(PDF 192 KB)
Miranda Conn* was a 61-year-old who had suffered decreasing vision in her left eye. She had seen various ophthalmologists over the course of the year, but none of them could figure out the cause, and her vision continued to decline. Then—to her horror—she noticed similar problems in the right eye. Her ophthalmologist at the time referred her to our clinic for evaluation.
Her Medical History
Our patient is a Caucasian woman with hypertension, osteoporosis and colon cancer. We also learned that she had undergone clipping of an anterior communicating artery aneurysm two years previously.
She was being followed by neurosurgery and was undergoing routine imaging scans. She had been assured that the aneurysm was secure and unchanged. Ms. Conn was not on any medications and had no other systemic complaints.
We Get a Look
On examination, the patient’s visual acuity was 20/50 in her right eye and count fingers in her left eye. She had a left afferent pupillary defect. Using Ishihara plates, she was able to identify 11 of 11 correctly with her right eye but only the “test” plate correctly with her left eye. (The test plate can be read by patients who are color blind, and is included to identify malingerers.) Her intraocular pressures and slit-lamp examination were normal. Her dilated fundus exam was also normal except for some temporal pallor of the optic nerve heads, the left more so than the right. We ordered a Humphrey visual field test and compared it to one sent by her referring ophthalmologist from less than a year prior. The new test revealed a superotemporal quadrant defect in the right eye and complete defect on the left (Figs. 1A and 1B). This was a significant progression from the earlier study, which had demonstrated a normal field in the right eye and an inferotemporal defect in the left eye (Figs. 2A and 2B).
We Dig Further
Realizing that we needed more information to make a diagnosis, we arranged for the patient to undergo further testing, by both our service and neurosurgery. These tests included a lumbar puncture, which was normal, and an MRI/MRA, which revealed generalized optic nerve atrophy but the image was obscured by an artifact from the aneurysm clip (Fig. 3).
We also were able to obtain the original operative report from her surgery. An excerpt read, “We then placed muslin over the region of the sessile aneurysm on the left A2 branch and then placed a small piece of Gelfoam powder to secure it.”
What’s Your Diagnosis?
|WE GET A LOOK. The results of our Humphrey visual field test (Fig. 1A and 1B) showed significant progression compared with the results that had previously been reported by the referring physician (Fig. 2A and 2B).
|FURTHER IMAGING. The MRI/MRA was obscured by an artifact from the aneurysm clip, but it still revealed generalized optic nerve atrophy (Fig. 3). For several months, the patient was lost to follow-up. When we next saw her, we found that her vision had continued to deteriorate, and she now had a temporal hemifield defect in the right eye (Fig. 4).
Muslin-induced optic neuropathy is a well-described but rare disorder. Muslin is a finely woven cotton fabric that has been used since the 1970s to wrap cerebral aneurysms that are not otherwise amenable to clipping or coiling. But with the success of microsurgical techniques, such cases are less common and this material is used less frequently.
In the body, muslin results in inflammation, fibrosis and thickening of the aneurysm wall. This secures the aneurysm, but if the inflammatory response spreads to adjacent structures it can lead to complications such as endocrinopathies, headaches, seizures, pyrexia, cranial nerve deficits and visual disturbances.1
At the time of our case, a review of the literature revealed only 30 known instances of muslin-induced optic neuropathy. Interestingly, all but four of those cases were in women. The mean onset of visual deterioration after surgery is 13 months (range of one to 54 months). In approximately half of these cases, imaging revealed an actual mass—a “muslinoma,” or foreign body granuloma.2,3
The pathophysiology of muslin-induced optic neuropathy is thought to result from a triad of factors: ischemia, compression and inflammation. Blood vessels can become occluded by the inflammatory response, resulting in ischemia of the optic nerve. There can be a mass effect on the optic nerve from the muslin fibers themselves. And inflammation from the muslin can cause a local Wegener-like vasculitic process. Histopathology of the muslinoma supports this by demonstrating acute and chronic inflammatory cells along with foreign-body giant cells.2,3
Detection. Imaging with MRI is usually the most effective means of diagnosis, as CT will often miss the pathology. MRI findings include a well-defined mass with thick, irregular, peripheral enhancement indicating edema. The relative solid hypointensity of this mass distinguishes it from an abscess.2,4
Treatment. Unfortunately, there is no accepted effective treatment for this condition. Multiple therapies have been tried, including corticosteroids, immunosuppressants, antibiotics and surgical exploration with lysis of adhesions. Spontaneous recovery has been reported, but visual recovery is unpredictable. 2,3
Use of muslin in surgery. The authors of one case report recommend that use of muslin be avoided if possible. If muslin must be used, it is recommended that the patient be made aware that this material was used during their surgery and that they should have frequent eye exams and visual fields performed.1
Unfortunately, our patient was lost to follow-up for a few months. When she returned, her visual acuity had dropped to 20/60 in the right eye and hand motion in the left eye. The visual impairment in her right eye had also progressed to a temporal hemifield defect (Fig. 4). Her neurosurgeon did not feel that she was a good surgical candidate for exploration, and so she was given high-dose IV steroids with an oral steroid taper over two weeks. Since then, her vision and visual fields have progressed some, but only minimally and more slowly than before.
* Patient name is fictitious.
1 Taravati, P. et al. Surv Ophthalmol 2006;51:434–443.
2 Bhatti, M. T. et al. Am J Neuroradiol 2000;21:346–352.
3 Goldsberry, D. H. et al. J Neuroophthalmol 2004;24:42–45.
4 Yoon, M. A. et al. J Neurosurg 2010;112:640–647.
Dr. Rowland is a resident and Dr. Acierno is a neuro-ophthalmologist, a professor of clinical ophthalmology and the residency director. Both are at the Louisiana State University/Ochsner Ophthalmology Department. The authors have no financial disclosures.