Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature.

Otologic Causes Of Meningitis
Carrie Roller, M.D.
February 10, 2000

This morning I will begin with some of the basics of epidemiology and clinical course of meningitis. Next I will focus on otolaryngologic causes of meningitis. By far the most frequent causes are congenital deformities, trauma, and infection. Finally, as hearing loss is the most frequent sequela in survivors of meningitis, I will discuss post meningitic hearing loss including possible etiologies and suggested follow up.

Meningitis is defined as inflammation of the meninges. Causative pathogens may be bacterial, viral, or fungal. However, we are primarily concerned with bacterial meningitis. There are 25,000 cases of bacterial meningitis reported every year in the United States. Somewhere between 7 and 10% of these cases die of their disease. There has been a significant improvement however, over the pre-antibiotic era, when mortality was reported at up to 90%. Meningitic inflammation is due to the presence of infection within the subarachnoid space. The subarachnoid space contains the cerebral spinal fluid and this space extends throughout the cerebral axis. Infection and inflammation of the CSF and subarachnoid space does extend through the brain including the ventricles, the spinal cord, and the optic nerves. The anatomy and the extent of the subarachnoid space explain the cardinal symptoms of bacterial meningitis, which are headache, fever, neck stiffness (or nuchal rigidity), photophobia and mental status changes. Meningo coccemia, which is infection with streptococcus meninginitis, may be accompanied by rash, seizures, and cranial nerve palsies are associated with increased intercranial pressure.

After initial stabilization of the patient suspected of having meningitis, imaging of the brain consisting of contrast enhanced CT or MRI is performed in order to rule a mass lesion, which could cause herniation from a lumbar puncture. An MRI is preferred to evaluate for subdural empyema, epidural abscess, brain abscess or lateral sinus thrombosis. Once an intercranial mass has been ruled out, the lumbar puncture is performed to obtain cerebrospinal fluid for diagnostic purposes. Broad-spectrum antibiotics are ideally initiated after the lumbar puncture for diagnostic reasons, however if any delay occurs in the work up antibiotic administration takes precedence.

Different types of meningitis may often be differentiated based on laboratory CSF findings. Bacterial meningitis tends to have the most striking leucocytosis with a predominance of polymorphoneuclocytes, protein tends to be elevated and glucose is low in patients with bacterial meningitis.

Bacteria responsible for meningitis vary with patient age. However 3 primary bugs are responsible for 75-85% of all cases of bacterial meningitis worldwide. These 3 are streptococcus pneumonia, neisseria meningitidis, and haemophilus influenzae. The incidence of haemophilus influenzae meningitis has decreased over 90% since the introduction of the haemophilus influenzae type B or HIB vaccine introduced in 1990.

In a review of 79 patients with otologic sources of meningitis Very et al found that the vast majority rose from otitis media either acute or chronic. Acute otitis media was the source in 40% of patients, chronic otitis without cholesteatoma was found in 15%, chronic otitis with cholesteatoma is found in 21% and traumatic temporal bone fracture in 17%. The remaining 5% was spilt evenly between surgical and congenital etiologies.

There are several potential mechanisms for the spread of bacteria from the middle ear space and the mastoid into the subarachnoid space and cerebral spinal fluid. The most common is hematogenous. Bacteria from the middle ear space enter the blood stream and gain entry to the CSF to through the choroid plexus. Labyrinthitis may contaminate CSF by way of the lamina cribrosa of the internal auditory canal. The middle ear or mastoid infection may enter CSF by a direct extension through thrombophlebitis of the mastoid emissary vein or through preformed congenital or traumatic pathways.

As I mentioned earlier in as much as 40% of cases of meningitis of otolaryngologic etiology an acute otitis media is present. However, of almost 4,000 cases of acute otitis media studied prospectively in Thailand less than .02% developed meningitis. In otitis media complicated by meningitis a myringotomy should be performed if fusible and the incision should be wide to allow for continued drainage. Middle ear culturing actually have very low correlation with CSF findings. A low 17% correlation between pathogens identified in the middle ear and pathogens identified in the CSF has been reported. Pneumococcus is the pathogen most frequently isolated from the CSF in patients with acute otitis media.

