of the physiologic blind spot subsequently developed one of three patterns of progression: ( 1) three of seven developed irregular peripheral constriction, (2) one of seven subsequently developed an inferonasal step, and (3) two patients showed a progressive enlargement of the blind spot encroaching on fixation (ie. ceocentral scotoma). Patients who presented with or subsequently developed an inferonasal step progressed by altitudinal extension towards the blind spot, giving rise to a large inferonasal quadrantic defect with baring of the blind spot. One of these patients was ultimately left with residual islands of vision in the temporal and nasal mi
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the disc, hyperemia and venous congestion was followed by increasing disc elevation, intrapapillary microvascular abnormalities and circumpapillary retinal folds. This was sometimes associated with the onset of transient visual obscurations. Progressive optic disc edema was not always associated with any significant visual decline. Chronicity was manifested by an apparent decrease in the degree of disc elevation, less hyperemia, yellowish discoloration of the disc (gliosis), refractile bodies (Fig 2, top), and in some cases sectoral areas of pallor. The presence of refractile bodies and other signs of chronicity correlated with decline in visual function. Refractile bodies tended to disappear as optic atrophy supervened. Venous congestion tended to persist despite the onset of optic atrophy, although decompression or excision of the tumor resulted in a notable absence or lessening of venous congestion. Circumpapillary retinal folds tended to resolve with the development of optic atrophy but infrequently persisted. Optociliary vessels become more evident with the development of optic atrophy. Intracranial involvement developed in three patients during follow-up. One patient demonstrated erosion of the clinoid and a sphenoid mass two years after presentation. This was associated with a rapid decline in her acuity and visual fields. The second patient, three years after presentation, developed a falx meningioma and an anterior cerebral artery aneurysm. The third patient with neurofibromatosis developed erosion of the clinoid with deformation and sclerosis of the optic strut four years after his initial examination. Because of relatively mild visual dysfunction and reluctance on the part of the patient to undergo surgery we are following this patient closely. All of the other patients underwent craniotomy and were histologically shown to have intracranial meningiomas. Intervention. Detailed information on treatment and follow-up will not be dealt with at this time. A brief summary is provided here. Two patients with a vision of hand motion or worse underwent fine needle aspiration biopsy for confirmation of the diagnosis. There was no observable alteration in visual function immediately following the procedure. Three patients underwent lateral orbitotomies for biopsy; two of which were done prior to our evaluation. Four patients with intracranial extension underwent craniotomies. These patients are maintaining their preoperative vision six months to four years later. Two other patients underwent transcranial orbitotomies for apically located tumors. In one patient the optic canal and orbit were unroofed with total excision of the nerve and tumor. The other patient underwent a subtotal resection of the intraorbital optic nerve tumor. Eight patients underwent extended lateral orbitotomies with partial or complete tumor excision and sparing of the optic nerve. This group of eight patients includes three of the patients who also underwent craniotomy. Postoperatively, six of the eight were improved in either acuity or visual field or both. Within several months to a year following surgery, however, three of the six resumed a slow decline in visual function. One of these 1319

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has been irradiated with no apparent improvement. The most dramatic result was in a 48-year-old woman with an unusual anteriorly located tumor, vision of counting fingers and loss of the inferior hemifield, who postoperatively recovered 20/20 vision and a full field. This result has now been maintained for five years. Extradural origin could not be ruled out. This patient was the subject of a previous report. 4 Finally, two patients each received 5000 rad to the orbit. One patient was treated prior to our evaluation improving from 20/70 to 20/30 and is maintaining acuity and field three years later. After four months the second patient's vision improved from 20/40 to 20/ 30+. The visual field which showed peripheral constriction improved after radiotherapy.

