Subdural Empyema (SDE) is a condition that can complicate diseases of the Ear, Nose and Throat (ENT) system or immunodepression. In Western countries, SDE is a rare condition, affecting approximately 5 patients/million population/year . Due to its low incidence, PDS is often not recognised by emergency or outpatient departments, and its severity may be underestimated. A brain scan with contrast injection is requested as a first line of defence and MRI is used to confirm the diagnosis.
We report the case of a 22-year-old patient who presented to the emergency department with frontal headache associated with a purulent nasal discharge. The brain scan showed maxillary, ethmoidal and left frontal sinus filling on bone reconstruction (Figure 1,2 and 3), and the brain parenchyma slices showed́ a left frontal extra axial collection (Figure 4).
Figure 1, 2 and 3: Axial cross-sectional CT scan of the brain in the bone window showing the filling of the maxillary, ethmoidal and left frontal sinuses respectively.
The diagnosis of SDE was evoked and then confirmed by injected brain MRI which individualized a left frontal extra axial collection in T1 iso signal (Figure 5), Flair, diffusion hypersignal (Figure 6) with ADC restriction (Figure 7), enhanced peripherally after gadolinium injection (Figure 5) and a maxillary, ethmoidal and left frontal sinus filling in T2 hypersignal, enhanced peripherally after PDC injection (Figure 8, 9 and 10).
Figure 4: Cerebral CT axial section in parenchymal window illustrating a left frontal extra axial collection.
Figure 5: Brain MRI in axial section illustrating a left frontal extra axial collection in T1 iso signal enhanced in the periphery after gadolinium injection.
Figure 6: Brain MRI in axial section showing a left frontal extra axial collection in diffusion hypersignal.
Figure 7: Brain MRI axial slice showing a frontal extra axial collection with restriction on the ADC sequence.
Figure 8, 9 and 10: Axial slice brain MRI showing maxillary, ethmoidal and left frontal sinus filling in T2 hypersignal, peripherally enhanced after PDC injection respectively.
Any clinical suspicion of SDE should lead to urgent contrast-injected brain imaging. Brain CT shows subdural hypodensity (Figure 4), enhanced by peripheral contrast corresponding to the empyema wall . The mass effect on the parenchyma may be greater than the volume of the collection itself, due to perilesional oedema that may reflect an inflammatory reaction to the SDE, pre suppurative contact encephalitis or cortical venous thrombosis . Magnetic resonance imaging allows better visualization of the SDE, and the diffusion sequence confirms the infectious origin of the subdural collection, which appears hyperintense  (Figure 5).
Thus, as soon as the diagnosis is radiologically confirmed, or even suspected, contact must be made without delay with a neurosurgical department in order to organize emergency treatment in a neurosurgical environment.
PDS is an absolute neurosurgical emergency. Any delay in diagnostic and/or therapeutic management exposes the patient to an increased risk of death or neurological sequelae. CT and MRI cross-sectional imaging with injection of contrast medium allows the diagnosis to be made.