Mastoiditis may complicate acute otitis media or chronic otitis media. Coalescent mastoiditis with intracranial complications such meningitis requires drainage through both wide myringotomy and mastoidectomy. Chronic otitis media is of course associated with significantly more pathology than acute otitis media. Large studies with patients of chronic otitis media followed long term have showed that as many of 1 in 200 people with chronic otitis media will develop intracranial complications, meningitis in half of those. 26% of people with one intracranial complication will have multiple complications at the same time. Mortality has also been to be higher in meningitis associated with chronic otitis media than with acute otitis. Infections are often polymicrobial with proteus, pseudomonas and anaerobes frequently isolated. CSF cultures however generally bear little resemblance to those of the ear.

The presence of cholesteatoma in chronic otitis media significantly increases the likelihood of intracranial complications. In the pre-antibiotic era, chronic otitis media with cholesteatoma had a rate of intracranial complication of 1 in 20 with a mortality rate of 82%. As many as 7.5% of patients with untreated cholesteatoma may develop an intracranial complication. The mean interval between the development of disease and complication is 11.9 years. Meningitis is the most common intracranial complication of cholesteatoma. Cholesteatoma can cause intracranial infection hematogenously or via direct erosion through the cranium. Treatment is mastoidectomy, which is ideally performed when the patient is medically stable. Extent of mastoidectomy is determined by the extent of the disease.

The vast majority of cases of meningitis derive from hematogenous spread of bacteria whether from the middle ear, the nasopharynx or other anatomic source. The etiology may not always be clear. However, if meningitis is recurrent it becomes much more likely there is an underlying disease process or an occult anatomic abnormality, which is acting as a portal of entry for bacteria into the subarachnoid space. Recurrent meningitis is rare entity but it a high association with otolaryngologic disease.

A study published in 1978 revealed that 9 of 290 cases of meningitis were recurrent, but of those 90% had underlying ear and sinus pathology. Streptococcus pneumonia is again the most common pathogen associated with recurrent meningitis. Any case of recurrent meningitis should prompt a search for underlying anatomic abnormality.

Drummond at all estimate that up to 1/3 of children with recurrent meningitis have an underlying immune deficiency such as congenital asplenia. They also estimate that 1/3 of these children will have an underlying otolaryngologic disorder such as a CSF leak. A larger study, in 1956 found a 52% of otolaryngologic etiologies from recurrent meningitis. These numbers serve to emphasize the need for a thorough evaluation of individuals with recurrent meningitis.

Drummond at all therefore recommend the following evaluation to screen for likely etiologies in children. The first step is a basic hearing evaluation. This step is recommended in all cases of meningitis due to the high rate of deafness as a sequela of meningitis. In this case it also screens for hearing loss that may be associated with congenital inner ear malformations. The next step is to obtain a high resolution CT of the head including coronal images of the sinuses and fine cuts through the temporal bones. This is to evaluate for defects of the skull base and for inner ear malformations that may be predisposed to CSF leak. Finally, immunologic workup including a complete blood count, immunoglobulin levels and subclasses and compliment levels is recommended. Recommendations regarding the work up are similar for adults as for children however more emphasis is placed on the discovery of the anatomic problems.

In cases of recurrent meningitis suspicion should be high for anatomic abnormality which allows bacterial pathogens a pathway into the CSF. Dehiscence in the temporal bone may or may not be accompanied by CSF leakage. Clear otorrhea that is positive on a dextrose stick is highly suspicious and the presence of Beta 2 transferrin is specific and sensitive. Occasionally, CSF will accumulate in the middle ear and drain through the eustachian tube in which case CSF otorrhea may occur. Potential etiologies of dehiscece in the temporal bone in the temporal bone are primarily traumatic, surgical and congenital.

Traumatic temporal bone fractures may lead to cerebral spinal fluid leaks. Patients with CSF fistula have reported 25% risk of developing meningitis. The most common organism isolated in this group is strep pneumonia. 50% of posttraumatic bacterial meningitis occurs within 2 weeks of injury, however the onset of meningitis may also occur as soon as 1-2 days after the initial injury or it may be delayed for decades.

Surgery may be a cause of meningitis by the acute introduction of organisms through the surgical wound or by the creation of defects in the skull base which allow regressive cerebral spinal fluid and ingressive bacteria. CSF rhinorrhea from cribriform plate injury is a well-known potential sequela of sinus surgery, and CSF otorrhea may occur as sequela of otologic surgery.