DISCUSSION The increased prevalence of meningiomas among women is well-established. Numerous studies have shown a remarkably constant gender ratio in patients with optic nerve sheath meningiomas with the proportion of females in several series ranging from 71% to 84%. 1- 3·13- 15 In our series, 68% were women. Most of our patients were 35 to 60 years old, consistent with other series. 1- 3·8 The occurrence of optic nerve sheath meningiomas in young patients has been well documented, but the incidence remains difficult to determine. 1·8·14 Childhood optic nerve sheath meningiomas may differ from the adult form. They are said to be more commonly associated with neurofibromatosis, and to be more invasive. 1·8·14·16 Since there were no children in our cohort the clinical characteristics described in this series reflect the behavior of adult onset optic nerve sheath meningiomas. Transient visual loss appears to be a common early symptom of optic nerve sheath meningiomas, frequently associated with optic disc edema. Two forms occurred: (I) "transient visual obscurations" characterized by fleeting, recurrent blackouts, lasting seconds (observed in 32% of our patients), and (2) duction induced "transient monocular blindn~ss" lasting minutes (observed in one patient). Wright2·3 has reported both types in optic nerve sheath meningiomas. Several case reports have documented transient visual obscurations in this disorder.9·17·18 The frequency of TVOs may reflect the high frequency of patients with optic disc edema among our cohort. TVOs are characteristic in patients with papilledema but may occur with any form of optic disc edema. The clinical features ofTVOs in papilledema and optic nerve sheath meningiomas are similar. 20 A distinctive feature, however, was noted by one of our patients whose TVOs would start or increase in frequency with elevation of her eye. Changes in eye position may also result in transient blindness. Wright2· 3 demonstrated interruption of retinal artery perfusion with fluorescein angiography, during abduction induced monocular blindness. The 1320

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mechanism of transient visual obscurations in papilledema however is not quite as clear. Hayreh 20 observed the fundus during TVOs and could not detect any retinal vascular abnormalities. Cogan21 postulated that obscurations were due to transient ocular ischemia. Hayreh 20 elaborated by noting that optic disc edema induces prelaminar circulatory stasis which results in a "critical balance" between disc perfusion and surrounding tissue pressure. Any factor such as change in posture, intraocular hypertension or contraction of the extraocular muscles may result in momentary disturbances of nerve conduction due to ischemia. Alternatively, it has been suggested that direct compression of the chiasm by a distended third ventricle may intermittently disrupt nerve conduction. 20·22 Sixty-eight percent of our patients had proptosis. Previous authors have noted a similar frequency ranging from 67 to 90%. 2·3·8 Despite its frequency as a sign we did not find proptosis to be a common presenting symptom. One patient presented with complaints of proptosis only and another complained of proptosis with mild antecedent visual loss. Both patients had large globular tumors with 5 to 6 mm of proptosis. These patients demonstrate that extradural growth may occur without significant nerve compression. 2·8 Previous reports have documented patients with normal or only mildly impaired acuity and optic disc edema as an early sign of optic nerve sheath meningiomas.5-7·9·12·16-18·23 The reported frequency of such patients varies from 15 to 26%. 2·3 Hendersen8 has reported mild visual acuity loss in 48% of his patients with lateral sphenoid wing tumors extending into the orbit. We observed mild visual impairment in 45% of our patients, a higher frequency than most previous reports. Our patients frequently had other signs of optic nerve compression such as proptosis, afferent pupillary defects, dyschromatopsia or ophthalmoplegia; however, three patients had normal pupils and color vision. The frequency of mild visual impairment among our cohort is probably the result of earlier diagnosis made possible by high resolution CT. Other factors include selection bias, an increasing awareness among ophthalmologists, and patient factors in seeking earlier medical attention. Despite the frequent occurrence of "normal" Snellen acuities, most of our patients complained of a subjective alteration in vision. The limitations of Snellen acuity in detecting subtle abnormalities in visual function has recently been emphasized. 24 Kupersmith25 has shown a decrease in contrast sensitivity among patients with optic nerve compression despite normal acuities, color vision and fields. Contrast sensitivitiy may be an important adjunct in the evaluation of patients with unilateral optic disc edema and normal Snellen acuity. In the early stages of optic nerve compression, optic nerve sheath meningiomas may be difficult to diagnose. Other clinical entities may present with normal or mildly impaired acuity, unilateral optic disc edema, and enlargement of the blind spot. This triad may occur in papillophlebitis26 ("big blind spot syndrome"), 27 disc

