Incidence

The incidence of CSF fistula is relatively rare due to the fact that a majority of dural tears heal spontaneously after a primary repair and only a small percentage of patients develop symptoms. In a multicenter study of 108,463 spine surgeries, the incidence of dural tears during the course of bone removal or during dural sac or root retraction was noted to be 1.6%. The incidence was higher for surgery in the lumbar and thoracic regions (2.1 and 2.2%) than it was for surgery in the cervical region (1.0%). Revision surgery and age greater than 80 years were factors contributing to a higher incidence of durotomies. The study also noted a significant association between unintended durotomy and the development of a new neurologic deficit (p < 0.001).

McMahon and colleagues reported on a series of 3000 elective spine surgeries at an academic center and noted the rate of incidental durotomies to be 3.5% in these patients. The incidence was higher (6.5%) for revision cases. Thoracolumbar cases had a higher rate (5.1%) compared to cervical cases (1.3%). When physician training was examined, residents were responsible for 49% of all durotomies. Spine fellows accounted for 26% and attending surgeons accounted for 25% of the durotomies.

An elevated incidence of durotomies has also been reported following radiation therapy to the surgical site and in patients undergoing surgery for synovial cysts, higher-grade spondylolisthesis, ossification of the longitudinal ligament (OPLL) in the cervical spine, and lumbar disc herniation through a minimally invasive tubular retractor approach.

The incidence of pseudomeningoceles is more difficult to determine because most cases are asymptomatic. Although the majority of pseudomeningoceles are found in the lumbar region, they can also occur in the thoracic and cervical spine, particularly following anterior cervical surgery for OPLL. Swanson and associates reported a 0.07% incidence of pseudomeningocele in a review of 1700 exploratory laminectomies. Schumacher and coworkers reported the incidence of pseudomeningoceles to be less than 0.1% in 3000 patients who had undergone a lumbar discectomy. Teplick and colleagues reported a 2% incidence of pseudomeningocele in a series of 400 symptomatic postlaminectomy patients examined with computed tomography (CT). None of these patients required reoperation.

The incidence of pseudomeningocele is higher in patients who have previously received radiation therapy or for patients with intradural lesions requiring an intentional durotomy. Zide and coworkers reported a higher incidence of pseudomeningocele in patients who underwent surgery for intramedullary spinal cord neoplasms following radiation therapy and in patients who had surgery for a tethered spinal cord.

Pathophysiology

A durotomy, either occult or recognized, is the initial event that leads to the development of a postoperative CSF fistula or pseudomeningocele. CSF fistulas most commonly occur in the immediate postoperative period (1 to 7 days). CSF typically passes through an incompletely healed area of the surgical wound or through a drain tract. This prevents the wound from completely healing, which in turn allows for persistence of the CSF leak and development of a defined fistulous tract.

CSF leakage through a repaired dural tear may be exacerbated by elevated CSF pressure. Transient elevation of CSF pressure can occur with the patient in an upright position or during coughing, sneezing, or straining during bowel movement. Lumbar intradural pressure is markedly elevated with an erect posture (350 to 450 mm H ₂ O), compared with supine recordings (70 to 170 mm H ₂ O). For this reason, patients at risk for CSF leakage should be kept flat in bed and treated with stool softeners in the immediate postoperative period.

Sustained elevation of CSF pressure can also contribute to the development of a CSF fistula. This is most commonly observed following repair of a myelomeningocele in patients with hydrocephalus and is typically managed with ventricular shunting to correct the abnormal CSF dynamics.

The development of a pseudomeningocele also requires an initial durotomy. If the arachnoid remains intact after the durotomy, it may herniate through the defect and subsequently form an arachnoid-lined sac filled with CSF. If the arachnoid is not intact, there is direct extravasation of CSF into the wound with eventual development of a fibrous capsule. In either case, CSF pulsations force the fluid into the muscular and superficial subcutaneous tissues ( Fig. 208-1 ). The size, shape, and location of the sac depend on the nature of the soft tissue into which the fluid is forced. In rare cases the capsule may ossify. Entrapment of nerve roots in the pseudomeningocele may actually prevent the dura from spontaneously healing ( Fig. 208-2 ).

Lumbar postmyelogram CT demonstrating a postoperative pseudomeningocele.

Intraoperative photograph during lumbar surgery demonstrating herniation of nerve rootlets (arrow) through a dural defect.

Several factors may affect the persistence or resolution of a pseudomeningocele. Teplick and colleagues suggested that if the arachnoid is intact and herniates into the wound, the communication is more likely to remain open and form a pseudomeningocele. If the arachnoid is not intact, the communication is more likely to close. Tsuji and associates suggested that the volume of the CSF leakage was more of a factor, with smaller leaks being more easily absorbed making the development of a pseudomeningocele less likely than with larger leaks. However, Bhatoe contends that a smaller durotomy leads to a higher probability of pseudomeningocele formation due to a ball valve mechanism, which permits only one-way flow of CSF. The trapped CSF then collects in the bed of the wound and an abnormal connective tissue reaction occurs, leading to poor CSF absorption.