Welling et al report a 7.5% rate of CSF leak and a 3.8% rate of meningitis after vestibular schwannoma surgery. Mastoid surgery in general can result in CSF leakage or encephalocele. Congenital malformations of the temporal bone can lead to CSF fistula in recurrent meningitis. Congenital encephaloceles in inner ear malformations comprise the largest two groups in this category. The Mondini malformation is the congenital ear deformity most commonly associated with meningitis in the literature. The Michel malformation is a less common and more severe deformity along the same developmental lines as the Mondini. In cases of both encephalocele and congenital ear malformations, strep pneumonia is again the most common pathogen in meningitis.

Tegmen defects are found in up to 20% of random autopsy specimens. The etiology of these is unclear. It is possible that many of these are acquired, however it appears that there is a very high incidence of congenital bony dehiscents from failure of fusion of the bony plate. Encephalocele which presents with a visible abnormality are found in up to 1in 1000 children and non-visible encephalocele generally is discovered when it becomes symptomatic through a complication such as meningitis. And otherwise occult encephalocele becomes symptomatic present in only in 10, 000 individuals in the general population.

Treatment of an encephalocele is surgical. Non-functional brain tissue is removed and repair of the dural defect is done. After extradural repair is recommended to offer direct access for both resection of herniated brain tissue and repair of the dura.

Congenital malformations of the inner ear may frequently allow the passage of bacteria into the subarachnoid space, thus causing recurrent meningitis. As many as 20% of children with congenital sensorineural hearing loss will have CT evidence of subtle to severe abnormalities of the inner ear. About 65% of these will have bilateral abnormalities and the other 35% unilateral. A range of abnormalities exists, the severity of which primarily depends on the stage at which the development of the inner from the otocapsule is arrested or impaired. Certain types of malformations show a tendency to develop recurrent meningitis, the pathogenesis of, which is best understood from an anatomic and embryologic view point.

Congenital inner ear malformations may be understood best with reference to embryology. The otic capsule develops at 4 weeks gestation and begins differentiation into the cochlear and vestibular structures. Differentiation is complete at around 8 weeks. Interruption of this process at certain points leads to characteristic inner ear malformations. For example interruption of the development before 4 weeks leads to complete agenesis of the labyrinth, known as the Michele abnormality. A common cavity forms shortly after that and development is interrupted at 7 weeks causing the classic Mondini malformation.

In 1863, Michele described a case of complete labyrinthine aplasia, this is a very rare anomaly which results from arrest in the development of the otic capsule for the otocyst at 4 weeks gestation.

There is complete absence of the cochlea and the vestibule. The internal auditory canal is hypoplastic and the middle ear cavity is expanded due to the absence of the cochlea. The concavity of the medial wall of the middle ear space is useful in distinguishing this abnormality from labyrinthitis ossificans.

Mondini malformations are a commonly reported type of inner ear malformation. It may be unilateral, it may be bilateral or accompanied by a different malformation on the other side. Genetically both dominant recessive forms and sporadic forms have been described. There is association with a number of syndromes. Variably some hearing may be present in an effected ear and the presence of some neuro sensory function allows for the use of conventional amplification and in some cases cochlear implants. Many morphologies of inner ear malformations have been labeled as Mondini malformations however the malformation described by Mondini in 1791 is a very distinct entity. The classic Mondini malformation is due to arrested development of the labyrinthian structures at 7 weeks when the formation of the inter scaler septum is incomplete. The normal cochlea has 2 -½ to 2 -¾ turns. But the Mondini cochlea has a dilated basil turn with a common apical cavity instead of the normal upper turns for a total of 1-½ turns. Cochlear Mondini malformations may be accompanied by variable degrees of vestibular deformity. Dilation of the vestibule and defects of the stapes footplate are frequently seen with the cochlear malformation of Mondini and these are likely responsible for the recurrent meningitis reported in many patients with Mondini malformations.

Patients with congenital labyrinthian anomalies who show a propensity for CSF leak or recurrent meningitis should undergo a procedure to create a safe ear. Obliteration of the labyrinthian cavity may be performed.

Hearing loss is the most common sequela effecting meningitis survivors. Reports of the rate of hearing loss after meningitis vary from 5-35% in the literature. A recent study from The University of Alabama reveal that 13.7% of 432 children with meningitis developed hearing loss. In 75% of cases hearing loss was bilateral, and in 22% the hearing loss fluctuated for up to a year before stabilizing. Patients who do not have measurable hearing loss at the time of discharge from the hospital are actually unlikely to later develop hearing loss as a late sequela.