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drusen, 28 incipient ischemic optic neuropathy, 29 diabetic papillopathy, 28 •30 dysthyroid optic neuropathy, 31 optic perineuritis, congenital pseudodisc edema, cyanotic congenital heart disease, assymetric papilledema, unilateral papilledema (with congenital absence of one optic nerve sheath), cavernous hemangiomas and rickettsial infections. 28 A careful examination and history should allow the clinician to distinguish among these numerous possibilities. Several reports of optic nerve sheath meningiomas suggest that central scotomas are the most common visual field defect. 3 •8•23 •32 Chamlin, 35 however, noted that central scotomas without peripheral involvement are not nearly as frequent in compressive optic neuropathies as the literature implies. In his experience peripheral defects with accompanying or subsequent central involvement as a direct extension of a peripheral defect was more typical. Peripheral constriction may be less common but has been reported with orbital, optic canal and intracranial meningiomas. 32 Several case reports have documented early enlargement of the blind spot or peripheral constriction. 5 •6 •11 •16•18 •23 Central or cecocentral scotomas in our series were uncommon. In the early stages, enlargement of the physiologic blind spot was the most common defect. As nerve compression progressed the peripheral isopters constricted. If one considers patients with residual islands of vision (as an extreme manifestation of peripheral constriction), nearly all our patients ultimately developed peripheral constricting defects at some point in their course, including those patients with cecocentral scotomas. The central and peripheral field loss is probably the result of structural and ischemic effects on the nerve at the site of tumor compression. Occasionally, however, peripheral changes maintained respect for the horizontal meridian resulting in altitudinal inferonasal steps. The occurrence of similar field defects in ischemic optic neuropathy, drusen, papilledema and glaucoma suggests that prelaminar injury due to chronic disc edema may also play a role in the vision loss with optic nerve sheath meningioma. It has been suggested that regional differences in laminar nerve head anatomy may increase the vulnerability of axons which subserve the peripheral inferonasal isopters. 33•33a The evolution of visual field loss from enlargement of the blind spot to residual islands of vision seems to proceed along several parallel stereotyped pathways. These patterns are schematically depicted in Figure 1. The overlapping patterns of progression among our cohort suggests that patients who presented with islands of vision may have deteriorated along similar lines. Hollenhorst7 has reported nine patients with optic nerve sheath meningiomas and documented similar field defects and patterns of progression. Our experience with optic nerve sheath meningiomas confirms Chamlin's35 impression that the most common sign of prechiasmal nerve compression is peripheral constriction. Changes in the optic nerve head were consistently present among our patients, manifested primarily as

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optic disc edema or optic atrophy. Patients with optic disc edema generally had milder degrees of visual dysfunction. Deteriorating visual function in patients with optic disc edema often correlated with signs of chronicity marked by an apparent decrease in the degree of swelling, decreasing hyperemia, gliosis, optociliary shunt vessels, and intrapapillary refractile bodies. Certain ophthalmoscopic findings should arouse suspicion of an optic nerve sheath meningioma. We already noted the differential diagnosis of unilateral optic disc edema with normal Snellen acuities. Optic disc edema with choroidal folds should also suggest the possibility of a nerve sheath meningioma. A more specific finding is the presence of optociliary shunt vessels with optic atrophy. This sign has been well described and emphasized in the recent literature. 9 - 12 Its occurrence in middle aged women with longstanding visual loss is typical of spheno-orbital meningiomas. This triad was seen in only 5 of 22 patients in our series. We found optociliary shunt vessels to be a late finding, but occasionally seen in patients still with optic disc edema. Tumor compression of the central retinal vein may result in retinal venous shunting thru preexistent capillary channels that drain into the peripapillary choroid. A more subtle (but less specific) funduscopic finding of the same underlying mechanism that results in optociliary vessels, was optic atrophy with marked venous congestion. Optociliary vessels may also occur with chronic atrophic papilledema, optic disc drusen, retinal vein occlusions, and glaucoma, or may be congenital. 9 Our study suggests that unilateral chronic disc edema with refractile bodies may be another important but nonspecific manifestation of optic nerve sheath meningioma. Surprisingly refractile bodies occurred in 7 of 13 patients with optic disc edema. Refractile bodies were characteristically quite small and never seemed to attain the appearance of large refractile concretions typical of hyaline bodies of the optic disc. In addition, refractile bodies (unlike hyaline bodies), usually disappeared with the development of optic atrophy. It is also possible, however, that gliotic changes in the nerve head may prevent their visualization. Refractile bodies have been reported in patients with chronic papilledema and melanocytomas. 19•28 It is probable that any condition resulting in chronic disc edema will lead to their formation and may explain their absence in ischemic or inflammatory optic neuropathies. Several authors have commented on the significance of these deposits in patients with papilledema. Miller 8 states that if these refractile bodies ("hard exudates") are present "one may assume that papilledema has been present for several months." This would seem to apply in our cases since refractile bodies were only seen among those patients with optic disc edema after one year of observation or at least one year of symptoms. Their similarity to hyaline bodies with pseudo-optic disc edema has sometimes lead to confusion in the diagnosis of chronic papilledema with intracranial hypertension. 36 Some investigators have reported an association between 1321

