In patients with tuberculum sellae meningioma, preservation of the optic nerve is one of the most significant issues12). We report the rare case of a patient whose optic nerve was penetrated by a meningioma. Such cases require special attention in order to preserve the optic nerves.

A 68-year-old woman presented with decrement of visual acuity of the right eye 1 year ago. Magnetic resonance (MR) imaging revealed a tuberculum sellae meningioma (Fig. 1). The tumor was enhanced with homogeneous intensity after administration of a contrast material. After a year, she experienced complete loss of visual acuity of the right eye without light sense. Her visual acuity on the left side also began to decrease to 0.4 and the visual field reduced severely. At this point, we undertook surgery.

The tumor was removed through a right pterional approach. The subfrontal route was mainly used to resect the tumor. After retraction of the right frontal lobe, both the tumor and the superiorly displaced right optic nerve trunks penetrated by the tumor were exposed. However, we could not recognize the penetrated optic nerve for a while. It appeared as parts of the tumor because the tumor lay in the middle of the penetrated optic nerve and the two penetrated trunks were thin (Fig. 2A). The tumor was attached to the tuberculum sellae, which was considered as the site of origin confirming the diagnosis of a meningioma originated from the tuberculum sellae. The tumor was dissected from the adjacent cortices and nerves by maintaining arachnoid planes. The whole course of the nerve could be visualized with the removal of most of the tumor.

To confirm the penetration, the operator biopsied the bulged tumor (black arrow, Fig. 2A) penetrating the optic nerve. The tumor around the optic nerve was resected gross totally without tumor enhancements in postoperative MRIs (Fig. 3). The remaining preserved optic nerve had a penetration after tumor resection (black arrow, Fig. 2B). Pathological examination revealed the absence of neural tissue in the bulging tumor between the nerve trunks. No neural or glial tissue was found in the biopsy sample, and the pathologies of the main tumor mass and the bulging tumor were identical-grade I meningothelial meningioma with a Ki-67 index of 2%. Postoperative course was uneventful and blindness in the right eye was unchanged. However, visual acuity of the left eye improved slightly to 0.6 and its visual field improved within 1 month post-operation (Fig. 4). No additional events or symptom aggravation were noted at the 1-year follow up.

To our knowledge, penetrated optic nerves have been reported in about 10 cases of aneurysms123489101617). Thus, their incidence seems rare. Optic nerve penetrations by meningiomas or other tumors are rarer, with only 3 cases reported in 2 studies514). The cause of penetration of the optic nerve was probably tumor invasion in those cases. In the present case, our patient was operated later than that previously reported. Therefore, optic nerve penetrations in this patient could be a rare and late finding of a progressed tuberculum sellae meningioma where the growing mass might have intruded into the slit of the optic nerve514). In general, optic nerve penetration by a tumor is thought to be very rare because optic nerve compression becomes symptomatic early in the course of the tumor, which is usually operated much before the actual penetration. However, there are cases reported wherein the tumor penetration resulted in remnant visual acuity; in such cases, a congenital or de novo splitting of the optic nerve has been suggested56).

In the patient reported here, the right eye was already blind suggesting severe optic nerve damage; therefore, preservation of the right optic nerve was less important. However, patients in the previous two reports with penetration of the optic nerves by tumors had remnant visual function. Therefore, preservation of the penetrated optic nerve was justified in those cases5). In cases of a flattened oculomotor nerve severely adhered to a meningioma similar to that seen in our patient, even a meticulous and gentle dissection can damage nerve function and have unsatisfactory results. Penetration of the optic nerve is especially confusing, and can be a surgical challenge. Bulging tumors and a small split nerve make it very difficult to locate the optic nerve; this condition forces the surgeon think that he/she is dissecting around the tumors, not the other trunk of the optic nerve, thereby increasing the risk of intraoperative optic nerve damage. In one study, encasement of the internal carotid artery affected the resection grade11). Thus, penetration of the optic nerve could be a factor affecting the tumor-resection grade especially when vision is still functional. In addition, involvement of the meningioma was a factor related to post-surgical visual acuity decrement11). Optic nerve penetration may also be a poor prognostic factor of visual acuity. We discussed treatment plans according to the remnant visual acuity and dissection plane between the tumor and optic nerve.

Preserving an optic nerve may be more difficult in the case of penetration. Although optic nerve penetration by a tumor is rare, such cases help us reconsider the best surgical strategy for tumor removal in relation to the optic nerve and visual function.