Neuroradiology (1992) 34:494-496

Neuro--

radiology 9 Springer-Verlag 1992

Contrast-enhanced magnetic resonance imaging of sub- and epidural empyemas K. Tsuchiya 1, K. Makita 1, S. Furui 1, S. Kusano 1, and Y. Inoue 2 1Department of Radiology, National Defense Medical College, Tokorozawa, Saitama, Japan 2Department of Radiology, Mitsui Memorial Hospital, Tokyo, Japan

Smnmary. Contrast-enhanced magnetic resonance images (MRI) of three patients with subdural (SDE) and two with epidural empyemas ( E D E ) were reviewed. In each case, the capsule of the lesion demonstrated enhancement, and distinction between capsule and contents was obvious on contrast-enhanced images. In SDE, contrastenhanced images clearly depicted thickening of the neighbouring dura mater and a co-existent brain abscess. In E D E , part of the displaced dura mater did not enhance, which facilitated differentiation from SDE. Contrastenhanced M R / w a s thus of value in diagnosis.

Key words: Subdural empyema-Epidural empyema Gadopentetate dimeglumine - Magnetic resonance imaging Subdural empyema (SDE) and epiduralempyema ( E D E ) are relatively rare, accounting for 26-32 % of intracranial infections [1, 2]. Several workers have emphasized the sensitivity of M R I in demonstrating these lesions, which computed tomography (CT) not infrequently fails to reveal [3-5]. The purpose of this study was to assess the value of contrast-enhanced MRI.

Materials and methods MRI studies of three patients with SDE and two with EDE, three males and two females ranging in age from 14 to 70 years (mean: 38.8 years), were reviewed. The diagnosis was proved surgically in four patients, and established on the basis of response to antibiotics in one. MRI was performed at either 1.0T (one patient with SDE) or 1.5T (the other four patients). In addition to Tl-weighted [500600/22-30 (TR/TE)] and T2-weighted (2500/90-100) spin-echo images, contrast-enhanced Tl-weighted images were obtained after IV gadopentetate dimeglumine (0.1 mmol/kg).

Results Two of the three patients with SDE had a facial wound as the source of infection, while the two with E D E had head trauma. In the four surgically treated patients, the cau-

sative organisms were identified (they were Peptostreptococcus, Streptococcus mirelli, Staphylococcus aureus and Pseudornonas aeruginosa). All patients with SDE also had an abscess in the neighbouring brain, while both patients with E D E also had subcutaneous abscesses. In both SDE and E D E , the pus in the lesion was hypointense relative to the cortex and hyperintense to cerebrospinal fluid on Tl-weighted images (TlWI). The contents were hyperintense to cortex on T2-weighted images (T2WI). On contrast-enhanced T l W I , the contents showed no enhancement. The SDE capsule was hypointense in two patients and isointense in one on T1WI, and hyperintense in two and isointense in one on T2WI. The E D E capsule showed hypointensity on T l W I in one patient and a mixture of hyper- and hypointensity in the other. On T2WI, the pattern of relative intensities was similar. All the capsules showed enhancement on contrastenhanced T l W I (Figs. 1-3). In addition, in patients with SDE, contrast-enhanced images clearly demonstrated thickening of the neighbouring dura mater and showed the adjacent brain abscess (Fig. 2). In patients with E D E , part of the displaced dura mater did not enhance, remaining hypointense. In one patient with E D E , contrast-enhanced T1WI revealed multiple septum-like structures within the lesion, which proved at operation to be granulation tissue (Fig. 3).

Discussion SDE and E D E are known to have three main causes: sinusitis and/or mastoiditis, surgery and trauma [4]. The first type frequently has a fulminant course, as it results from retrograde thrombophlebitis which progresses rapidly to the cortical veins, with consequent cerebral o e d e m a and infarction [6, 7]. In contrast, postoperative and traumatic empyemas tend to develop months or years after the original insult and follow a more benign clinical course [8, 9]. The MRI findings in SDE and E D E were initially reported prior to the introduction of gadopentetate dime-

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Fig. la-d. A 70-year-old woman with a subdural empyema (SDE) of unknown origin, a TIWI (SE 600/25) shows a slightly hypointense mass in the left temporo-occipital region, also shown on T2WI (SE 2500/100) (b). c,d Axial (SE 600/25, c) and coronal (SE 500/25, d) contrast-enhanced TIWI clearly show its outline and location Fig.2a-c. A 14-year-old boy with an SDE secondary to a facial wound, a,b TlWI (SE 500/30) and T2WI (SE 2500/100) show a right temporal SDE, hypointense on TlWI and hyperintense on T2WI. An abscess can be seen in the right frontal lobe. c Contrast-

enhanced TIWI (SE 500/30) shows enhancement of the capsule of both lesions. Thickening of the dura mater adjacent to the SDE is also demonstrated