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hyaline bodies and meningiomas. 37-39 However, this association may have been fortuitous. Alternatively, like Okun's36 patient with chronic papilledema, refractile bodies in optic nerve sheath meningiomas may be confused with hyaline bodies of the disc. We found high resolution CT indispensible in the early diagnosis and followup of optic nerve sheath meningiomas. High resolution CT can define the extent of optive nerve enlargement and detect most cases with intracranial extension. Optimum visualization requires proper axial orientation combined with coronal cuts. With conventional axial views the sinuous course of the intraorbital optic nerve can produce oblique sections. This problem can be circumvented by orienting axial cuts at -20° with the eyes in 40° of elevation. This will incorporate the entire length of the optic nerve in one plane of section. 40 The patterns of optic nerve enlargement observed in our series is similar to those in previous reports.'- 3·41 They include diffuse tubular thickening, fusiform enlargement and globular perioptic enlargement. These patterns of thickening primarily involve the apical segment of the nerve, although any portion may be affected. Occasionally globular masses demonstrated central linear lucencies. There was no discernible correlation between pattern or location of thickening and visual function. Not surprisingly those patients with globular perioptic masses were much more likely to have significant proptosis. High resolution CT sans permit earlier diagnosis and may account for the frequent occurrence of mild visual impairment in our cohort. Calcification of the optic nerve, particularly in a ring like distribution, appears to be a specific radiographic sign of optic nerve sheath meningiomas. 42 This sign is rare and usually occurs as a very late feature. 8·41 ·43 Calcification was not observed in our cohort. We should emphasize that optic nerve thickening seen on CT scan may be observed with other diseases including optic nerve glioma, optic neuritis, perineuritis (due to sarcoidosis, syphillis and pseudotumor), arachnoid cyst, perineural hematoma, and meningeal carcinomatosis.34·41 Six patients were included in our study on the basis of a clinical diagnosis and identified as such in Table 1. Their clinical characteristics and progression did not significantly differ from those patients with a biopsy proven diagnosis. The increased sensitivity of high resolution CT has obviated the need for radiographic studies in detecting canalicular or intracranial involvement. However with earlier low resolution scans canalicular and en plaque sphenoid meningiomas may be overlooked. 8·17·44 •46 Where experienced high resolution CT scanning is not available, complex motion polycycloidal tomography remains an important adjunct in the diagnosis of perioptic meningiomas. Optic canal tomography may show enlargement, erosion, sclerosis, and calcification. There are, however, important limitations to roentgenographic techniques in the detection ofoptic nerve sheath meningiomas. 6·8·13·17·23·45

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Ten to 36% to sphenoidal and intraorbital meningiomas are radiographically negative. 46 Kennerdell and Maroon6 reported an intracanalicular meningioma with normal plain and optic foramen roentgenograms. Susac45 reported a canalicular meningioma with normal optic canal tomography detected by CT scan. The importance of early diagnosis and close follow-up of optic nerve sheath meningiomas is to prevent the development of an unresectable intracranial component. Intracranial involvement occurred in 5 of 22 patients (23%) over a one to eight-year follow-up. Alper' noted a similar frequency. Two of our patients demonstrated intracranial involvement at the time of presentation, and three subsequently developed CT evidence of intracranial extension two to four years after presentation. One of the latter patients had neurofibromatosis. In addition, two of our patients had bilateral optic nerve sheath meningiomas without CT scan evidence of extension. While multicentric origin may explain the occurrence of bilateral involvement,2·18·47 intracranial interconnection is difficult to rule out. Trobe46 reported a case of bilateral optic canal meningiomas without detectable interconnection radiologically. However, on microscopic inspection, tumor was found on the planum and confirmed by biopsy. Most cases of bilateral perioptic meningiomas occur via intracranial extension or by involvement of both nerves from a common basofrontal or sphenoid tumor. 8·38 ·46·48 Early detection of optic nerve sheath meningiomas is essential since primary or secondary intracranial involvement can occur as an early or late finding. We can summarize the early clinical features of optic nerve sheath meningiomas. Transient visual obscurations are common. These may precede, follow, or develop simultaneously with visual loss. They are associated with optic disc edema and can occasionally be induced or exacerbated by eye movement. Subjective decrease in vision is the most common presenting complaint despite normal or only mildly impaired acuity. There are often other signs of optic neuropathy, such as dyschromatopsia and afferent pupillary defects. Occasionally, however, these signs may be absent. The most consistent visual field defect is peripheral constriction. The earliest defect consists of isolated enlargement of the blind spot. Peripheral changes may sometimes respect the horizontal meridian. Less commonly cecocentral scotomas occur with peripheral constriction. Optic disc edema is frequently observed in the early stages of nerve compression. With time, chronic disc edema associated with intrapapillary refractile bodies develop. Optic disc edema oftentimes precedes the development of optic atrophy. Decline in acuity and visual fields is slow and relentless, progressing over months to years. Intervention must therefore be restrained by the possibility that some patients deteriorate very slowly. We usually follow these patients with biannual neurophthalmological examinations to monitor visual decline and annual CT scans for

