Commentary

The authors present an interesting case and an important reminder that while imaging studies have substantially improved our ability to make a diagnosis, they are no substitute for pathological analysis. As CT and MRI have improved, neurosurgeons have been more reluctant to obtain tissue material surgically in lesions considered better treated by other modalities. This reluctance is true for the treatment of optic nerve sheath meningiomas, for which recent studies have indicated that the results associated with fractionated radiation therapy are far better than those associated with observation, surgery, or surgery combined with radiation therapy.[1] Thus, it is often advocated that patients with lesions that look like optic nerve sheath meningiomas be treated without pathologic confirmation.

It is well recognized that other pathologic processes can produce a radiographic appearance similar to that of an optic nerve sheath meningioma. These entities most importantly include sarcoid lesions and infiltration related to lymphoproliferative disorders, such as lymphoma or leukemia. In addition, idiopathic orbital inflammatory disease may affect primarily the optic nerve sheath. There are often specific clues to exclude these unusual lesions, including the almost universal presence of pain in patients with orbital inflammatory disease. Another clue is evidence of additional systemic involvement, as often found in sarcoid or lymphoproliferative disorders. Radiographically, breast carcinoma also may be indistinguishable from meningioma.[2]

It is important to recognize that this patient did not have a typical optic nerve sheath meningioma.[3] Although the optic nerve sheath may be involved secondarily from meningiomas originating in the anterior clinoid or tuberculum sella regions, primary optic nerve sheath meningiomas arise within the orbit itself. The conclusions of Turbin and coworkers[1] were based on a limited series of patients that excluded all with primary involvement of the clinoid or tuberculum. In this patient's case, the lesion had several atypical features. The lesion not only involved the superior portion of the canal and the intercanalicular optic nerve, but the patient had a clinical history of rapidly deteriorating vision. Although meningiomas can worsen suddenly, most have an exceptionally slow course. In particular, primary optic nerve sheath meningiomas can be unrecognized for years or thought to represent such chronic diseases as optic neuritis.

The final key piece of atypical information in this case was the patient's history of breast carcinoma. Breast carcinoma metastatic to the area of the optic canal is unusual but occurs. This patient's history is similar to that of patients with known prostrate carcinoma[4] and remains a red flag for additional evaluation.

In the discussion, the authors note an additional problem: identifying different locations for involvement of the visual system. Metastatic lesions to the optic nerve head, optic nerve sheath, and intracranial portion of the optic nerve all decrease visual acuity, but their incidence is definitely different. The authors quote Ferry and Font,[5] who studied metastatic tumors to the globe. None of their patients had tumors that were metastatic to the optic nerve. However, Ferry and Font's series was generated from an ophthalmic pathology study that only considered the globes and anterior orbit. Therefore, although we have good data on metastatic tumors to the choroid and proximal nerve, good data regarding metastasis to the optic canal are lacking.

The authors correctly note that involvement of the optic nerve within the globe by metastatic tumor is unusual.[6] [7] [8] However, choroidal involvement of metastatic breast carcinoma and other metastatic disease is not all that rare. Pathologically, metastatic disease is the most common neoplastic process found in the eye. Its incidence is slightly higher than that of the most common primary tumor of the choroid, melanoma. Many of these tumors, however, are asymptomatic and found only at autopsy. Breast carcinoma can metastasize to the optic nerve sheath but not involve the canal or tuberculum sella. A patient with a tumor involving the optic nerve sheath was reported from Emory in 1996[9] and a second patient was seen in Australia in 1998.[10] These patients showed characteristics similar to the patient in this study, rapidly developing complete loss of vision as opposed to the course expected for an optic nerve sheath meningioma.

I agree with the authors' contention that a metastatic lesion must be considered in a patient with a previous history of breast carcinoma and a lesion of the orbital apex involving the area of tuberculum sella and anterior clinoid. This case also points out the importance of not relying strictly on imaging studies. The patient's clinical history, medical history, and atypical findings may provide clues that suggest the need for additional diagnostic tests.

REFERENCES

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• 2 Mafee M F, Goodwin J, Dorodi S. Optic sheath meningiomas. Role of MR imaging.  Radiol Clin North Am. 1999;  37 37-58
• 3 Newman S A. Optic nerve sheath meningiomas.  Techniques in Neurosurgery. 2003;  9 64-77
• 4 Kattah J C, Chrousos G C, Roberts J, Kolsky M, Zimmerman L, Manz H. Metastatic prostate cancer to the optic canal.  Ophthalmology. 1993;  100 1711-1715
• 5 Ferry A P, Font R L. Carcinoma metastatic to the eye and orbit: a clinicopathological study of 227 cases.  Arch Ophthalmol. 1974;  92 276-286
• 6 Mili Boussen I, Kamoun R, Boussen H et al.. Metastatic neoplasia in the optic nerve [in French].  Rev Neurol. 2004;  160 1071-1074
• 7 Shields J A, Shields C L, Singh A D. Metastatic neoplasms in the optic disc: the 1999 Bjerrum Lecture. Part 2.  Arch Ophthalmol. 2000;  118 217-224
• 8 Arnold A C, Hepler R S, Foos R Y. Isolated metastasis to the optic nerve.  Surv Ophthalmol. 1981;  26 75-83
• 9 Newman N J, Grossniklaus H E, Wojno T H. Breast carcinoma metastatic to the optic nerve.  Arch Ophthalmol. 1996;  114 102-103
• 10 Backhouse O, Simmons I, Frank A, Cassels-Brown A. Optic nerve breast metastasis mimicking meningioma.  Aust N Z J Ophthalmol. 1998;  26 247-249