The diagnosis of idiopathic intracranial hypertension (IIH) is based on the presence of optic disc edema, elevated opening pressure on at least 1 lumbar puncture (LP), a normal cerebrospinal fluid composition, and normal MRI of the brain (1). In many cases, these features are straightforward. In some cases, however, the optic disc signs are difficult to interpret because of congenital anomaly, gliosis, or pallor. Visual field results, which depend entirely on the patient's input, may be unreliable. In these circumstances, the physician relies heavily on the opening pressure on LP as a means of determining intracranial pressure (ICP). However, LP may provide an inaccurate measure of ICP, given its known moment-to-moment fluctuations and the effects on ICP of straining, positioning, and pharmacologic sedation (2-5).
Originally reported by Lundberg (6), ICP monitoring is now commonly employed in the management of head injury, poor-grade subarachnoid hemorrhage, intracerebral hemorrhage, hydrocephalus, and craniosynostosis. Several large studies (7-11) of continuous ICP monitoring have been done to evaluate cerebrospinal fluid dynamics and elucidate possible etiologies of IIH but rarely to influence clinical management. In those few studies directed at management (3,12-15), 24-hour fluctuations in ICP ranging up to 30 cm H2O have been reported (13).
ICP monitoring has not become a part of clinical practice in managing IIH perhaps because it is perceived as not providing a sufficiently reliable measure of ICP to justify its expense and potential risks. Although an intraventricular drain connected to an external pressure transducer is still considered the gold standard for measurement of ICP, newer intraparenchymal devices are less invasive and carry minimal risk of infection or hemorrhage (5,16). Recent studies using the Codman ICP Monitoring System (Codman & Shurtleff, Inc., Raynham, MA), the device used in our institution, have shown that the drift from zero, an early concern with the new devices, is minimal and the recordings of ICP are as accurate as intraventricular monitoring (16,17).
We present 10 cases of suspected IIH in which ICP monitoring played a pivotal role in diagnosis and management.
We undertook a chart review of all patients who had undergone ICP monitoring in the management of IIH between 2001 and 2008 at the University of Michigan. Patients were excluded if follow-up information was not available for at least 1 year after monitoring. The diagnosis of IIH was based on ophthalmic manifestations, elevated opening pressure on at least 1 LP, a normal cerebrospinal fluid composition, and normal brain MRI (18). In all cases in which LP was performed at our institution, the patient was placed in the lateral decubitus position prior to measuring the opening pressure. All patients were examined in the University of Michigan Neuro-Ophthalmology clinics.
ICP was monitored continuously for at least 24 hours using the Codman ICP Monitoring System, an intraparenchymal pressure monitor. The procedure was performed at the bedside in the neurointensive care unit according to the following standard protocol. None of our patients experienced any complications or had any complaints about the process.
The patient was placed in the supine position, and a small patch of hair was shaved 3 cm paramedially and 3 cm anterior to the coronal suture in the plane of the midpupillary line. The patient was given 7 mg of midazolam and 4 mg of morphine sulfate intravenously for sedation and analgesia. A local anesthetic was administered into the skin, and a 2-cm linear incision was carried down to the skull. A 4-mm-diameter Codman twist drill was used to create a burr hole. The dura was perforated with the tip of an 18-gauge spinal needle. A tunneling catheter was inserted from the burr hole. The ICP monitor catheter was then placed through this tunneling device, which was then removed. The distal tip of the catheter containing the transducer was placed in the exposed cortex at a depth of 1 cm. The pressure sensor was connected to a bedside monitor through a fiber optic cable. After a triphasic waveform representing the ICP (with respiratory and cardiovascular variability) appeared on the monitor, the wound was closed with a running 3-0 nylon suture. The fiber optic cable was sutured to the scalp. The procedure required about 30 minutes (4).
Ten patients formed the basis of this study, including 7 women and 3 men. Average age was 24 years (range, 7-49 years). ICP monitoring led to cessation of medical treatment for IIH in 5 patients and removal of a lumboperitoneal shunt in 1 patient. In 2 individuals (Cases 8 and 9), the clinical examination and ICP monitoring excluded the diagnosis of IIH and therapy was begun for migraine. In 2 patients (Cases 4 and 10), ICP monitoring confirmed persistent elevation of ICP and both underwent surgery with placement of a ventriculoperitoneal (VP) shunt. Clinical data are shown in Table 1. Individual case summaries and illustrations are available online at Supplemental Digital Content 1 (see Case Reports, https://links.lww.com/WNO/A17).