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detection of intracranial extension. We suggest biopsy confirmation of the diagnosis in those patients with profound vision loss, rapidly deteriorating vision or intracranial extension.

ACKNOWLEDGMENTS The authors thank those physicians who referred many of the patients included in this study, specifically Dr. Robert S. Hepler and Dr. William T. Shults for referring patients with bilateral optic nerve sheath meningiomas. Dr. Simmons Lessen provided comments on the manuscript.

REFERENCES 1. Alper MG. Management of primary optic nerve sheath meningiomas. Current status-therapy in controversy. J Clin Neuro-Ophthalmol 1981; 1:101-17. 2. Wright JE. Primary optic nerve meningiomas: clinical presentation and management. Trans Am Acad Ophthalmol Otolaryngol 1977; 83:0P617-25. 3. Wright JE, Call NB, Liaricos S. Primary optic nerve meningioma. Br J Ophthalmol 1980; 64:553-8. 4. Mark LE, Kennerdell JS, Maroon JC, et al. Microsurgical removal of a primary intraorbital meningioma. Am J Ophthalmol 1978; 86:704-9. 5. Smith JL, Vuksanovic MM, Yates BM, Bienfang DC. Radiation therapy for primary optic nerve meningiomas. J Clin Neuro-Ophthalmol 1981; 1:85-99. 6. Kennerdell JS, Maroon JC. lntracanalicular meningioma with chronic optic disc edema. Ann Ophthalmol1975; 7:507-12. 7. Hollenhorst RW Jr, Hollenhorst RW Sr, MacCarty CS. Visual prognosis of optic nerve sheath meningiomas producing shunt vessels on the optic disc. Mayo Clin Proc 1978; 53:84-92; Also: Trans Am Ophthalmol Soc 1977; 75:141-63. 8. Hendersen JW. Orbital Tumors, 2nd ed. New York: Brian C. Decker, 1980; 472-96. 9. Boschetti NV, Smith JL, Osher RH, et al. Fluorescein angiography of optociliary shunt vessels. J Clin Neuro-Ophthalmol 1981; 1:9-30. 10. Fris€m L, Hoyt WF, Tengroth BM. Optociliary veins, disc pallor and visual loss; a triad of signs indicating spheno-orbital meningioma. Acta Ophthalmol 1973; 51 :241-9. 11. Ellenberger C. Perioplic meningiomas: syndrome of long-standing visual loss, pale disk edema, optociliary veins. Arch Neural 1976; 33:671-4. 12. Spencer WH. Primary neoplasms of the optic nerve and its sheaths: clinical features and current concepts of pathogenetic mechanisms. Trans Am Ophthalmol Soc 1972; 70:490-528. 13. Craig WMcK, Gogela LJ. Intraorbital meningiomas; a clinicopathologic study. Am J Ophthalmol 1949; 32:1663-80. 14. Karp LA, Zimmerman LE, Borit A, Spencer W. Primary intraorbital meningiomas. Arch Ophthalmol1974; 91:24-8. 15. Reese AB. Tumors of the Eye, 3d ed. New York: Harper & Row, 1976; 148-53. 16. Walsh FB. Meningiomas, primary within the orbit and optic canal. In: Smith JL, ed. Neuro-Ophthalmology Symposium of the University of Miami and the Bascom Palmer Eye Institute. StLouis: CV Mosby, 1970; Vol 5:240-66.

