Indwelling spinal epidural catheters offer a generally safe and effective method of providing continuous intraoperative and postoperative analgesia. But considerable skill is involved in proper placement of the catheter. Even in skilled hands, accidental dural puncture may occur, estimated at a frequency of 0.19%–3.6% (1–4).
The most common enduring complication of accidental dural puncture is “postdural puncture headache” (PDPH), reliably distinguished from other headache only by being more intense upon sitting or standing. Its incidence after dural puncture is estimated at 50%–80% (5,6), and higher when cutting or larger gauge needles are used (7). PDPH is attributed to intracranial hypotension (IH) owing to leakage of cerebrospinal fluid through the dural hole. Because the epidural needles are usually 18-gauge, wider than the 22-gauge needles recommended for lumbar puncture (7), PDPH is likely to be more common after accidental dural puncture than after lumbar puncture.
Brain imaging often displays one or more of the following signs of IH: subdural fluid collection, dural thickening and excessive contrast enhancement, engorged dural venous sinuses or change in sinus configuration, pituitary gland enlargement, and downward displacement of the brainstem (8–16).
The most common neurologic sign associated with PDPH is diplopia, usually caused by sixth nerve palsy, and estimated to occur in no more than 0.25% of dural punctures. The palsy is attributed to tension on the nerve as the brainstem sinks in IH (17). Because epidural pain control systems are used so commonly and IH is relatively rare in this setting, clinicians are apt to overlook IH as the cause of postoperative diplopia, particularly if the ophthalmologic findings are subtle or appear well after the epidural pain catheter has been removed, or if the patient fails to report the postural nature of the headache. If radiologists are not alerted that IH is a consideration, they may not look for its imaging features or incorrectly attribute these features to inflammation.
We describe 6 cases of sixth nerve palsy following presumed dural puncture in epidural pain control systems to highlight confounding features in the diagnosis of IH in this setting. Recognizing these confounders, clinicians and radiologists should be able to reject alternative diagnoses and avoid diagnostic lumbar puncture, which could exacerbate the condition.
The January 2006 to December 2011 records of the Neuro-Ophthalmology and Ophthalmology Inpatient Consultation Services of the University of Michigan Medical System were searched for patients who had been diagnosed with sixth nerve palsy ultimately attributed to IH associated with an epidural pain control system. At least one characteristic magnetic resonance imaging (MRI) feature of IH had to be present.
Six patients met entry criteria and are the basis of this report. For the purposes of this study, their brain MRIs were re-reviewed by a single neuroradiologist (J.W.), who graded the presence of 4 brain imaging signs of IH: subdural fluid collection, excessively enhancing and thickened pachymeninges, enlarged pituitary gland, and downward displacement of the brainstem (9–16). Each sign was assigned a grade, as follows: 0 = absent, 1 = mild, and 2 = marked. We elected not to include measurement of the size of the dural sinuses because of great normal variability. Investigational review board permission was granted.
A 22-year-old man with refractory inflammatory bowel disease reported binocular horizontal diplopia but no headache 9 days after undergoing subtotal colectomy and ileostomy followed by gastrojejunostomy tube placement. Postoperatively, he received an epidural bupivacaine infusion catheter for pain management that was removed 4 days later. He had been treated chronically with prednisone and tacrolimus (Table 1).
He had no other relevant medical history and denied other neuro-ophthalmologic symptoms. Bedside examination disclosed normal visual function. The ocular adnexal examination was normal, but the conjunctiva was hyperemic in both eyes without discharge. There was mild limitation of abduction of the right eye with a slightly incomitant esodeviation. Other aspects of the neuro-ophthalmologic examination were normal.
In the setting of inflammatory bowel disease, the ophthalmologic findings raised a suspicion of orbital inflammatory disease. Brain and orbit MRI showed grade 2 pachymeningeal enhancement and thickening but no other signs of IH (Fig. 1). Because the interpreting neuroradiologist was not informed that an epidural pain catheter had previously been in place, the possibility of an inflammatory or neoplastic cause of the meningeal findings was considered. Following an unsuccessful bedside lumbar puncture, a fluoroscopically guided lumbar puncture yielded fluid at such a slow rate that an opening pressure could not be measured. The cerebrospinal constituents were normal.
