When Occam's razor loses its edge: the simplest explanation isn't always correct

Facial infections are common in children.¹ The axiom ‘facial infection is odontogenic in origin until proven otherwise’ is often used in medicine.² The symptoms of a dental abscess include pain in the affected tooth or region, redness and swelling in the face, a tender, discoloured or loose tooth, sensitivity to hot or cold, and halitosis. If the infection spreads systemically, fever and malaise may arise. In severe cases, patients can experience trismus, dysphagia or dyspnoea.³ Early diagnosis and treatment is therefore essential when managing such facial infections owing to the possibility of sepsis or spread to adjacent structures.⁴ Rare, but potentially fatal results of such spread are intracranial suppurative lesions, which can be difficult to diagnose, and can result in serious long-term morbidity if not managed promptly and appropriately.⁵ For this reason, a high index of suspicion is required if neurological deterioration occurs. Subdural empyema (SDE) accounts for over 20% of intracranial abscesses⁶ and occurs when pus collects between the outermost layer of meninges, the dura mater and the arachnoid mater. Signs and symptoms of SDE include fever, headache, confusion or drowsiness, nausea or vomiting, hemiparesis or hemiplegia, seizure, and a recent history of facial infection, surgery or trauma.⁶

Subdural empyema is a rare condition, with one study of a low socio-economic demographic finding an incidence of one case per 193,000 people per annum.⁷ The incidence is suggested to be even lower in more developed regions.⁸

The primary causes of intracranial SDE are typically sinonasal inflammatory disorders,⁹ rather than odontogenic sources. One large study (n=699), showed paranasal sinusitis to be by far the most common cause (67.1%), with other significant sources including meningitis (10.4%), otogenic causes (9.2%) and trauma (8.2%). Notably, dental caries accounted for only 0.7% of SDE cases.⁷

An intracranial abscess occurs through direct or indirect spread of infection. Direct spread occurs following the erosion of sinus wall. However, indirect spread is more common, occurring through retrograde thrombophlebitis of the ophthalmic and facial veins. As these veins are valveless, thrombophlebitis can communicate with the cavernous sinus and other dural venous sinuses.¹⁰

Odontogenic infections and sinusitis may present clinically with similar symptoms. These include pain, swelling and facial tenderness, with the source being adjacent anatomically. With this in mind, sinusitis is only diagnosed once dental sources of infection have been eliminated. Frequently, when there is an obvious dental cause identified by plain radiography, the search for other causes is suspended. In this case, both odontogenic and sinogenic pathological processes were concurrently present, leading to a delayed diagnosis of sinusitis, which was not suspected until the more insidious SDE manifested.

Case presentation

A male patient, aged 11, reported to the accident and emergency department with a chief complaint of right-sided facial pain and swelling with increased jaw pain and associated trismus. The patient also had a 2-day history of loose stools and tiredness, with a vomiting bug 1 week previously.

On examination, a right-sided facial swelling was present, which was tender to palpate. This swelling extended from the right pre-auricular area to the right neck, which was also tender to palpate. The upper right first molar (UR6) was heavily broken down and tender to percuss, with an associated mild buccal swelling. The lower right first molar (LR6) was also heavily decayed, although not painful. The patient had generalized poor oral hygiene. A dental panoramic tomograph (DPT) revealed a grossly carious UR6 with peri-apical radiolucency, in addition to a carious LR6 (Figure 1). On admission, the patient's paediatric early warning score (PEWS) was measured at 1 owing to a temperature of 37.9°C, indicating that the patient was systemically unwell and would require regular observation at 4-hourly intervals. PEWS is a scoring system used in hospitals for the early recognition and prediction of deterioration in children through regular checking of their vital signs.¹¹ The patient was immediately started on intravenous co-amoxiclav and metronidazole, with an agreed plan to extract the UR6, and balance by extracting the deeply carious LR6, the next morning in theatre.

The next morning, the patient displayed signs of confusion, tailing off midway through his sentences, and exhibiting delayed response times to commands. He also had a mild right-sided ptosis. His blood results showed an elevated white cell count and raised inflammatory markers. Owing to his deteriorating neurological state, an MRI and CT venogram were taken. The MRI (Figure 2) and CT scan showed base-of-skull collection, left extra-axial collection, and pterygoid collection. The CT scan also showed marked sinusitis involving the maxillary, ethmoid, frontal and sphenoid sinuses (Figure 3).

Treatment

Once the SDE was discovered, cefotaxime was added to the antibiotic regimen. The patient was transferred to theatre under the care of neurosurgery, with ear nose throat (ENT) and oral and maxillofacial surgery input.

On examination, intra-orally, his floor of mouth, buccal tissues and soft palate were normal. The right neck and sub-mandibular region were soft, and the patient had normal mouth opening. The UR6 and LR6 were removed intact, with no purulent discharge from either socket. There was an apical granuloma attached to the root of the UR6. The UR6 socket was swabbed and sent for culture and sensitivity tests. The ENT examination found a grossly engorged and inflamed nasal airway, congested middle meati, and inflamed adenoidal pad. The nose was suctioned, and the middle turbinates were medialized. An uncinectomy and middle meatal antrostomy were performed, and pus samples were sent for microbiology.

Pathology specimens were sent of the right and left middle meatus. The features were of non-specific chronic inflammation. The inflammatory change was more prominent in the left specimen. The culture and sensitivity results showed that the swab of the UR6 socket isolated a large number of yeasts. The sample abscess fluid from the ENT procedure grew large numbers of Streptococcus intermedius and Haemophilus influenza.