There are several mechanisms proposed for hearing loss secondary to meningitis. The basic process is that inflammation hypoxia and increased intracranial pressure can damage many structures including the central auditory pathoid structures, the 8 th cranial nerve. The vascular compromise to the inner ear can be damaging to fragile sensory organs. And finally, labyrinthitis can lead to cochlear ossification. Labyrinthitis ossificans is ossification within the bony membranous labyrinths. This process appears to be the result of labyrinthitis a source of which may be from the blood stream, the middle ear or from the meninges. Other proposed mechanism includes endotoxin mediated inflammatory response. The ossification process begins to appear within 3 months of the onset of meningitis and may be complete by 1 year. This process is often bilateral and causes severe sensory neural hearing loss. The presence of bone within the cochlea can create problems with the placement of electrodes during cochlear implantation.

Factors that have been implicated as high risk for post meningitic hearing loss have been described by a number of authors. A retrospective study of 432 children with meningitis found that a statistically significant increase in hearing loss in association with increased intracranial pressure, male sex, decreased levels of glucose in the CSF, and infection with streptococcus pneumonia. It did not find any protective effect from the administration of steroids.

Any episode of meningitis warrants an audiogram prior to the patient’s discharge from the hospital. It is recommended that any finding of hearing loss be followed with monthly reevaluation until the hearing loss stabilizes. After that audiologic reevaluation should be continued on a less frequent basis down to one year in most patients. If meningitis is recurrent, further workup is warranted. The high incidence of otologic and rhinologic abnormalities in individuals with recurrent meningitis warrants a CT of the temporal bones, skull base and paranasal sinuses. Drummond also recommended a medilogic investigation, as 21% of patients with recurrent meningitis have been to find immune deficiencies.

Case Presentation:

JC is a 75-year-old woman who arrived at the Ben Taub Emergency Room with fever and mental status changes. The family were available only to give this history to the triage desk, and then departed, not to return for many days. The history of this patient was therefore unknown.

Physical examination revealed a well-nourished, Spanish-speaking woman who was lethargic and speaking incoherently at times. Her temperature was 102 orally. She was tachycardic to106 bpm, and she became agitated when attempts were made to move her head or her extremities. Physical examination was otherwise unremarkable.

Laboratories revealed a white blood cell count of 18,900 with predominantly polymorphonucleocytes. Her complete blood count and chemistries were essentially unremarkable otherwise.

A presumptive diagnosis of meningitis was made. A CT of the head was ordered to evaluate for mass lesions such as an abscess which might create a risk of herniation with lumbar puncture. No mass lesions were found, however there was pneumocephalus present at the border of the left temporal bone. Neurosurgery and Otolaryngology consults were immediately called, and a lumbar puncture was performed. After specimens were obtained, the patient was given empiric, broad-spectrum antibiotics.

Otolaryngologic exam revealed intact tympanic membranes with no definite middle ear fluid. There was a small amount of whitish exudate in the right external auditory canal. Particular care was needed in positioning the head due to the patient’s obvious discomfort with movement. Myringotomy was performed, with no return of fluid. The nasal mucosa was somewhat inflamed, but there was no purulence. Head and neck examination was otherwise unremarkable.

Laboratory studies of the cerebrospinal fluid revealed 2,975 white blood cells, 93% of which were neutrophils. Total protein was 540 mg/dL (high) and glucose was 40 (low). Gram’s stain revealed multiple white blood cells, but no organisms.

CSF cultures were negative, but blood cultures taken on admission grew Streptococcus pneumoniae.

The patient’s physical condition began to improve after 24 hours of IV antibiotics.

She next underwent CT of the temporal bones. This revealed a defect in the posterior aspect of the left temporal bone with soft tissue vs fluid in the adjacent mastoid air cells.

The patient was unable to participate fully enough to obtain an adequate audiogram. ABER revealed a moderate left-sided sensorineural hearing loss.

The family ultimately returned and were questioned regarding the patient’s medical history. She had no known history of otologic disease or head trauma, and her hearing had been noticeably impaired for an indeterminate amount of time.

Once the patient’s medical condition was clearly stabilized, she was taken to surgery to explore the left temporal bone. A mastoidectomy was performed, and a cerebellar encephalocele was found in the area of the sinodural angle. The encephalocele was removed and the dural defect was repaired with a fascia graft, followed by mastoid obliteration with abdominal fat. She did well and was discharged from the hospital after administration of IV antibiotics for a total of three weeks from the onset of her meningitis.

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