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17. Susac JO, Smith JL, Walsh FB. The impossible meningioma. Arch Neurol 1977; 34:36-8. 18. Hart WM Jr, Burde RM, Klingele TG, Perlmutter JC. Bilateral optic nerve sheath meningiomas. Arch Ophthalmol 1980; 98:149-51. 19. Spencer WH. Drusen of the optic disc and aberrant axoplasmic transport. Am J Ophthalmol 1978; 85: 1-12; also: Ophthalmology 1978; 85:21-38. 20. Hayreh SS. Optic disc edema in raised intracranial pressure. VI. Associated visual disturbances and their pathogenesis. Arch Ophthalmol 1977; 95:1566-79. 21. Cogan DG. Blackouts not obviously due to carotid occlusion. Arch Ophthalmol 1961; 66:180-7. 22. Paton L. A clinical study of optic neuritis in its relationship to intracranial tumours. Brain 1909; 32:65-91. 23. Wilson WB, Gordon M, Lehman RA. Meningiomas confined to the optic canal and foramina. Surg Neural 1979; 12:21-8. 24. Bodis-Wollner I, Camisa JM. Contrast sensitivity measurement in clinical diagnosis. In: Lessell S, van Dalen JTW, eds. NeuroOphthalmology; a Series of Critical Surveys of the International Literature. Amsterdam: Excerpta Medica, 1980; vol. 1: 373-401. 25. Kupersmith MJ, Siegel IM, Carr RE. Subtle disturbances of vision with compressive lesions of the anterior visual pathway measured by contrast sensitivity. Ophthalmology 1982; 89:68-72. 26. Hayreh SS. Optic disc vasculitis. Br J Ophthalmol 1972; 56: 652-70. 27. Miller NR. The big blind spot syndrome: unilateral optic disc edema without visual loss or increased intracranial pressure. In: Smith JL, ed. Neuro Ophthalmology Update. New York: Masson, 1977; 163-9. 28. Miller NR. Walsh and Hoyt's Clinical Neuro-Ophthalmology, 4th ed. Baltimore: Williams & Wilkins, 1982. 29. Hayreh SS. Anterior ischemic optic neuropathy. V. Optic disc edema as early sign. Arch Ophthalmol1981; 99:1030-40. 30. Lubow M, Makley TA Jr. Pseudopapilledema of juvenile diabetes mellitus. Arch Ophthalmol 1971; 85:417-22. 31. Trobe JD, Glaser JS, LaFlamme P. Dysthyroid optic neuropathy; clinical profile and rationale for management. Arch Ophthalmol1978; 96:1199-209. 32. Wilson WB. Meningiomas of the anterior visual system. Surv Ophthalmol1981; 26:109-27. 33. Quigley HA, Addicks EM. Regional differences in the structure of the lamina cribosa and their relation to glaucomatous optic nerve damage. Arch Ophthalmol1981; 99:137-43. 33a.Radius RL. Regional specificity in anatomy at the lamina cribosa. Arch Ophthalmol 1981; 99:478-80. 34. Howard CW, Osher RH, Tomsak RL. Computed tomographic features in optic neuritis. Am J Ophthalmol 1980; 89:699-702. 35. Chamlin M. Visual field defects due to optic nerve compression by mass lesions. Arch Ophthalmol 1957; 58:37-58 .. 36. Okun E. Chronic papilledema simulating hyaline bodies of the optic disc; a case report. Am J Ophthalmol 1962; 53:922-7. 37. Harms H. Fall von Drusenpapillen. Abstract. Klin Monatsbl Augenheilkd 1960; 136:122. 38. Rucker CW, Kearns TP. Mistaken diagnoses in some cases of meningioma; clinics in perimetry no. 5. Am J Ophthalmol 1961; 51:15-9. 39. Ben Zur PH, Lieberman TW. Drusen of the optic nerves and meningioma: a case report. Mt Sinai J Med 1972; 39:188-96. 40. Unsold R, Newton TH, Hoyt WF. CT examination technique of the optic nerve. J Comput Assist Tomogr 1980; 4:560-3. 41. Rothfus WE, Curtain HD, Slamovits TL, Kennerdell JS. Optic nerve/ sheath enlargement; a differential approach based on high-resolution CT morphology. Radiology 1984; 150:409-15. 42. Cohn EM. Optic nerve sheath meningioma; neuroradiologic findings. J Clin Neuro-Ophthalmol1983; 3:85-9.

