Cerebrospinal Fluid, Otorrhea and Encephalocele

Introduction

Cerebrospinal fluid (CSF) leak of the temporal bone results from having a connection between the air-containing spaces of the temporal bone and the intracranial subarachnoid space. The connection is by way of defect(s) in the tegmen mastoideum or tegmen tympani with or without the presence of a concurrent encephalocele ( Fig. 144.1 ) or meningoencephalocele. CSF collects in the middle ear and mastoid, and the egress of fluid is by way of a defect in the tympanic membrane or bony ear canal resulting in CSF otorrhea. With an intact tympanic membrane, fluid can drain down the Eustachian tube causing CSF rhinorrhea. The most common etiology of CSF otorrhea is a head injury with a fracture of the temporal bone, followed by iatrogenic injury or erosive changes from chronic otomastoiditis. Spontaneous or idiopathic CSF otorrhea is rare. In the pediatric population, CSF leaks are commonly associated with congenital malformations of the temporal bone. Congenital temporal bone CSF fistulas are rare and categorized as perilabyrinthine or translabyrinthine depending on the route of CSF transmission. These patients are more likely to present with meningitis or sensorineural hearing loss. Adults with spontaneous CSF otorrhea typically present with common otologic complaints of unilateral aural fullness or hearing loss, and typically have normal inner ear anatomy. As a result, the diagnosis can be elusive. A common initial diagnosis is chronic serous otitis media (CSOM). In this situation, a CSF leak becomes highly suspicious following myringotomy or placement of a tympanostomy tube. This often results in clear, watery otorrhea that is persistent and frequently pulsatile. Confirmation of the fluid as CSF can be achieved by obtaining an assay for beta-2 transferrin, which is highly sensitive and specific for detection of CSF, though vitreous and perilymph also contain the protein. Meningitis with concurrent middle ear effusion is a rare and more serious presentation. Chronic intracranial hypertension, such as that seen with benign or idiopathic intracranial hypertension (IIH), is known to predispose to CSF leaks, including CSF otorrhea. This syndrome is particularly prominent in obese, middle-aged women, and may be associated with headache, pulsatile tinnitus, and visual changes. There has been much investigation in trying to understand the mechanism for elevated ICP, and linking this process to the underlying pathophysiology seen in patients with IIH. Numerous reports have established an association between elevated intracranial pressure (ICP) and spontaneous CSF otorrhea. Aberrant arachnoid granulations overlying the posterior fossa plate and the floor of the middle fossa potentially leading to bony erosion and CSF leak have also been reported in the literature. Unfortunately, due to the rare incidence of this disease, an established pathophysiology for spontaneous or idiopathic CSF leak is lacking. Patients with a history of chronic otitis can develop cholesteatoma that may erode into the otic capsule as well as through the middle or posterior fossa plates. Primary or metastatic malignant tumors to the temporal bone may also lead to bone erosion and CSF leak. In adults, the most common tumors are epithelial tumors and paragangliomas. In children, it is rhabdomyosarcoma.

Once the diagnosis is made, surgical repair is warranted because of the increased risk for developing central nervous system complications and infections, such as meningitis. An exception is CSF leak secondary to fractures of the temporal bone. Bed rest and elevation of the head results in spontaneous resolution in up to 90% of these patients; however, a lumbar drain (LD) may also be required with recalcitrant high volume leaks. Iatrogenic injury during mastoid or middle fossa surgery is typically recognized at the time, and immediate repair obviates subsequent management. The options for surgical repair vary according to the size and site(s) of the leak.

Key Operative Learning Points

• 1.

  CSF otorrhea may be acquired or spontaneous.

• 2.

  Imaging is essential in determining the size and location of a defect(s).

• 3.

  Regardless of the etiology, surgical repair is recommended, and the surgical technique is dictated by the site of the leak. An exception is CSF leak secondary to trauma, which typically resolves spontaneously.

• 4.

  All surgical repairs should employ a multilayer reconstructive technique, preferably with autologous tissue to minimize the chances of postoperative infection and foreign body reactions. The sources of anatomic materials include bone, free tissue grafts, or vascularized flaps

• 5.

  Surgical repair can be performed via transmastoid or middle fossa approaches or a combination of these. Obliteration of the middle ear may be required in particular circumstances.

• 6.

  Synthetic materials, such as bone cement substitutes also may be used in conjunction with autologous material.

• 7.

  CSF diversion via LD is often employed in the immediate postoperative period, especially in the repair of spontaneous middle fossa defects.

• 8.

  Intraoperative measurement of intracranial pressures may reveal elevated ICP in patients with spontaneous leaks, particularly in middle-aged obese women. However, pressures may be deceivingly normal as the result of active CSF egress through the defect.

Preoperative Period