Corticosteroid eyedrops were administered for presumed conjunctival inflammation. Within 2 weeks, the diplopia resolved and headache subsided within the next few weeks. Over the next 2 years, no new systemic or neuro-ophthalmologic abnormalities developed.
A 38-year-old woman reported binocular horizontal diplopia 6 days after undergoing open biliary cystectomy and cholecystectomy for a recently diagnosed liver cyst. She also described postoperative headache and neck stiffness. As she was bed confined, she could not report whether the headache was postural. A pain management epidural catheter placed immediately after surgery was removed on the fifth postoperative day, and one day later she reported diplopia. In addition, the patient experienced night sweats and a 15-lb weight loss over the previous 6 months (Table 1).
Visual acuity and confrontation visual fields were normal, as were pupil size and reactivity. The left eye had limited abduction while other ductions were normal. The patient had a 20 prism-diopter esotropia in primary gaze, increasing to 30 prism diopters in left gaze and decreasing to 14 prism-diopters in right gaze. All other aspects of the neuro-ophthalmologic examination were normal.
Brain MRI showed grade 1 pachymeningeal enhancement and grade 1 pituitary enlargement (Fig. 2). Grade 1 bilateral subdural fluid collections, overlooked initially, were detected on later review. In view of the reported weight loss and night sweats, the radiologist could not exclude infectious or neoplastic meningitis as the cause of the MRI findings.
Before lumbar puncture, as the patient became ambulatory, she reported that her headache was postural. With that information, clinicians thought of the epidural pain catheter, presumptively diagnosed IH, and canceled the lumbar puncture.
Two weeks later, her headache resolved, but the left abduction deficit was still present. Five weeks later, the deficit had improved, but she still had esotropia in primary and left gaze.
A 21-year-old woman received epidural analgesia for parturition. On the first postpartum day, she developed a severe headache, seizures, and depressed consciousness (Table 1).
Brain computed tomography (CT) revealed a large right subdural hematoma with midline shift requiring emergent craniotomy. Several weeks later, she reported having binocular horizontal diplopia of an uncertain duration. All aspects of the neuro-ophthalmologic examination were normal except for a 14 prism-diopters esotropia in left gaze, consistent with a left sixth nerve palsy. Brain MRI showed grade 1 pachymeningeal enhancement and thickening, grade 2 pituitary gland enlargement, and grade 2 downward displacement of the brainstem consistent with IH (Fig. 3). The patient underwent epidural blood patching and the ocular motor findings gradually resolved.
A 36-year-old man presented with horizontal binocular diplopia. Fourteen months earlier, he had undergone excision of a malignant melanoma on his upper back. Right axillary lymph node dissection was positive (Table 1).
One year later he developed low back, left hip, anterior thigh, and knee pain. Brain MRI was normal, but MRI of the spine showed T1, T5, L2, and L5 vertebral body lesions suggestive of metastatic melanoma. He underwent L2 partial vertebrectomy, removal of an intraspinal mass, confirmed pathologically as melanoma, and L1-L3 posterior segmental fusion.
On the 10th postoperative day, he reported new binocular horizontal diplopia worse on left gaze and associated with headache exacerbated by sitting up. Neuro-ophthalmological examination was normal apart from mild limitation of abduction of the left eye. He had 6 prism-diopters of esophoria in the primary gaze position, increasing to 18 prism-diopters of esotropia on left gaze and 4 prism-diopters of esophoria on right gaze.
Brain MRI showed grade 2 pachymeningeal enhancement and thickening and grade 2 downward displacement of the brainstem (See Supplemental Digital Content, Figure 1, http://links.lww.com/WNO/A53). Given his history, these findings were interpreted as suggestive of meningeal spread of melanoma. Lumbar puncture yielded no cerebrospinal fluid but fluid was obtained with cervical puncture and had normal constituents. Chest, abdomen, and pelvis CT showed no metastatic lesions.
