Exophthalmos Outcome

Postoperatively, proptosis improved in nine (64.3%) and remained static in the rest five (35.7%) of patients (Table 3). None of our patients developed enophthalmos due to excessive bony or soft tissue decompression. It was observed that improvement in proptosis was better when the decompression of the orbital walls, especially the lateral orbital, was adequately performed. This was well appreciated in two of our patients who underwent resurgery for recurrence and the lateral orbital wall drilling was performed extensively (Fig. 3). We did not observe any close relation between periorbital removal and improvement in proptosis. Since bony or plate reconstruction was not performed in any of our patients, its influence on proptosis could not be assessed.

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Fig. 3 Postoperative computed tomography images of a patient. (A) Following extensive bony removal around the lateral orbital wall. (B) Following inadequate bone removal of the lateral wall sphenoid wing.

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Fig. 3 Postoperative computed tomography images of a patient. (A) Following extensive bony removal around the lateral orbital wall. (B) Following inadequate bone removal of the lateral wall sphenoid wing.

Visual Outcome

Four patients (28.6%) improved in vision following surgery. Vision remained static in eight patients (57.1%) and vision deteriorated in two (14.3%) in the postoperative period (Table 4). The two patients who deteriorated had primary optic atrophy and extremely poor vision preoperatively (restricted to hand movements). All the four patients who improved postoperatively were operated in the latter part of series where we used to perform OC deroofing and anterior clinoid process (ACP) routinely, irrespective of their involvement in imaging (Fig. 4).

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Fig. 4 Postoperative computed tomography images of a patient. (A) Following inadequate bony removal around the optic canal (OC) and anterior clinoid process (ACP). (B) Following removal of the ACP and OC deroofing.

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Fig. 4 Postoperative computed tomography images of a patient. (A) Following inadequate bony removal around the optic canal (OC) and anterior clinoid process (ACP). (B) Following removal of the ACP and OC deroofing.

Complications

We did not have any mortality in our series. One of our patients had to be reexplored for an extradural hematoma. New onset oculomotor palsy was noticed in three patients (17.6%), which persisted for nearly 6 months in two. Disabling facial hyperesthesia over the trigeminal distribution was seen in two patients, which was partially controlled with medications. Restricted ocular motility due to mechanical causes and not related to any nerve palsy was seen in six patients (35.3%). However, these disturbances improved with time.

Recurrence and Radiation Therapy

At mean follow-up of 3 years, of the 15 patients with residual lesions, the tumor showed progression in 10 (58.9%) and remained stable in the remaining 5. Three of these 10 patients had symptomatic recurrence warranting repeat surgery (17.4%), which was followed by radiotherapy. All the other seven patients were advised radiotherapy of whom only five completed it. All the three symptomatic recurrences requiring surgery occurred in patients with Grade II meningiomas. Patients with small residual/stable recurrences were kept under a close follow-up with serial imaging.

Outcome Predictors

Patients with relatively better preoperative vision fared better postoperatively as did patients with a symptom history of less than 2 years. However, we felt that liberal bony decompression of the lateral wall of orbit, OC, and ACP removal helps in visual improvement and reduction in proptosis. As the total number of patients in the series is small, statistical significance was difficult to obtain for any of the factors (Tables 5 6).

Symptomatology

Proptosis (45–100%) and progressive visual deterioration (30–77%) are the two most common presenting complaints of patients with SOM.5 7 8 18 19 Guiot et al divided SOMs into two categories.20 21 First, the pterional or external variety, which is associated with early exophthalmos and may cause decreased VA in the late stage. Second, the internal variety, which may cause optic nerve compression and visual deficits at presentation. Cranial nerve deficits, temporal swelling, and headache or retroorbital pain are other common symptoms of SOM.5 6 7 8 9 18 22

Reasons for proptosis are multifactorial.14 In addition to the osseous invasion of the tumor in the orbital walls, mass effect due to the intraorbital soft tissue component of the tumor and the reduction in venous drainage from the orbit result in proptosis.3 15 23 Scarone et al observed that radiological evidence of exophthalmos is always present even if it is not obvious clinically.3 Visual impairment is directly related to the tumor invasion into the orbit, especially in the orbital apex and OC region.8 24 Oculomotor nerve and trigeminal nerve involvements usually indicate extension of the tumor into the CS, SOF, and other basal foramina. Headache is seldom due to raised intracranial pressure as these lesions have a propensity to spread along the convexity and basal dura rather than into the brain parenchyma. The presenting symptoms in our series correspond with other published series except for the higher number of patients with visual impairment on presentation. This probably is related to the delay in presentation and larger size of tumor at presentation.

