Subdural empyema in acute sinusitis: The central role of imaging in the diagnostic management

A 10-year-old female presented to the Emergency Department following 3 days of high-grade fever, fronto-temporal headaches and vomiting. Neurological examination demonstrated right lower limb reduced power, postnasal drip, and pain on palpation over the frontal sinuses. The CRP was 255 and the WCC was 17.2.

A non-contrast CT (NCCT) of the head and sinuses demonstrated confluent opacification of the right maxillary, right ethmoid and right frontal sinuses indicative of sinusitis.

The patient later developed worsening neurological deficits. An MRI of the head showed a left para-median shallow fluid collection extending anteroposteriorly along the falx cerebri to the superior surface of the left tentorium cerebelli and appeared contiguous with the right frontal sinus. There was enhancement of the dura along the fluid collection after gadolinium administration. Corresponding restricted diffusion was seen on diffusion-weighted imaging (DWI)/ apparent diffusion coefficient (ADC) sequences within the fluid collection seen tracking along the bilateral frontal and left para-median regions. Overall appearances were suggestive of bilateral frontal and left para-median subdural empyema secondary to sinusitis.

Retrospective review of the initial NCCT demonstrated a subtle shallow left para-median collection tracking anteroposteriorly alongside the falx cerebri which was missed on the initial report.

Background

Sinusitis, or rhinosinusitis, is defined as symptomatic inflammation of the paranasal sinuses and nasal cavity mucosa.[1] The current preferred term is rhinosinusitis, given sinusitis occurs concurrently with nasal airway inflammation in the vast majority of cases.[2] Persistence of symptoms beyond 12 weeks constitutes a chronic diagnosis. Acute rhinosinusitis (ARS) is one of the commonest conditions seen in primary care[3] and in children[4]. ARS has several causes, the most common of which is a viral upper respiratory tract infection. 5-10% of patients with viral sinusitis have bacterial superinfection requiring antimicrobial treatment[5]. Intracranial complications of rhinosinusitis are true medical and neurosurgical emergencies[6].

Pathophysiology

Subdural empyema is defined by the accumulation of frank pus in the subdural space. Subdural empyema comprises 15-20% of focal bacterial infections of the CNS[7] and is a rare complication of ARS.[8] The clinical deterioration in subdural empyema is due to toxins that result from bacterial metabolism and can affect neural and glial function directly.[9] Of the possible suppurative intracranial complications, subdural empyemas have the worst outcomes.[8]

Clinical perspective

The mortality rate for subdural empyema is approximately 4% and morbidity includes hemiparesis in 15-35% of patients.[9][10] The documented presentation includes the rapid development of stupor, nuchal rigidity, seizures and hemiparesis, although this can vary.[11] In this case the patient developed right hemiparesis, seizures, photophobia and neck stiffness.

Imaging perspective

CT of the head remains a first-line investigation of neurological deficits in the acute setting due to its ease of access and availability. It may reveal oedema or mass effect[8]. However, MRI with gadolinium is the superior diagnostic modality for establishing the presence and extent of subdural empyema. MRI-DWI can be useful in delineating a subdural empyema from more superficial epidural space infections due to the bright signal seen in MRI-DWI.[12]

Outcome

The patient was transferred to a tertiary neurosurgical centre, undergoing an emergency craniotomy and treatment with antibiotics and anti-epileptics.

Take-home messages

• It is critical to look for subdural fluid collections on NCCT in patients with ARS especially if the frontal sinus is involved.
• Missing a diagnosis of subdural empyema is a life-altering event and potentially fatal.
• MRI is the gold standard in suspected subdural empyema. If CT is reported normal in the context of neurology, a reassessment of imaging needs to be made and MRI must be considered.

Written informed patient consent for publication has been obtained.