After these studies had been performed, it became apparent that a Jackson-Pratt drain had been left in the epidural space for 4 days postoperatively. Brain MRI findings were now reinterpreted as consistent with IH. One month later, the patient's headache and neuro-ophthalmologic findings had resolved.
A 71-year-old woman reported the sudden onset of horizontal binocular diplopia on the 14th day following bilateral reduction pneumoplasty for severe emphysema. An epidural pain-control catheter had been in place since the surgery. The patient denied headache, although she had been largely bed-confined. There were no other pertinent symptoms (Table 1).
Bedside neuro-ophthalmic examination disclosed an alert patient with no abnormalities apart from ocular motility and alignment. Ductions were full, but abducting saccades were slower than adducting saccades in both eyes. She described slightly wider separation of diplopic images on side gaze than in primary gaze, that appeared equal in right gaze and left gaze. Measurement of alignment indicated 8 prism-diopters of esotropia in primary gaze position and slightly greater esodeviation in right and left gaze. These findings were attributed to a break in fusion because of narcotic medication.
Brain MRI showed grade 1 pachymeningeal enhancement but no other findings to suggest IH (See Supplemental Digital Content, Figure 2, http://links.lww.com/WNO/A53). A full spine MRI failed to disclose a cerebrospinal fluid leak. Lumbar puncture yielded normal spinal fluid but an opening pressure was not obtained owing to difficulty positioning the patient without causing discomfort. The epidural catheter was eventually removed. Follow-up examination 2 months later was normal.
A 35-year-old woman with Crohn disease underwent ileocecal revision with placement of a mid-thoracic epidural catheter for pain control. On the first postoperative day, she complained of severe headache exacerbated by sitting up. An epidural catheter was removed on the second postoperative day, but the headache worsened and she developed neck discomfort, nausea, and vomiting. She was treated with narcotic analgesics. On the sixth postoperative day, she complained of intermittent diplopia (Table 1).
Bedside examination disclosed normal visual acuity and confrontation visual fields, pupils, and funduscopy. She had full ocular ductions, but when fixating on a distant target, she noted diplopia in extremes of lateral gaze. On cover testing, the patient was orthotropic in primary position with 15 prism-diopters of esotropia in right and left gaze.
The patient reported worsening headache with pain extending down her back, together with chills, raising concern for spinal epidural hematoma or abscess. Brain MRI showed grade 2 pachymeningeal enhancement and thickening, grade 2 enlargement of the pituitary gland, and grade 1 downward displacement of the brainstem (See Supplemental Digital Content, Figure 3, http://links.lww.com/WNO/A53). Spine MRI showed an extrathecal fluid collection thought to represent a leak. Neurological examination disclosed no evidence of spinal cord or root compression. On the ninth postoperative day, she underwent a lumbar blood patch procedure. The following day, headache resolved but diplopia persisted.
Two weeks after surgery, the patient had full ocular ductions, with an 18 prism-diopter esotropia in primary and left gaze that increased to 25 prism-diopters on right gaze. Two months after the surgery, the diplopia had disappeared and ocular alignment was normal.
These 6 patients reported diplopia days to weeks after implantation of a spinal epidural catheter for postprocedural pain control (Cases 1, 2, 5, 6), postoperative fluid evacuation (Case 4), or following parturition (Case 3).
Usually attributed to sixth nerve palsy, diplopia has been amply documented in IH (17–23). This report is distinctive in pointing out the confounding clinical features that delayed diagnosis for the following reasons:
- Clinicians often did not realize that an epidural catheter had been in place. In some cases, the catheter had long been removed when the diplopia was first reported. When it was still in place, it often was not considered. Case 4 had a Jackson-Pratt epidural drain left in place postoperatively, a device about which clinicians caring for the patient were unfamiliar.
- The diplopia was not reported immediately after the procedure. The delay ranged from 5 to 14 days, such that clinicians did not consider it a consequence of the procedure. In a comprehensive review of 95 cases of IH-associated sixth nerve palsy, the palsy was found to develop between 1 and 21 days after dural puncture, usually between 4 and 10 days (17).
