Discussion
Various etiologies are described in the literature as primum movens of subdural empyema including paranasal sinusitis (Table 1).
For the first time, we present an unusual case described in literature of a parietal subdural empyema secondary to acute odontogenic sinusitis, resulting from a tooth extraction (Table 2). According to Clayman et al., odontogenic sinusitis accounts for approximately 10% of cases of all maxillary sinusitis. The microbiology of rhinosinusitis and odontogenic maxillary sinusitis are thought to be different; in fact it is universally accepted that Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are commonly associated to upper respiratory tract sinusitis, whereas the typical odontogenic infection is a mixed aerobic/anaerobic infection, with a prevalence of anaerobic species (Streptococci, Bacteroides, Proteus, and coliform bacilli). Literature data confirm that more than 70% of rhinosinusitis intracranial complications are caused by Streptococci species, 15 to 20% by Staphylococcus aureus and 7% by Haemophilus species.
As our cultural examination revealed, the presence of Bacteroides in the subdural empyema was indicative of a relationship between such complication and the recent tooth extraction.
The roots of the maxillary premolar and molar teeth are situated below the sinus floor; in particular the second molars roots are the closest to the floor (mean distance of 1.97mm). These short distances explain how oroantral fistula may be responsible for the development of maxillary sinusitis that is generally characterized by a chronic course.
Our case is remarkable for numerous reasons. He did not report a history of chronic sinusitis at the initial examination and, furthermore, there were no clinical or radiographic signs of maxillary sinusitis on the contralateral sinus. The time interval between acute sinusitis (purulent rhinorrhea and nasal obstruction) and symptoms of intracranial diseases, such as headache, altered mental status and lethargy, was of 2 days. It led us to believe that the sinusitis was of an acute type and was initiated by iatrogenic opening of an oroantral fistula (Figure 2).
The predisposition of young men to develop empyema has been explained by the high vascularity of the diploic system in this age group. Moreover, in our patient the absence of the spleen was probably a cofactor of the rapid development of the intracranial complication. Finally, the presence of the air content into subdural space is suspicious of the odontogenic anaerobic microflora that was founded at cultural examination after empyema evacuation and that represents an extremely rare report.
Radiological evaluation should be done in all patients in whom subdural empyema is suspected. Although magnetic resonance imaging (MRI) is more sensitive in showing parenchymal abnormalities such as abscess, cranial CT is often the first neuroimaging done in emergency and gold standard for visualization of the paranasal sinuses and associated bony abnormalities. In early cases of subdural empyema, CT might not show a fluid collection, so consideration should be given to repeated CT imaging or MRI as the clinical scenario dictates. As shown by our case, CT evidenced the empyema as a thin, hypodense subdural lesion, with linear enhancement of the medial surface (Figure 3a and b). The grey-matter/white-matter interface is displaced inwardly. Mass effect is generally caused by edema and ischemia rather than mass effect from the abscess. The edema can cause effacement of the basilar cisterns and flattening of the cortical sulci. The sinuses might appear opacified, with air-fluid levels and bony erosion evident in some cases, but a clinical report of air levels into subdural space is extremely rare.
According to our neurosurgeon's diagnosis, he did not undergo lumbar puncture because it is hazardous and contraindicated in patients with subdural empyema, particularly if mass effect is present on CT. In fact, the results are not specific and a neurological deterioration and transtentorial herniation after lumbar puncture are well described, and have led to death.
Various therapeutic measures include intravenous antibiotics, craniotomy drainage of intracranial abscess, and endoscopic and/or external drainage of affected sinuses. Once the diagnosis is made, the patient must undergo a combination of high-dose antimicrobial therapy that should be directed against the most common organisms and should include broad-spectrum activity against aerobic and anaerobic cocci and bacilli. Recommended empiric therapy is a third-generation cephalosporin plus metronidazole, which offers broad coverage and good cerebrospinal fluid and abscess penetration. In our case, according to our neurosurgeon, he was given vancomycin and metronidazole and the antibiotic regimen was modified after the culture reports with the adding of meropenem, which is the gold standard therapy in cases of Bacteroides. However, it is universally accepted that aggressive antibiotic therapy is not an alternative to surgical drainage that is recommended without delay. The goals of surgical intervention are both decompression of the brain and complete evacuation of purulence through craniotomy, and a definitive management of the infected sinuses should be done. The choice of surgical approach depends on the involved sinus and can include maxillary irrigation, external frontoethmoidectomy, sphenoid sinusotomy, antral washout, and frontal trephine. With the advent of endoscopy in treatment of sinusitis, the external approach has been less utilized; according to some authors, we adopted the external approach for a complete curettage of the maxillary sinus.