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The common etiologies of pneumocephalus, presence of air in the intracranial cavity, are trauma and cranial surgery. Pneumocephalus after spinal surgery is an unusual postoperative complication. We report the case of a male 59-year-old man who developed a pneumacephalus after posterior lumbar surgery for spinal stenosis. Intraoperatively, a cerebrospinal fluid leak following a dural tear was noted and immediately repaired. The next day, the patient complained of headache and dizziness. Head and lumbar computed tomography scans revealed significant air in the frontal region, several cisterns, intraventricle, and extra-dural area in the spine canal. Symptoms were spontaneously resolved within 2 weeks with conservative management.
Pneumocephalus is defined as the presence of intracranial gas1). It usually occurs when fractures of temporal bone air cells or paranasal sinuses tear the adjacent dura6,8). Other rare causes of pneumocephalus include traumatic or iatrogenic spinal dura tear11,13,16,17). Due to recent advances in instrumentation of spinal surgery, dural tears are inevitable and surgeons are faced with increasing numbers of cerebrospinal fluid (CSF) leaks. Tears in the dural sac and CSF leakage during post spinal surgery may lead to post-operative complications, such as meningitis, arachnoiditis, epidural abscess, delay of wound healing, dural-cutaneous fistula, and pneumocephalus4). We report a case of symptomatic pneumocephalus after lumbar spinal surgery. With this case report and brief literature review, we hope to make spinal surgeons more aware of pneumocephalus as a potential cause of headache and dizziness following spinal operation.
A 59-year-old man presented with a tingling sensation and pain in both lower extremities of 6-months' duration. At admission, he complained of slight motor weakness of right foot. There was no significant medical history of or any recent history of trauma. Neurological examination revealed decreased motor strength in ankle dorsiflexion (4/5) on the right. Paresthesia and hypesthesia were present in both the L5 and S1 dermatomes. Both ankle reflexes were diminished and gait was unsteady due to pain and weakness in the leg. Neurologic claudication was precipitated by walking about 50 meters and relieved by a change in posture to squatting or to sitting. The patient denied any bowel or bladder dysfunction. Magnetic resonance (MR) imaging demonstrated severe spinal canal narrowing caused by hypertrophy of the facets and the ligament flavum with central protrusion of the disc at the L4-5 and L5-S1 levels. Unsuccessful nonoperative treatments at a regional hospital for 2-months led him to the decision to undergo surgery.
The dissection and retraction of paraspinal muscles were completed by a posterior midline approach. The following procedures were performed : an L-4 subtotal laminectomy, an L-5 total laminectomy, and a pedicle screw fixation. During the procedures, the incidental finding of a durotomy at the shoulder of the right L5 nerve root was discovered and repaired with fine silk sutures and fibrin glue, taking only a few minutes of time. A valsalve test was performed to confirm that there was no leak of the CSF. In addition, a rod insertion and posterolateral fusion were performed.
On the first postoperative day, the patient began to complain of headache and dizziness. There was no CSF leakage from the wound. The following conservative management as applied : medication, injection and hydration. On the second postoperative day, the patient demonstrated psychological depression resulting from a progressive headache. Head computed tomography (CT) scan was performed and it revealed diffuse pneumocephalus involving, both sylvian and basal cisterns, frontal subdural area, and frontal horn of the lateral ventricle (Fig. 1). The spine CT scan, which was performed due to the possibility of dural injury related to misplacement of a screw, showed a small amount of extradural air without misplacement of the instruments (Fig. 2). The patient was managed conservatively with bed rest, hydration, and close monitoring. His symptoms were gradually improved and he was discharged with no neurological deficits after 2 weeks. Plain radiograph obtained 10 days after surgery showed that the placement screws were in good positions (Fig. 3). Due to his complete clinical recovery, a follow up CT was not performed.
The term "pneumocephalus" is described as the presence of air in the intracranial cavity13). The air can be localized in subdural, subarachnoid, epidural, intraventricular, and intraparenchymal spaces7,13,14). The most frequent cause of pneumocephalus is trauma, especially fracture at the base of the skull6,8). Other intracranial causes of pneumocephalus include tumors, infections (meningitis and abscess), CSF fistula, N2O anesthesia, and cranial surgery5,7,8,14,18). Spinal causes of pneumocephalus include spinal trauma, tumor, infection, spinal procedures, and dural injury during spinal operation1,3,10,11,13,16,17). In review of the literature, there were 2 reports of symptomatic pneumocephalus secondary to iatrogenic dura tear and CSF leakage during spinal surgery13,16). One was a case of lumbar disc herniation with symptomatic tension pneumocephalus, due to iatrogenic CSF leak following surgical intervention and drainage with a vacuum suction device16). The other was a case of dural injury related to misplacement of a screw for treatment of thoracolumbar scoliosis13).
Signs and symptoms of pneumocephalus are often vague and nonspecific. A patient may complain of a headache, nausea and vomiting, dizziness, lethargy, an altered state of consciousness, and the triad of meningism12). These nonspecific symptoms can be misleading and are often considered to be insignificant following general anesthesia, as we did in this case. Pneumocephalus is diagnosed using simple X-ray, head CT scan, and MR imaging6). However, the diagnosis of pneumocephalus is not high on the diagnostic list when there is only a small amount of air. CT scan is a highly sensitive and specific diagnostic tool and is cost-effective in the diagnosis of this condition12). CT scan can detect even 0.5 cc of air in the intracranial compartment12).
In this case, head CT scan showed a small amount of air in the frontal horn of the left lateral ventricle. It is noteworthy that air can enter the 4th ventricle via the foramens of Magendie and Lushcha, even though these are small openings and the subarachnoid space round being larger.
The pathogenesis of pneumocephalus have been suggested as the following 4 hypotheses2,6,9,14,15). First, it is the inverted bottle mechanism that promotes the hypothesis that continuous leakage of CSF causes negative intracranial pressure within subarachnoid space and negative pressure substitutes air for lost CSF. This substitution ends by balancing the pressure difference. Second is the ball valve mechanism. That is, air enters the intracranial cavity through a defect whenever extracranial pressure exceeds intracranial pressure (e.g., from the paranasal sinuses during coughing, sneezing, swallowing). Third, a role is played by nitrous oxide (N2O) anesthesia. Although completely restricted to the intraoperative period, N2O will diffuse into an air-filled cavity 34-times faster than nitrogen diffuses out. Thus, the volume and pressure of the contained pneumatocele rapidly increases (mimicking brain swelling). Finally, there is a gas-forming bacteria contributing to the development of pneumocephalus. The first mechanism may be applicable in our case.
To prevent pneumocephalus following unintended durotomy and CSF leakage during spinal surgery, we propose that the head should be kept in a head down position lower than the operative field and the dural sac should be soaked with irrigation saline. Moreover, it is important to maintain proper suction power during suture of the dura.
Although very rare, a symptomatic pneumocephalus after lumbar spinal surgery might be perceived as insignificant. It is the goal of these authors to bring this issue to the attention of the spinal surgeon to remember of the issue of potential pneumocephalus, especially if headache, dizziness following durotomy, and CSF leakage during the spinal operation have occurred.
The present paper was conducted by the research fund of Dankook University in 2009.