Our 10 patients with suspected or proven IIH were all at a juncture where more invasive treatment options (shunt placement or revision) were considerations. In 8 cases, LP had shown elevated opening pressures. In 7 of them, ICP monitoring failed to confirm high ICP. In those 7 cases, we were able to avoid unnecessary invasive surgical options. In 1 patient (Case 4), ICP monitoring confirmed high ICP suggested by LP, justifying placement of a VP shunt. In 2 patients (Cases 8 and 10), LP was not performed. In one of those patients (Case 8), ICP monitoring was normal, so shunt revision was not necessary; in the other patient (Case 10), ICP monitoring showed a high ICP, so a VP shunt was placed.
An accurate measure of ICP was critical in guiding our management because many patients had confusing clinical manifestations. Optic discs had congenital anomalies (Cases 1, 6, and 9), gliosis (Case 5), or pallor (Cases 2, 3, 8, and 10). One patient had normal-appearing optic discs but a history of multiple elevated LP opening pressures (Case 7), raising the concern for IIH without papilledema. In many patients, visual function testing was unhelpful because of prior large visual field defects or inconsistent results on multiple testing sessions.
LP has long been known to provide an imperfect measure of ICP because of difficulties and errors in patient positioning, manometric technique, leakage around the needle (19), and inherent fluctuations in ICP. Based on monitoring, it is known that ICP generally measures between 5 and 10 mm Hg above atmospheric pressure (2), but during a 12-hour period, it may fluctuate within a range of 300 mm H2O (13). Such fluctuations, together with the inaccuracies of LP opening pressures, have prompted the use of ICP monitoring.
Although there has been experience with ICP monitoring in cases of traumatic brain injury, hydrocephalus, craniosynostosis, and acute disseminated encephalomyelitis, there has been less experience in IIH (3,12-15). Johnston and Paterson (3) performed intraventricular ICP monitoring in 21 suspected IIH patients and found that 5 patients never had elevated ICP. They emphasized the value of ICP monitoring in minimizing false-positive diagnoses of IIH.
Cooper et al (12) implanted a Hittman-Meyer radioisotope-activated subdural pressure sensor device for long-term (up to 14 months) monitoring of 8 patients with IIH. LP and sensor pressures, recorded simultaneously but independently by 2 observers, were highly correlated. They detected fluctuations in ICP of 200 mm H2O from one day to the next, but the impact of these findings on clinical management was not described. Gucer and Viernstein (13) inserted an extradural device in 4 IIH patients for up to 10 months and monitored for epochs extending up to a week. They demonstrated wide spontaneous fluctuations in ICP and a sustained reduction following treatment with acetazolamide or corticosteroids. A drawback of their system was a drift in the baseline pressure and the need for LP calibration. Shunt infection led to removal in 1 case. Spence et al (14) utilized cerebrospinal fluid pressure monitoring via lumbar catheter in 7 of their 9 patients to establish a diagnosis of elevated ICP. The patients had normal ophthalmoscopic examinations, but clinical histories were suspicious for IIH.
For ICP monitoring to be valuable in the management of complicated IIH cases, one must prove that it is procedurally uncomplicated, safe, painless, and more accurate than LP (20). Among the currently available ICP monitoring devices, intraventricular monitors with external transducers are considered the gold standard as compared to the subarachnoid-subdural-extradural monitors so often used in the past (12-15). The subarachnoid screw or bolt is less accurate than the intraventricular catheter, especially at higher pressures, owing to plugging of the device with brain tissue (2).
Gopinath et al (17) demonstrated that a miniature strain-gauge transducer, the one used in the Codman ICP Monitoring System, is highly accurate and stable and that it is a reliable alternative to pressure monitoring through a ventricular catheter. The advantages include small size (1.2 mm) and a flexible cable that allows the transducer to be tunneled in order to minimize infection. Because it is placed in the brain parenchyma rather than into a cavity, it does not become plugged (17). Furthermore, it is safer than the intraventricular catheter because it need not be inserted into a small ventricle deep beneath the surface. The Codman ICP Monitoring System employed in our patients has an accurate transducer (21) and is widely used by neurosurgeons to monitor ICP in intensive care units (22). None of our patients experienced any complications or had any complaints about the process.
Now that an appropriate ICP-measuring device is available, we propose that short-term continuous ICP monitoring be considered more readily in the management of IIH cases when clinical signs are confusing and an invasive option is under consideration.
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