Treatment of pseudotumor cerebri by primary and secondary optic nerve sheath decompression

Measurement and relationship of subarachnoid pressure of the optic nerve to intracranial pressures in fresh cadavers

We performed a study on six fresh cadavers to measure the subarachnoid pressure of the optic nerve and to determine its relationship to intracranial pressure. A lateral orbitotomy via a coronal flap was used to expose the optic nerve. Various intracranial pressures were achieved by saline infusion through a ventriculostomy. The subarachnoid pressure of the optic nerve was measured at 5 and at 25 mm posterior to the globe under conditions of the created intracranial pressure. The effectiveness of optic nerve sheath decompression performed by two standardized surgical techniques was determined experimentally and by theoretic calculations; the role of the bulbous portion of the optic nerve was assessed experimentally. Measurements of the subarachnoid pressure of the optic nerve showed interindividual variation and a linear relationship with the intracranial pressure. Surgical decompression through a 3 x 5-mm window was more effective than were three linear 5-mm incisions. The bulbous portion of the optic nerve was found to have an important role in cerebrospinal fluid circulation.

Optic nerve decompression improves hemodynamic parameters in papilledema

PURPOSE

The purpose of this study is to examine changes in color Doppler imaging parameters before and after optic nerve sheath decompression (ONSD) for chronic papilledema caused by pseudotumor cerebri (PTC).

METHODS

Color Doppler imaging was performed within 48 hours before surgery and within 48 hours after the procedure using a color Doppler unit with a 7.5-MHz phased linear transducer. Pulsed Doppler spectrum analyses were recorded digitally on videotape from the ophthalmic, central retinal, and short posterior ciliary arteries, using a 0.4 x 0.6-mm sample volume.

RESULTS

Blood flow velocities in the ophthalmic, short posterior ciliary, and central retinal arteries of 24 eyes were significantly decreased compared with a healthy age-matched group. Eyes with visual acuities worse than 20/30 before surgery had significantly decreased velocities in the ophthalmic, short posterior ciliary, and retinal arteries, whereas in eyes with visual acuities better than 20/30, only the short posterior ciliary and central retinal arteries demonstrated decreased velocities. In addition, Gosling's pulsatility index was increased for the central retinal artery but not the ophthalmic or short posterior ciliary arteries. Thirteen eyes improving in visual acuity and field after ONSD demonstrated significant improvement in all color Doppler imaging parameters for the short posterior ciliary arteries. The ophthalmic artery diastolic velocity also increased significantly but the central retinal artery parameters did not change. The eyes that remained stable or worsened did not demonstrate significant postoperative changes.

CONCLUSION

These results suggest that some of the visual loss from chronic papilledema may be due to ischemia, and worsening visual acuity correlates with greater impairment of the retrobulbar circulation. One of the mechanisms by which ONSD improves visual function may be reversal of this ischemic process.

Operative complications of optic nerve sheath decompression

BACKGROUND

Optic nerve sheath decompression (ONSD) is a procedure that is advocated for the treatment of certain types of optic nerve dysfunction associated with progressive decline in visual function. The reported postoperative complications attributed to ONSD surgery are relatively few and predominantly transient and benign. Few postoperative vascular complications are reported.

METHODS

The authors performed a retrospective review of the operative and postoperative course of 31 consecutive patients (38 eyes) undergoing ONSD surgery for various types of optic nerve dysfunction associated with progressive decline in visual acuity, visual fields, or both. The authors evaluated the reports of other investigators to ascertain the spectrum and diversity of postoperative complications associated with ONSD.

RESULTS

Fifteen (40%) of the 38 eyes undergoing ONSD had postoperative complications, including temporary motility disorders (29%) and pupillary dysfunction (11%). Additionally, four eyes (11%) had postoperative vascular complications, including two central retinal artery occlusions (CRAOs), one superotemporal branch retinal artery occlusion (BRAO), and one episode of transient outer retinal ischemia. Both eyes with postoperative CRAOs had poor visual outcome. Eyes that had undergone prior ONSD were significantly more likely to have vascular complications than those without a previous operation (Fisher's exact test, P = 0.025).

CONCLUSIONS

Optic nerve sheath decompression can be associated with a variety of postoperative complications, the majority of which are minor and resolve without sequelae. Other complications, such as a CRAO, can be associated with significant visual loss. The physician and patients should be aware of the potential risks of ONSD, including significant visual morbidity, when considering this form of treatment.

Lumboperitoneal shunting: a retrospective study in the pediatric population

There is a shortage of data concerning the long-term follow-up of patients with lumboperitoneal (LP) shunts, especially in the pediatric population. A retrospective study of 143 patients who underwent LP shunting between 1974 and 1991 was therefore performed. The mean age at the time of shunt insertion was 3.3 years (range, 18 d to 17.8 yr), and the indication for shunting was: hydrocephalus (81%), cerebrospinal fluid fistula (12%), and pseudotumor cerebri (7%). The mean follow-up time was 5.7 years (range, 5 d to 17.5 yr), and during this period, there were five deaths of which one was shunt related (2.5 yr post-shunt insertion). Of the types of LP shunt used during the study period, the T-tube shunt (101 patients) fared significantly better (P = 0.003) than the percutaneous type (42 patients), and the overall survival characteristics for the T-tube shunt approximated those seen for ventriculoperitoneal shunts, with a 50% probability of remaining free of malfunctions for 5 years. A high rate of migration (19%) was partially responsible for the poor performance of the percutaneous-type shunts. By the end of the study, 40 patients (28%) had been converted to ventricular shunts, and this rate of conversion was similar for both shunt types. LP shunts have certain advantages over other forms of cerebrospinal fluid diversion and were successfully used for various clinical conditions during this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Decompression of the optic nerve sheath for vision-threatening papilledema caused by dural sinus occlusion

Obstruction of the dural sinuses produces a clinical syndrome that resembles pseudotumor cerebri. In these patients, unremitting papilledema can cause blindness. We performed decompression of the optic nerve sheath in four patients who had occlusion of the dural sinuses. The operation achieved rapid relief of papilledema and recovery of vision. In three patients, fenestration of the nerve sheath of only one eye resulted in resolution of papilledema in both eyes. The procedure appears to relieve papilledema by filtering small quantities of cerebrospinal fluid into the orbit. It did not lower cerebrospinal fluid pressure in three patients who underwent lumbar puncture after surgery. Optic nerve sheath decompression is an effective operation for salvage of vision in patients with obstruction of the dural sinuses.