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43. Lloyd GAS. The radiology of primary optic nerve sheath meningioma. Br J Radiol1971; 44:405-11. 44. Wright JE, Lloyd GAS, Ambrose J. Computerized axial tomography in the detection of orbital space-occupying lesions. Am J Ophthalmol 1975; 80:78-84. 45. Susac JO, Martins AN, Whaley RA. lntracanalicular meningioma with normal tomography. J Neurosurg 1977; 46:659-62.

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46. Trobe JD, Glaser JS, Post JD, Page LK. Bilateral optic canal meningiomas: a case report. Neurosurgery 1978; 3:68-74. 47. Craig WMcK, Gogela LJ. Meningioma of the optic foramen as a casue of slowly progressive blindness; report of 3 cases. J Neurosurg 1950; 7:44-8. 48. Kearns TP, Wagener HP. Ophthalmologic diagnosis of meningiomas of the sphenoidal ridge. Am J Med Sci 1953; 226:221-8.

Discussion

by Neil R. Miller, MD Sibony and associates have described the characteristics of 22 patients with optic nerve sheath meningiomas. Although the paper is concise and complete, there are several points that I would like to address. First, I believe that bilateral optic nerve sheath meningiomas are primarily a disorder of young adults. All of the five patients that I have examined with bilateral optic nerve sheath meningiomas have been under 20 years of age, and it is interesting that the youngest patient in this series-18 years of age-was one of two patients with bilateral meningiomas. Of course, the finding of bilateral meningiomas in a 48-year-old woman shows that they may occur at any age. Nevertheless, I believe that the differential diagnosis of bilateral, progressive optic neuropathy in a young patient should include bilateral optic nerve sheath meningiomas. I agree with Sibony et al that some patients with optic nerve sheath meningiomas occasionally complain of transient visual obscurations, as do patients with the big blind spot syndrome (papillophlebitis; optic disc vasculitis). The occurrence of transient visual obscurations in such patients suggests to me that the etiology of such symptoms-even in patients with papilledema and increased intracranial pressure-is local and probably vascular, not intracranial compression as suggested by some investigators in the past. The authors have appropriately emphasized the relatively mild degree of visual acuity loss associated with optic disc swelling that occurs early in patients with optic nerve sheath meningiomas. Although such patients invariably complain of visual problems, the fact that they have relatively intact visual acuity may obscure the presence of a significant optic neuropathy unless other tests, such as color vision, visual fields, and pupillary function are performed. Thus, when an incomplete examination is performed, the differential diagnosis of a patient with "normal" vision and optic disc swelling should include an optic nerve sheath meningioma. Since most physicians are more concerned about an intracranial process (eg. unilateral papilledema-increased intracranial pressure), computed tomography (CT) scans ordered in such patients often do not include thin section orbital cuts, and thus miss the lesion. Common causes of optic disk swelling are papilledema and compressive ·optic neuropathy. Less common causes include optic perineuritis, infiltrative optic neuropathy, ischemic optic neuropathy, and ocular inflammatory syndrome. With respect to color vision testing, the authors found that 27% of their patients were able to correctly identify all of the

Ishihara color plates with their involved eye. This, of course, does not imply that their color vision was normal. Many patients with mild optic neuropathy, particularly those with recovered optic neuritis, may be able to identify the color plates correctly, but they will do so noticeably more slowly with the involved eye than with the normal eye. In addition, such patients, when shown a red target with each eye separately, will usually be aware of a relative desaturation to red when viewing the target with the involved eye. Finally, patients with "normal" color vision on color plates may show grossly abnormal color perception when tested with a FarnsworthMunsell Dl5 or D85 test. Thus, I would suspect that, had the

From the Neuro-ophthalmology Unit, The Wilmer Institute, The Johns Hopkins Medical Institutions, Baltimore.

Fig I. The visual field as an "island of vision surrounded by blindness," as described by Traquair.

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Dura

Arachnwcl

Fig 3. Gross appearance of an optic nerve sheath meningioma. Note that it is entirely intradural.

