Neuroradiology Case of the Week

Case 28

Mayumi Oka, MD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 9-year-old male presented to the ED with headache, fever, right eye edema, and chemosis. CT of the sinus and orbit was requested.

Radiological Findings: Coronal CT demonstrated opacification of bilateral maxillary, ethmoid, sphenoid and frontal sinuses (Fig.1). There is a fluid collection with enhancing margin in the superior right orbit displacing the globe (Fig. 2). Another lentiform fluid collection is seen in the right frontal region (Fig. 3).
   MRI performed later in the day showed right epidural (Fig. 4), left subdural (Fig. 5) and right orbital fluid collections (Fig. 6), which demonstrated bright signals on diffusion-weighted images (Fig. 7A-C).

Figure 1	Figure 2
Figure 3
Figure 4	Figure 5
Figure 6
Figure 7A	Figure 7B
Figure 7C

Diagnosis: Intracranial empyema (right frontal epidural and left subdural) and right orbital abscess secondary to paranasal sinusitis.

Discussion:
   Subdural empyema (SDE) accounts for approximately 20% of intracranial infections, whereas epidural empyema (EDE) is uncommon and accounts for less than 5% of intracranial infections. In 65 to 90% of cases they are secondary to otorhinologic infections. Infection can spread intracranially directly from the sinuses through the cranium and dura, or by retrograde thromphlebitis via bridging emissary veins. Other causes include head trauma, neurosurgical procedures, and less commonly septicemia.
   SDE can be lentiform or crescentic in shape, and EDE is usually lentiform. When a hypointense margin is visualized on both T1- and T2-weighted images (displaced dura), one can diagnose EDE.
   MR imaging is superior to CT in delineating small SDE (paratentorial or subtemporal) using sagittal and coronal planes and detecting possible complications, such as cranial osteomyelitis, venous sinus thrombosis, purulent leptomeningitis and intracranial abscesses.

References:

1. Hansman Whiteman ML, Bowen BC, Post MJD, Bell MD. Intracranial infection, Chap. 21, In: Atlas SW. Magnetic Resonance Imaging of the Brain and Spine. Vol. 1 3rd ed. Philadelphia, LWW.
2. Subdural empyema, Dawodu ST, eMedicine. http://www.emedicine.com.