- The ocular motor findings were not obvious. The examination was usually at the bedside. Because they were uncomfortable as they were recovering from their procedures, patients could not always cooperate adequately with ocular motility and alignment testing. Ductional deficits were usually mild. In 2 patients (Cases 5, 6), bedside measurements suggested comitant esotropia attributable to a break in fusion, a common occurrence in postoperative patients treated with pain-relieving medications. But the comitant misalignment often persisted after the patients were on very low doses of narcotics that did not alter consciousness and would not have been expected to disrupt fusion. Accordingly, we believe that IH should be considered a cause, not merely of sixth nerve palsy, but also of comitant esodeviation with normal or near-normal ocular ductions.
- A history of postural headache, so characteristic of IH, could not always be elicited. Some patients had no headache, perhaps because they were receiving pain medication. Others were not ambulatory and were unable to report a postural component of their headache. In IH-associated sixth cranial nerve palsy, headache may precede the palsy, follow it, or not occur at all (17).
- There were clinical features that suggested a cause other than IH. Case 1 had a history of inflammatory bowel disease and displayed conjunctival hyperemia, prompting consideration of an orbital process. Case 2 had weight loss and night sweats, leaving open the possibility of inflammatory or neoplastic meningitis. Case 3 had undergone evacuation of a subdural hematoma. Case 4 had metastatic melanoma.
- Radiologists did not exclude a diagnosis of pachymeningitis. All 6 patients had diffuse pachymeningeal enhancement, the most common neuroimaging abnormality in IH (24), a sign attributed to dural vascular engorgement. Although a diffuse rather than a nodular pattern of pachymeningeal enhancement is thought to favor IH over inflammatory or neoplastic pachymeningitis, the distinction is imperfect, especially when the patient has clinical features that could be consistent with serious medical conditions (Cases 1, 2, 4) (25). Three patients (Cases 3, 4, 6) had signs of downward displacement of the brainstem, which should be definitive for IH, but the findings were subtle. Three patients had pituitary gland enlargement (Cases 2, 3, 6), a sign that, by itself, is not diagnostic of IH. One patient (Case 2) had subdural fluid collections, which, together with diffuse pachymeningeal enhancement, would strongly suggest IH. However, the collections were small and initially overlooked. Because the interpreting radiologists were unaware that an epidural pain catheter had been used, they were obligated to consider inflammatory or neoplastic causes of these imaging signs.
Postdural puncture headache and diplopia are attributed to traction at the cranial base owing to downward displacement of the brainstem (17). PDPH usually subsides spontaneously within 1 week but can take up to 6 months (7,26,27). Epidural blood patch at the site of puncture, the preferred treatment for PDPH, is administered within 48 hours if the postural headache is not resolving. It was only performed in 2 of our patients (Cases 3, 6).
Intracranial hypotension–associated diplopia is nearly always caused by sixth nerve palsy, believed to arise from traction at the petroclival junction, where the sixth cranial nerve is tethered in Dorello canal. The palsy is usually unilateral (80%) (17,20,21,23). Patients range in age from 17 to 69 years and men and women are affected equally. Spontaneous recovery occurs in 90% of patients within 8 months, the majority recovering fully within 3 months. If the palsy is present after 8 months, it will be permanent (17). Epidural blood patch, effective in relieving PDPH, does not alter the recovery of sixth nerve palsy (17).
The consequences of not recognizing the connection between diplopia and IH are a fruitless and perhaps harmful diagnostic work-up that includes lumbar puncture, which in 2 of our patients (Cases 1, 5) led to “dry taps” and in 1 case (Case 4) to an unnecessary and risky cisternal puncture. In the experience of one of the authors (J.D.T.), repeated lumbar puncture in a patient with IH-associated diplopia may convert a partial into a total sixth nerve palsy without recovery. If an epidural pain control system has been used and one or more of the neuroimaging features of IH is present, a presumptive diagnosis of IH as the cause of diplopia can be justified without the need for lumbar puncture confirmation of low intracranial pressure.
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