Radiology

SOMs need to be differentiated from orbital meningiomas and sphenoid wing meningiomas.25 26 Combination of extensive bony hyperostosis and orbital extension are distinct characteristic imaging features of SOM. The exact cause and mechanism of the bony hyperostosis is unclear and is a matter of debate. The current consensus is that it represents direct tumor invasion of the bone as several studies have confirmed histological tumor invasion in resected osseous specimens.3 23 27 28 SOMs thus qualify as tumors of the interperiosteodural concept.18 This indicates that hyperostosis essentially is a part of the neoplastic process and GTR implies removal of the entire affected bone, which is a formidable surgical challenge.1 29 30 Signal intensity changes in SOMs on MRI are similar to other meningiomas. SOMs, however, tend to breach the pia of the brain parenchyma, and the tumor brain interface is often not distinct on MR images. MR images may also reveal the increased vascularity of these tumors, essentially from external carotid supply.

Management

Surgery is the first line of management. The surgical technique needs to be customized based on the extent of the lesion. Standard frontotemporal craniotomy combined with additional orbital or zygomatic osteotomies in selected cases is the preferred approach by most authors.3 5 6 12 16 22 31 In addition, most authors concur that tumor invasion to the SOF as well as extension into the CS should constitute the limiting factors of radical resection and that the integrity of the periorbita should not be violated unless there is a discrete tumor involvement.3 6 10 12 14 Two aspects of the surgical technique remain controversial: The first debate involves the removal of ACP as an integral routine step in surgery. Involvement of ACP is seen in 5 to 56% of the cases,1 2 3 8 9 11 26 and hence few authors believe that anterior clinoidectomy and OC deroofing need be done only in affected patients.2 We share the opposite view and believe that ACP removal and OC deroofing improves visual outcome and should be included as a routine step in surgery.3 6 14 16 27 Selective rigid orbital reconstruction is another controversial surgical strategy. Multiple techniques and materials have been described for orbital reconstruction using both autologous and synthetic implants. Some authors favor a rigid reconstruction in all cases to avoid enophthalmos, ocular paresis, poor cosmesis, pulsatile exophthalmos, and pseudomeningocele.3 19 Others feel that reconstruction is unnecessary regardless of the extent of orbital wall removal. They argues that reconstruction is neither necessary for cosmesis nor for preventing pulsatile enopthalmos.6 10 12 32 A third view is that rigid reconstruction is necessary to achieve a good cosmetic result only if the periorbita is widely violated.2 31 In our small series of 17 cases, we have achieved reasonable cosmetic results without any rigid reconstruction.

Degree of Resection

Although Simpson’s Grade I resection with minimal morbidity remains the primary treatment goal, it is often impossible to accomplish without causing severe morbidity.1 7 9 Reported rates of GTR vary from 0 to 70%,2 3 7 11 16 and we could achieve GTR in only two of our patients. We believe in the general consensus that surgery should be “symptom-oriented.”3 5 6 8 Customized tumor resection helps to maximize VA outcomes and to improve proptosis in comparison to GTR. Decompression of the orbital walls, orbital apex, and OC should be aggressive. Resection in and around SOF, CS, and under the periorbita should be conservative.

Recurrence

Residual disease is common, but published recurrence rates for surgically resected SOMs, with and without radiation, ranges from 0 to 71%.1 7 16 19 The evolution of residual tumor is highly variable, with very slow regrowth in most cases or complete stability for years. The rate of SOM progression is not as rapid as that of malignant meningioma, but is comparable to that of other WHO Grade I meningiomas. Younger age at presentation (40s vs. 50s) was the only factor significantly associated with recurrence in Freeman’s cohort.8 Ho et al found that SOMs had a higher number of 1p and 6q deletions and this subtype more frequently progressed after STR.33 Long-term medical follow-up is essential, because the majority of recurrences appeared 6 years after the surgery.10 Tumor recurrence is significantly influenced by the extent of meningioma resection. Mariniello et al reported that the recurrence rate was greater after Simpson’s Grades III and IV resection than after Grade I resection.28 Surgical strategy aimed at maximal tumor resection with functional preservation provides an estimated 5- and 10-year progression-free survival (PFS) of 75 and 49%, respectively.10 14 We share Gonen et al’s view that the rate of growth of residual disease is slow.2 Despite a residual tumor in 48.2% of the cases, progression of residual tumor was slow and limited to 7.7%.