Fig 2. The structure of the optic nerve. Note that there is no dural covering intracranially.

patients examined by Sibony et al been tested more extensively, they would have been found to have abnormal color perception in their involved eyes. Similarly, I suspect that the three patients who were said not to have afferent pupillary defects probably did have abnormalities of pupillary function. In some patients with unilateral, mild optic neuropathies, I have found it difficult to diagnose an afferent pupillary defect. In such patients, the pupil on the involved side may show pathologic pupillary unrest and may dilate faster than the pupil on the opposite side after being constricted with a bright light. Such patients may also have a subjective afferent defect in the involved eye, complaining, if asked, that the light is 'not as bright when shined in the involved eye as when it is shined in the normal eye. Again, therefore, I suspect that pupillary function was in fact probably abnormal in all the patients studied by Sibony et al. It is significant that 59% of patients in this series had proptosis of only 2 to 4 mm. This mild degree of proptosis is another reason that patients with unilateral optic disc swelling, particularly when referred to a neurologist or neurosurgeon, are often not suspected of having an orbital process. Neuroradiologic tests that are performed on such patients thus often do not include careful examination of the orbit. The finding that the most common visual field defect in patients with optic nerve sheath meningioma is generalized peripheral constriction is not surprising. If one considers the visual field, as did Traquair, 1 as an island of vision surrounded by blindness, with the height of the island the measure of

Fig 4. Microscopic appearance of an optic nerve sheath meningioma showing its location between the pia-arachnoid and the dura.

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visual sensitivity, then it is clear that generalized erosion of the island will produce decreased central vision associated with peripheral field constriction but without a central scotoma (Fig 1). It should be recognized, however, that central scotomas can occur with compressive lesions of the optic nerve. There is virtually no visual field defect that, in and of itself, rules out an intracranial lesion. It is clear that CT scan using thin section axial and coronal techniques is the best way to identify optic nerve sheath meningiomas. We have been impressed, in addition, with the radiologic sign known as pneumosinus dilatans, a marked expansion of the posterior ethmoid and sphenoid sinuses, as a sign of intracranial or intracanalicular meningioma (Hirst et ae· 3). I wonder if any of the patients described by Sibony and co-workers showed this sign on either plain skull x-rays or CT scan? The authors state that they "do not address the controversial issues of treatment in this report." Unfortunately, in their discussion of surgical intervention, they have chosen to include a case that is so exceptional that I must consider it. This is the case, previously reported by Mark et al, 4 of a 48-year-old woman who had complete return of visual acuity and visual field after removal of a primary orbital meningioma wrapped in a C-shape around the anterior portion of the optic nerve. Meningiomas involving the orbital optic nerve arise from the area between the arachnoid and the dural sheaths of the optic nerve or grow into this space from intracranially (Figs 2-4). They do not arise from the external surface of the nerve. Thus, the tumor described by Mark et al either grew through a hole in the dura at the point of development, or it was not a meningioma of the optic nerve sheath at all: possibly (as has been suggested by Jakobiec 5) it was derived from one of the ciliary nerves adjacent to the optic nerve. These nerves may have small arachnoid cell rests around them. In any event,

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this case should in no way be considered an optic nerve sheath meningioma. Sheath meningiomas are simply not removable in their entirety from the optic nerve without sacrificing the nerve. They are wrapped completely around the nerve and usually extend posteriorly into "no man's land" in the region of the annulus of Zinn. Thus, while one may buy some time for vision by attacking these lesions, one should not operate under the assumption that complete removal-sparing the optic nerve-will be possible. I certainly do agree with Sibony et al that once vision is lost, complete removal of nerve and tumor is advisable as soon as possible to prevent intracranial involvement. The authors have provided us with a clear picture of the clinical manifestations of patients with optic nerve sheath meningiomas. The first step in the management of any problem is its recognition. Using the methods outlined in this paper we should be able to diagnose this condition without difficulty. The real difficulty begins once the diagnosis is made, and, at present, our management of these lesions leaves much to be desired. References 1. Harrigton D. The Visual Fields. 4th ed. St. Louis: C.V. Mosby, 1976. 2. Hirst LW, Miller NR, Allen GS. Spenoidal pneumosinus dilatans with bilateral optic nerve meningiomas; case report. J Neurosurg 1979; 51:402-7. 3. Hirst LW, Miller NR, Hodges FJ Ill, et al. Sphenoid pneumosinus dilatans; a sign of meningioma originating in the optic canal. Neuroradiology 1982; 22:207-10. 4. Mark LE, Kennerdell JS, Maroon JC, et al. Microsurgical removal of a primary intraorbital meningioma. Am J Ophthalmol1978; 86:704-9. 5. Jakobiec F. Personal Communication. 1983.