Fig.3a-d. A 35-year-old man with a postoperative epidural empyema (EDE) (cranioplasty for skull fracture 2 years previously) a,b TlWI (SE 600/25) and T2WI (SE 2500/100) show a large EDE, separated from the brain by a hypointense rim. A small subcuta-

neous collection is present, c, d Axial (SE600/25) and coronal (SE 500/25) contrast-enhanced TIWI show enhancement of the capsule, but the deep part of the hypointense rim does not enhance. Multiple septa proved at operation to be ganulation tissue

glumine [3-5], and the unenhanced images in our patients were consistent with the previous descriptions. The presence and the extent of the lesions can be appreciated readily on MRI, which can also differentiate t h e m from sterile effusions and h a e m a t o m a s on the basis of differences in signal intensity. E D E s show a hypointense rim, which has b e e n ascribed to the displaced dura m a t e r [3, 5], and this was also noted in our patients. Contrast enhancement of the capsule was demonstrated in both types of lesion, enabling distinction between the abscess fluid and the capsule, not necessarily possible on unenhanced images. Similar rim-like enhancement has been described on CT in both types of

lesion [1, 4-8, 10-14]. Because enhancement reflects encapsulation of portions of the e m p y e m a , as described in several reports on S D E [8, 11, 13], it may not be demonstrated in the very acute phase, especially in E N T cases [4]. In the patients with SDE, enhancement of the thickened neighbouring dura mater, contiguous with the outer capsule of the e m p y e m a , was also demonstrated. This finding, as well as the hypointense rim of the E D E , allowed the precise localization of the empyema. The deep margin of the E D E s remained hypointense on contrast-enhanced images, which m a y m e a n that the dura m a t e r was not completely involved because of its resistance to inflammation. Furthermore, contrast-enhanced

496 i m a g e s r e v e a l e d a b r a i n abscess co-existing with t h e S D E , as s h o w n in o u r p a t i e n t s , a finding o f i m p o r t a n c e for e s t a b lishing t h e c o r r e c t surgical p r o c e d u r e .

References 1. Dazinger A, Price H, Schechter MM (1980) An analysis of 113 intracranial infections. Neuroradiology 19:31-34 2. Blaquihre RM (1983) The computed tomographic appearances of intra- and extracerebral abscess. Br J Radio156:171-181 3. Weingarten K, Zimmerman RD, Becker RD, Heier LA, Haimes AB, Deck IVLDF(1989) Subdural and epidural empyemas: MR imaging. AJNR 10:81-87 4. Moseley W, Kendall BE (1984) Radiology of intracranial empyemas, with special reference to computed tomography. Neuroradiology 26:333-345 5. Sze G, Zimmerman RD (1988) The magnetic resonance imaging of infections and inflammatory diseases. Radiol Clin North Am 26:83%859 6. Joubert MJ, Stephanov S (1977) Computed tomography and surgical treatment in intracranial suppuration. Report of 30 consecutive unselected cases of brain abscess and subdural empyema. J Neurosurg 47:73-78

7. Scharif HS. Ibrahim A (1982) Intracranial epidural abscess. Br J Radio155: 81-84 8. Luken MG, Whelan MA (I980) Recent diagnostic experience with subdural empyema. J Neurosurg 52:764771 9. Post EM. Modesti LM (1981) "Subacute" postoperative subdural empyema. J Neurosurg 55:761-765 10. Lott T. E1 Gammal T. Dasilva R, Hanks D, Reynold J (1977) Evaluation of brain and epidural abscesses by computed tomography. Radiology 122:371-376 11. Sadhu VK. Handel SF. Pinto RS. Glass TF (1977) Neuroradiologic diagnosis of subdural empyema and CT limitations. AJNR 1:39-44 12. Dunker RO. Khakoo R A (1981) Failure of computed tomographic scanning to demonstrate subdural empyema. JAMA 246:1116-1118 13. Zimmerman RD. Leeds NE, Danziger A (1984) Subdural empyema: CT findings. Radiology 150:417-422 14. Weisberg L (1986) Subdural empyema. Clinical and computed tomographic correlation. Arch Neuro143:497-500

K. Tsuchiya, M.D. Department of Radiology National Defense Medical College 3-2, Namiki, Tokorozawa Saitama 359, Japan

Contrast-enhanced magnetic resonance imaging of sub- and epidural empyemas.

Contrast-enhanced magnetic resonance images (MRI) of three patients with subdural (SDE) and two with epidural empyemas (EDE) were reviewed. In each ca...
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