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Idiopathic osteomyelitis at the base of the skull.

Abstract: Osteomyelitis of the skull base is a rare disorder, and even more so when the etiology is noninfectious. Symptoms are noisome and include headache and cranial nerve deficits. Because of the possibility of neoplasia, thorough evaluation, accurate diagnosis, and effective treatment are mandatory. In the case reported herein, a 58-year-old man with a 3-month history of symptoms is presented. Physical examination disclosed cranial nerve involvement. Nasopharyngeal biopsy and culture in combination with MRI and a gallium bone scan established the diagnosis of osteomyelitis at the base of the skull. The patient was effectively treated with antibiotics and had a complete recovery.

Key Words: osteomyelitis, skull, idiopathic

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Most cases of osteomyelitis at the base of the skull result from the inadequate treatment of localized, chronic otitis externa. (1-3) Osteomyelitis of the skull base has also been described as arising from infection of the paranasal sinuses and the mandible or maxilla due to odontic caries. (3) Osteomyelitis in the cervical spine may arise following radiotherapy to the head and neck (4,5) with Pseudomonas aeruginosa as the most common organism recovered. (1-3) In contrast, idiopathic osteomyelitis at the base of the skull is quite rare.

The most frequent symptom occurring in such patients is headache; concomitant pain and cranial nerve involvement without an obvious source of infection make the clinical presentation more confusing and lead to a delay in diagnosis and treatment. We report a case of osteomyelitis at the base of the skull, which had no obvious contiguous infection or other predisposing factors. The diagnosis, management, and therapeutic options are discussed.

Case Report

A 58-year-old nondiabetic male had a 3-month history of headache, diplopia, hoarseness, choking, and hearing impairment without sinusitis or otologic infection. One month before our evaluation, a CT was performed at another hospital and showed an osteolytic lesion with infiltrative margins and heterogeneous contrast enhancement, primarily involving the central base of the skull and covering both the basisphenoid and basiocciput. Multiple endonasal, telescope-guided nasopharyngeal biopsies were obtained of the mucosal neogrowth, yet the pathologic diagnosis was inconclusive, indicating an inflammatory process. Because of the persistence and worsening of symptoms, the patient was admitted to our hospital for further assessment. With a similar initial clinical impression, biopsies were repeated by obtaining tissue from the nasopharyngeal mucosa and central skull base using an endoscope and CT-guided methods. As before, the results were nonspecific.

A more comprehensive physical examination revealed extensive lower cranial nerve palsies, involving cranial nerves VI, VIII, IX, and X, as evidenced by the collective manifestations of hearing impairment, hoarseness, and dysphagia. Right-sided involvement of the central skull base and adjacent structures was verified by the presence of geographic enhancement as demonstrated by MRI (Figs. 1 and 2). In addition, a gallium bone scan showed increased uptake in the base of the skull. These findings, taken together, suggested an inflammatory etiology rather than a neogrowth. Therefore, an intentional, deep-bite nasopharyngeal culture was obtained, yielding the presence of Pseudomonas aeruginosa. Accordingly, the diagnosis of osteomyelitis was made, involving the skull base, associated neuroforamina, and the transmitted cranial nerves. Along with a type I thyroplasty for right-sided vocal palsy, and a myringotomy with ventilation tube insertion for middle ear effusion, the patient was administered oral ciproxin. Three months later, a repeat gallium bone scan showed reduced, but persistent uptake, consistent with healing and resolution of the osteomyelitis, even though the patient's hearing had not been restored. Shortly thereafter, however, the patient's symptoms abated entirely and after a 6-month period, a repeat MRI revealed a dramatic disappearance of the skull base lesion (Fig. 3).

Discussion

Osteomyelitis at the base of the skull is a relatively uncommon medical condition. The most commonly encountered clinical scenario is a diabetic patient with an inadequately treated chronic external otitis who presents with temporo-occipital pain. Alternatively, a sinus infection leads to the development of osteomyelitis in the frontal bone with extension to the maxilla. (1-3) Persistent headache is the cardinal symptom with hoarseness and aspiration secondary to vocal cord palsy, an accompaniment of a severe inflammatory process in the jugular foramen. In these cases, on initial presentation, the patient is usually more alert to the acute illness, and the diagnosis is less confusing.

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Atypical (idiopathic) osteomyelitis of the skull base, however, occurs much less frequently and is not associated with otitis externa or sinusitis. Furthermore, it involves the sphenoid and occipital bones rather than the temporal bone. (6) Initially, patients have headaches as their only symptoms, with subsequent cranial neuropathies. As is often the case, and occurred in the case presented herein, there were no obvious infectious sources, predisposing factors of diabetes, immunodeficiency, or microvascular disease.

Maintaining a high index of suspicion is of the utmost importance in making a timely diagnosis of osteomyelitis of the skull base. Unexplained headaches associated with neurologic deficits should alert the physician to the possible presence of osteomyelitis. Other causes, such as nasopharyngeal malignancy, metastatic lesions, or chronic granulomatous disorder must be excluded. (7)

MRI and gallium bone scans are the standard tools used to assess the severity and extent of osteomyelitis. Imaging of the skull base in the setting of cranial neuropathy and probable infection is best achieved with MRI, which has the advantage of superior soft tissue discrimination around the skull base as compared with CT. For follow-up purposes, the gallium bone scan is best used to delineate the transition from active to inactive osteomyelitis in the skull base.