Two days later, the patient had a focal seizure, which resulted in right-armed weakness. He was returned to theatre where a left fronto-temporo-parietal craniotomy was carried out by the neurosurgery team. A subdural empyema evacuation was performed, and a subgaleal drain was placed. Diffuse cerebritis was evident during the procedure. Despite these efforts, the next day, the patient was clinically fluctuating. An updated cranial CT demonstrated further midline shift, mass effect and extradural haematoma. The patient was taken back to theatre for further craniotomy and washout. Samples taken were sent for culture and sensitivity analysis, which reported moderate growth of Gram-positive cocci. Unlike the intra-oral extraction socket swab, no yeasts were cultured from the craniotomy sample.

After this, the patient completed a 9-week course of daily intravenous antibiotics and undertook rehabilitation through speech and language therapy, physiotherapy, and occupational therapy for a number of months. The MRI that was taken 4 months after his procedure showed no active areas of ongoing infection. A defect-restoring cranioplasty was performed 4 months after his initial presentation using the stored bone flap from his previous surgery. The patient required long-term neurorehabilitation follow up, although he gradually improving back to his premorbid condition with regards to speech and mobility.

Discussion

In the past, SDE was regarded as a fatal condition, with mortality rates quoted as 100% until the advent of the antibiotic era.⁶ Today, SDE remains a dangerous condition, with studies reporting significant morbidity¹² and a mortality rate of approximately 10–40%.¹³ Common residual effects include epilepsy, hemiparesis and other neurological disorders.^7,10

Such infections are often polymicrobial. Cultures taken from SDE commonly produce aerobic and anaerobic streptococci. Staphylococci are found less commonly, as are aerobic Gram-negative bacilli and non-streptococcal anaerobes.^10,13 Organisms isolated from cases of SDE secondary to sinusitis are typically from the Streptococcus milleri family (Streptococcus anginosus, Streptococcus intermedius, and Streptococcus constellatus), or, less commonly, the Haemophilus species or Bacteroides species. In this case, large numbers of Streptococcus intermedius and Haemophilus influenza were isolated from the sample of pus taken during the uncinectomy. Large numbers of yeasts were isolated from the extraction socket, which could indicate that there was an underlying immunocompromised state, or simply have been a link to the carious status of his teeth.¹⁴

Owing to the potentially severe outcomes of intracranial suppuration, early intervention and treatment are crucial. In this case, the patient presented with classical symptoms of a dental abscess, including facial swelling, trismus, temperature, and elevated inflammatory markers and white blood cell count, masking a more serious condition, which subsequently manifested itself clinically as neurological deterioration, confirmed by CT and MRI scanning. This imaging was crucial, because it made apparent the extent of the sinusitis, which had not been evident with the DPT alone.

Although rare,⁷ subdural empyema can be caused by an odontogenic abscess,^15–17 but this is not thought be likely in this case for a number of reasons:

• On extraction, the UR6 had an attached apical granuloma, with no pus extruding from the socket, implying chronic rather than acute infection. In addition, swabs of the socket, when sent for culture and sensitivity analysis, resulted only in growth of yeasts rather than bacterial micro-organisms.
• There was no communication evident clinically between the socket of the UR6 and the maxillary sinus. As well as this, the root of UR6 and associated apical granuloma were shown to be encapsulated in bone on the CT scan. There was no breach evident into the maxillary sinus.
• The UR6 is unlikely to have caused a left-sided collection due to their relative anatomical positions. In addition, bilateral sinusitis is evident on the CT, which seemed to be worse on the left side.

With this in mind, we suspect that two coinciding conditions were present, with the dental abscess overshadowing the sinusitis initially. In hindsight, the patient's history of a ‘vomiting bug’ the week before, an episode of vomiting on the day of presentation, and recent tiredness, may have been indicators of a more sinister infection. However, these were not thought to be linked to the presenting symptoms initially. This case shows the importance for dentists to understand the need for early recognition of neurological symptoms and the associated link to a more sinister condition.

In particular, it highlights the role of measuring a patient's temperature and carrying out a simplified neurological exam, if possible, as a screening tool for patients presenting with a history of nausea, vomiting or lethargy coexisting with their primary complaint. This may detect subtle signs of intracranial spread of infection and would indicate that medical assessment of the patient is required urgently. The acronym AVPU (alert, voice, pain, unresponsive) is a simplified neurological assessment to assess impaired consciousness in patients. It is a tool that dentists should use in cases of suspected neurological deterioration, where eye, voice and motor responses are taken into consideration. If the response is below ‘alert’ then a medical assessment is required.¹⁸

Conclusion

In summary, a seemingly obvious minor dental infection marked a hidden sinusitis that resulted in a subdural empyema. This 11-year-old child required extractions, uncinectomy, middle meatal antrostomy and washout of sinuses under general anaesthetic, followed by a craniotomy and a second wash out of the intracranial collection. The patient also required a 9-week course of intravenous antibiotics, as well as an extensive and ongoing period of rehabilitation. This case serves as a reminder to dentists that progressive neurological symptoms can be indicative of intracranial pathology, and that these patients should be promptly referred to an accident and emergency department for assessment. Although Occam's razor can often be used to focus on simple explanations as ‘common things occur commonly’, this case shows the importance of considering all of the differential diagnoses.