Outcome and Outcome Predictors

Literature reports on proptosis improvement vary from 60 to 96%.5 6 8 9 16 The main factors that influence postoperative exophthalmos regression are still not clear. Preoperative duration of symptoms, extent of orbital wall removal, especially the lateral wall, and the integrity of the periorbita have been postulated as leading factors.9 10 While some authors believe that periorbital removal is necessary for adequate improvement in proptosis,6 9 14 15 others like Oya et al prefer to maintain the periorbita for functional preservation.18 We believe in the middle path proposed by Nagahama et al, which is to tailor the resection—resect the invaded periorbita but do not perform reconstruction if the residual tumor is large.12 Although we believe that liberal lateral orbital wall removal up to the apex helps in proptosis reduction, we could not find any statistically significant relation in our series.

Visual improvement after SOM surgery ranges from 17 to 77%.7 12 16 31 32 As in Terrier’s series, in our series too, none of the patients’ characteristics—age, duration of symptoms, extent of proptosis, or surgical procedure—contributed to predicting the visual outcome.9 Gonen et al reported that preoperative visual deficit and OC involvement are significant parameters affecting favorable change in visual function after resection of SOM.2 We too strongly believe that decompression of the optic nerve is a mandatory step in SOM surgery and our findings support the concept that visual outcome is related to the extent of optic nerve decompression, rather than the extent of tumor resection. We observed that postoperatively vision worsened in two of our patients who had severe preoperative visual deficits. The probable reasons for this decline include intraoperative handling of an already compromised optic nerve, vascular compromise, and thermal injury during OC drilling. We believe that all orbital surgeons should be aware of this possible complication and need to be extra cautious in patients with severely affected vision.

Orbital Volume and Proptosis

Orbital volume assessment is important in orbital reconstruction, especially in orbital fractures and craniofacial anomalies.34 35 Reconstruction of the bony orbit is a challenge, following decompressive orbital surgeries. Several studies have recently been published on orbital volume assessment using 3D volumetric computational techniques.34 35 Their role in prognostication of proptosis following surgery for orbital pathologies like tumors have not been reported extensively. Current focus is more on restoration of orbital volume to improve aesthetics following surgery. Our study focused on the prognostic role of increase in orbital volume in improving proptosis. Our findings were not significant probably because of the small number of patients in the study.

Complications

Complications following SOM resection may include new onset cranial nerve deficits and ocular paresis due to mechanical restriction. Improvement in these new onset symptoms are often delayed, variable, and unpredictable.10 18 Restricted ocular motility due to mechanical causes usually happens in patients where aggressive attempt is made to free the tumor attached to the intraocular muscles. Keeping the periorbita open and being conservative with tumor adherent to the intraocular contents reduce this complication. New onset oculomotor palsy and trigeminal dysfunction can similarly be minimized by a conservative decompression around the SOF, CS, and basal foraminas.

Radiation Therapy

The role or timing of radiotherapy in SOM is controversial. Initially restricted to WHO Grade II and Grade III tumors, recent studies support the use of radiation therapy for subtotally resected Grade I meningiomas, demonstrating an overall and PFS advantage over surgery alone.3 6 36 Stereotactic radiosurgery (SRS) alone or in conjunction with fractionated intensity-modulated radiotherapy may be of particular benefit in treating SOMs.34 The optimal timing of radiation treatment (immediately after surgery or at recurrence) is still debated. Our current strategy is to recommend immediate postoperative radiotherapy for all Grade II and III meningiomas and patients with significant residue.

Limitations

The small number of patients in our series limits the possibility of arriving at any statistically significant conclusion with regard to predictors of outcome.