Diagnosis is confirmed after the skull base biopsy and gallium bone scans are complete. Appropriate antibiotic therapy should be used against the pathogenic organism identified by culture after the diagnosis is established. In our case, Pseudomonas aeruginosa, the most common pathogen in osteomyelitis, was isolated. Gram negative osteomyelitis of the skull base is difficult to treat because high levels of antibiotics are necessary to achieve minimal inhibitory concentrations. (2) The tissue uptake of antibiotics in bone is a function of vascularity and indicates the presence of concomitant disease. Small vessel disease, especially in diabetics, further compromises antibiotic uptake and tissue distribution. (1,3) Selection of an oral antibiotic with excellent activity is particularly important in cases requiring chronic antipseudomonal therapy. (10) Osteomyelitis of the skull base should be treated with antibiotics for at least 6 weeks. Hyperbaric oxygen therapy may play a role in the management of chronic, refractory osteomyelitis of the skull base. (7,8) The role of surgery is confined to biopsy and possible drainage when an associated abscess is present. (9)

In conclusion, osteomyelitis of the skull base should be considered in patients with unexplained headaches and neurologic deficits, which may mimic nasopharyngeal neoplasm and is recalcitrant to conventional medical treatment. It can occur in the absence of an obvious source of infection and predisposing factors such as diabetes mellitus, systemic immunocompromise, or microvascular disease. Progressive neurologic sequelae and a mortality rate in excess of 50% (3) are the consequences of delayed diagnosis and treatment. With early intervention, cranial neuropathies resolve slowly after effective antibiotic therapy. MRI is a useful and reliable tool for monitoring the response to treatment and evaluating recurrence. Although it is not a surgical disease, osteomyelitis at the base of the skull has a much better prognosis when diagnosed and treated properly.

References

1. Grobman LR, Ganz W, Casiano R, et al. Atypical osteomyelitis of the skull base. Laryngoscope 1989;99:671-676.

2. Magliulo G, Varacalli S, Ciofalo A. Osteomyelitis of the skull base with atypical onset and evolution. Ann Otol Rhinol Laryngol 2000;109:326-330.

3. Chandler JR, Grobman L, Quencer R, et al. Osteomyelitis of the base of the skull. Laryngoscope 1986;96:245-251.

4. Balm AJ, Tiwari RM, de Rijcke TB. Osteomyelitis in the head and neck. J Laryngol Otol 1985;99:1059-1065.

5. Strauss M, Kaufman RA, Baum S. Osteomyelitis of the head and neck: sequential radionuclide scanning in diagnosis and therapy. Laryngoscope 1985;95:81-84.

6. Chang PC, Fischbein NJ, Holliday RA. Central skull base osteomyelitis in patients without otitis externa: imaging findings. AJNR Am J Neuroradiol 2003;24:1310-1316.

7. Sie KC, Glenn MG, Hillel LH. Osteomyelitis of the skull base, etiology unknown. Otolaryngol Head Neck Surg 1991;104:252-256.

8. Amedee RG, Mann WJ. Osteomyelitis of the skull base-an unusual manifestation. Am J Otology 1989;10:402-404.

9. Ducic Y. Management of osteomyelitis of the anterior skull base and craniovertebral junction. Otolaryngol Head Neck Surg 2003;128:39-42.

10. Castro C, Sanchez E, Delgado A, et al. Ciprofloxacin implants for bone infection. In vitro-in vivo characterization. J Control Release 2003;93:341-354.

Yu-Che Hsiao, MD, Jin-Chin Lee, MD, Bor-Hwang Kang, MD, and Yaoh-Shiang Lin, MD

The Department of Otolaryngology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China.

Reprint requests to Yaoh-Shiang Lin, MD, Department of Otolaryngology-Head and Neck Surgery Tri-Service General Hospital, National Defense Medical Center No. 325, Sec. 2, Cheng-Kung Road, Neihu District, Taipei, Taiwan 114, R.O.C. Email: yskuolin@ndmctsgh.edu.tw

Accepted March 24, 2006.

RELATED ARTICLE: Key Points

* Osteomyelitis at the base of the skull is most often secondary to an infectious process.

* A noninfectious etiology for osteomyelitis at the base of the skull is rare.

* Headache, with cranial nerve deficits, should raise the suspicion of osteomyelitis at the base of the skull.

* A thorough history and physical examination, nasopharyngeal biopsy with culture, MRI, and a gallium bone scan can secure the proper diagnosis.

* Oral antibiotics are effective in resolving osteomyelitis and serve as the mainstay of treatment.
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Author:Lin, Yaoh-Shiang
Publication:Southern Medical Journal
Article Type:Disease/Disorder overview
Geographic Code:1USA
Date:Oct 1, 2006
Words:1582
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