Key Words: Otitis, Malignant, Osteomyelitis, skullbase.
Skull base Osteomyelitis (SBO) is one of the devastating infection with potential morbidity which warrants a high degree of suspicion when formulating a differential diagnosis for Otological skull base lesions. Malignant external Otitis (MEO) is a more localised form of SBO which usually spreads to the preauricular Soft tissues, cartilage and bone with cranial neuropathy. If untreated it may extend throughout the skull base, infra-temporal fossa, parapharyngeal space, nasopharynx along with intracranial extension. The most typical patient being an elderly, uncontrolled diabetic with pseudomonal infection and facial palsy.
Skull Base Osteomyelitis is one of the devastating infection with potential morbidity and mortality which warrants a high degree of suspicion when formulating a differential diagnosis for otologic and skull base lessions. Malignant External Otitis is a more localised form of skull base Osteomyelitis which usually spreads to peri-auricular soft tissue, cartilage and bone. If untreated it may extend throughout the skull base, infratemporal fossa, parapharyngeal space, nasopharynx and finally spreads intracranially. Other Pathologies in this area with similar symptoms and signs are wegener`s granulomatosis, Carcinoma of temporal bone, carcinoma naropharynx, metastatic lesion to clivus, pagets disease, fibrous dysplasia and basilar skull fracture. Osseous skull base is made up of tympanic ring, mastoid, petrous, maxillary, ethmoid, sphenoid, and occipital bones. Osteomyelitis of the skull base involves an infection in the diploic cancellous bone of the outer and/or inner cortical and periosteum, the dura, surrounding soft tissue, major Vessels and cranial nerves of skull base.
The original report was by Melzter and Kelemen 21 in 1959, described as a case of Pyocyaneus. Chandler 4 in 1968 was credited with coining the term malignant otitis externa. The term malignant is used to emphasize the serious nature of this infection, as in the original historical report 7 of the 13 patients died. Various alternative terms used are (synonyms) – Progressive, Fulmilnant, invasive and necrotising external Otitis.
Lucent etal 17 described the term MEO as a dangerous misnoner. But despite these misgivings the term MEO is widely used in the literature. NEO has been offered as an alternative term of MEO which is a more limited form of infection, isolated to the skin and cartilage of the EAC which may not always be associated with pseudomonas infection, but may be with others like staphylococcus.
In a comprehensive review of literature on Osteomyelitis, Waldrogel etal 31 noted three fundamentalfactors for the pathogenesis – a contageous focus of infection, haematogenous seeding and microvascular diseases. Known microangiopathy of elderly diabetic with poor glucose control compromises blood supply to the affected area which limits effective immunologic response and host resistances. The most common factor identified in the majority of the cases with MEO is the existence of elderly diabetes mellitus (90%) and majority are aged 60 years or older. Other predisposing factors are use of hearing aid, CSOM, leukemia, alcoholism, kernicterms, tuberculosis, swimmers etc., Rubin etal 25 in a retospective study found that 61.5% of patients with MEO had unsterile tap water irrigation of their ear within two weeks of onset of symptoms which is iatrogenic by physicians. Some of the other organisms have been identified with MEO and SBO in both adult and children are salmonella 28 Mycobacterium tuberculosis 14, Actionomyces 30, Aspergellous flavus 22, Aspergillons fumigatus 5. But pseudomonas is found in 99.2% of cases of MEO 15. Other organisms involved are staphylococous aureus 15 and epidermidis 2. The pathogenesis of SBO as outlined by Nado etal 24 begins in the epithelium of the EAC and extends into the retromandibular fossa through the fissure of Santorini into the parotid space or through the tympanomastoid suture. Facial palsy is typically due to soft tissue infection around the Stylomastoid foramen.
Infection spreads to mastoid tip and Jugular foramen with potentialthrombosis of the sigmoid sinus and lower cranial nerve paresis. Transvenous thrombosis and sepsis may affect lateral sinus, superior and inferior petrosal sinues with progressive osteomyelitis advancing into the petrous apex, middlefossa, base of sphenoid and clivus of the posterior fossa, contralateral temporal bone and skullbase. Posterior spread into the occipital bone elicits neural pain and potential compromise of the contents in the posterior cranial fossa. It may also spread anteriorly into the temporal fossa and facial bone.