Although the majority of durotomies heal uneventfully following primary repair, several local and systemic factors can contribute to insufficient healing with the potential development of a CSF fistula or pseudomeningocele. These factors prevent or delay healing of the dura and overlying soft tissues and include the presence of scar tissue, irradiated tissue, localized infection, or foreign body reaction. Systemic factors that impair healing include nutritional deficits, endocrine disorders (e.g., diabetes), chronic disease, and steroid administration.

Pathophysiology

A durotomy, either occult or recognized, is the initial event that leads to the development of a postoperative CSF fistula or pseudomeningocele. CSF fistulas most commonly occur in the immediate postoperative period (1 to 7 days). CSF typically passes through an incompletely healed area of the surgical wound or through a drain tract. This prevents the wound from completely healing, which in turn allows for persistence of the CSF leak and development of a defined fistulous tract.

CSF leakage through a repaired dural tear may be exacerbated by elevated CSF pressure. Transient elevation of CSF pressure can occur with the patient in an upright position or during coughing, sneezing, or straining during bowel movement. Lumbar intradural pressure is markedly elevated with an erect posture (350 to 450 mm H ₂ O), compared with supine recordings (70 to 170 mm H ₂ O). For this reason, patients at risk for CSF leakage should be kept flat in bed and treated with stool softeners in the immediate postoperative period.

Sustained elevation of CSF pressure can also contribute to the development of a CSF fistula. This is most commonly observed following repair of a myelomeningocele in patients with hydrocephalus and is typically managed with ventricular shunting to correct the abnormal CSF dynamics.

The development of a pseudomeningocele also requires an initial durotomy. If the arachnoid remains intact after the durotomy, it may herniate through the defect and subsequently form an arachnoid-lined sac filled with CSF. If the arachnoid is not intact, there is direct extravasation of CSF into the wound with eventual development of a fibrous capsule. In either case, CSF pulsations force the fluid into the muscular and superficial subcutaneous tissues ( Fig. 208-1 ). The size, shape, and location of the sac depend on the nature of the soft tissue into which the fluid is forced. In rare cases the capsule may ossify. Entrapment of nerve roots in the pseudomeningocele may actually prevent the dura from spontaneously healing ( Fig. 208-2 ).

Lumbar postmyelogram CT demonstrating a postoperative pseudomeningocele.

Intraoperative photograph during lumbar surgery demonstrating herniation of nerve rootlets (arrow) through a dural defect.

Several factors may affect the persistence or resolution of a pseudomeningocele. Teplick and colleagues suggested that if the arachnoid is intact and herniates into the wound, the communication is more likely to remain open and form a pseudomeningocele. If the arachnoid is not intact, the communication is more likely to close. Tsuji and associates suggested that the volume of the CSF leakage was more of a factor, with smaller leaks being more easily absorbed making the development of a pseudomeningocele less likely than with larger leaks. However, Bhatoe contends that a smaller durotomy leads to a higher probability of pseudomeningocele formation due to a ball valve mechanism, which permits only one-way flow of CSF. The trapped CSF then collects in the bed of the wound and an abnormal connective tissue reaction occurs, leading to poor CSF absorption.

Although the majority of durotomies heal uneventfully following primary repair, several local and systemic factors can contribute to insufficient healing with the potential development of a CSF fistula or pseudomeningocele. These factors prevent or delay healing of the dura and overlying soft tissues and include the presence of scar tissue, irradiated tissue, localized infection, or foreign body reaction. Systemic factors that impair healing include nutritional deficits, endocrine disorders (e.g., diabetes), chronic disease, and steroid administration.

Clinical Features

CSF fistulas and pseudomeningoceles may present with a variety of signs and symptoms. The diagnosis of a cutaneous CSF fistula is most often established by inspection of the patient’s wound. A clear, watery discharge that produces a clear halo surrounding a central pink stain on an absorbent surface is assumed to be CSF, particularly if the leakage is augmented by upright posture or a Valsalva maneuver or is associated with postural headaches. When headaches occur, they are typically more severe with an erect posture and are relieved in a recumbent position. Headaches are secondary to the reduction of the CSF volume when the CSF loss through the fistula exceeds its production. The lowered intracranial pressure induces traction on pain-sensitive structures, such as meninges and blood vessels. In the recumbent position, traction is reduced and the pain is relieved. Fever or evidence of meningismus may suggest the possibility of bacterial meningitis and may be the presenting clinical picture in patients with an unrecognized CSF fistula.

Pseudomeningoceles may be more difficult to identify because most remain asymptomatic. The time interval between surgery and the onset of symptoms may range from months to years. Initial signs and symptoms in the lumbar region include localized back pain and postural headaches. Localized nerve root entrapment or adhesions of roots to the dural edges of the pseudomeningocele can produce radicular symptoms. With gradual enlargement, the pseudomeningocele may present as a fluctuant mass at the surgical site. The mass may enlarge with coughing or sneezing and may be tender to palpation. In the cervical region, patients with pseudomeningoceles may present with progressive or delayed myelopathy.