An Unusual Complication Related to Invasive Electroencephalography Monitoring: Nonhemorrhagic Subdural Fluid Collection

To the Editor: Invasive electroencephalography (EEG) monitoring using subdural electrodes is widely applied in clinical practice. Here, we report a rare complication related to this technique, nonhemorrhagic subdural fluid collection (SFC).

A 14-year-old female was admitted to Beijing Tiantan Hospital with ictal twitch and loss of consciousness. She had no other medical history. Magnetic resonance imaging (MRI) revealed a lesion in the right parietooccipital lobe. Scalp EEG failed to detect abnormal discharges in this area. To further locate the epileptic foci, subdural electrodes were placed on the surface of the parietooccipital area, the temporal lobe, and the frontal lobe. Postoperative computed tomography (CT) scan (8 h after the operation) revealed no signs of hemorrhage [Figure 1a]. However, 14 h later, the patient was found drowsy with unequal pupils and a blunt light reflex. Repetitive CT scans showed SFC in the right frontal region near the strip and signs of brain herniation [Figure 1b and c]. An emergency operation was performed. No sign of intracranial hemorrhage was found. The electrodes were removed, and the presumed lesion was resected [Figure 1d]. After the operation, her condition stabilized and was discharged 2 weeks later. She reported no seizure recurrence in the 10-month's follow-up.

Figure 1.

Postoperative computed tomography (CT) data indicating the disease evolution in this case. (a) A CT scan 9 h after the first operation; (b) A CT scan 23 h after the first operation; (c) A CT scan 28 h after the first operation, before the removement of subdural electrodes; (d) A CT scan after the second operation. Arrow heads indicate the subdural fluid collection. Arrows indicate the resection of the presumed lesion.

Invasive EEG monitoring using subdural electrodes provides reliable information of the epileptic foci.[1] Although the subdural electrode placement is not technically demanding, significant risks accompany.[2] Common complications have been discussed previously.[3] Unlike subdural hemorrhage that has been largely encountered,[4] our case is featured by nonhemorrhagic SFC near the frontal subdural electrode. The SFC usually occurs in posttraumatic patients and is mostly asymptomatic, but our case manifested much more urgent presentations. The combination of brain swelling and SFC may be the cause of the rapid aggravation of the patient's condition. However, it is unclear whether the SFC accelerated the brain swelling. An MRI scan would have been beneficial but was impossible since our strips were not MRI-compatible. In addition, neurosurgeons habitually browse through the postoperative CT for high-density hematomas, and thus some isodensity or low-density anomalies have chances to escape their eyes. The very small amount of SFC in the first CT [Figure 1a] could have been spotted if awareness of this hidden pathology existed. Our case suggested that close observation of the patient's consciousness, movement and response would be necessary after subdural electrode placement. Repetition of CT would also be significant in patients with subdural electrodes.