Neuroradiology Case of the Month

June 2002

Edward P. Lin, Manoj Ketkar, MD,
and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: A 94-year-old female presented with a one week history of diarrhea, vomiting, fever and mental status change. The patient was treated with antibiotics for two episodes of right otitis media, one month and three months prior to admission. The symptoms of headache and otalgia subsided after treatment on both occasions.

Radiologic Findings: CT of the head and temporal bone (Fig. 1) with contrast revealed: 1) a right otitis media with destruction of the right ossicles and involvement of the semi-circular canals, 2) a right purulent mastoiditis with erosion of the right petrous temporal bone and involvement of adjacent dura, and 3) an enhancing abscess measuring 2.7 x 1.7 cm in the right cerebellar hemisphere.

MRI of the head confirmed CT findings of right mastoiditis and a right cerebellar abscess with surrounding edema and mass effect on the fourth ventricle. The lesion exhibited low signal intensity on T1-weighted (Fig. 2) and high signal intensity on T2-weighted (Fig. 3) imaging. Diffusion-weighted imaging (Fig. 4) demonstrated an area of restricted diffusion in the right mastoid sinus and cerebellar hemisphere.

Diagnosis: Mastoiditis with Intracranial Abscess.

Figure 1: Post-contrast axial head CT demonstrates right mastoiditis (arrowhead) with erosion of the right petrous temporal bone (arrow) and involvement of adjacent dura. Ring enhancing lesion in the right cerebellar hemisphere measures 2.7 x 1.7 cm.	Figure 2: Post-contrast sagittal T1-weighted MR reveals hypointense lesion in the right cerebellar hemisphere with ring enhancement.
Figure 3: Axial T2-weighted image demonstrates high intensity signal in the right mastoid sinus and right cerebellar hemisphere with surrounding edema (arrowheads) and mass effect on the fourth ventricle (arrow).	Figure 4: Diffusion-weighted imaging shows an area of restricted diffusion in the right mastoid sinus and cerebellar hemisphere.

Discussion: Coalescent mastoiditis is a frequent complication of otitis media and usually occurs in pediatric populations [1,2]. It is defined as the inflammatory involvement and progressive resorption of the bony septae within the mastoid cavity [3-5]. Antibiotic compliance, bacterial susceptibility and immune status affect the course of disease [3]. When treatment of acute mastoiditis is not successful, intracranial or extracranial inflammatory complications may occur [3,4].

Intracranial complications include meningitis, encephalitis, brain abscesses, epidural abscesses, and lateral sinus thrombosis [4]. Intracranial complications of mastoiditis have decreased in incidence from 2.3% to 0.24% with the advent of antibiotic use [3,4]. The annual risk of intracranial complications in an adult with active chronic otitis media is 1 in 10,000 per year [4]. Complications most commonly involve Proteus, Pseudomonas or Staphylococcus [5].

Fever and otalgia are the most common presenting symptoms, but patients may also experience headache and altered mental status such as in this patient [3,5]. Symptoms of headache and altered mental status warrant radiological investigation of intracranial or extracranial complications.

CT can easily detect coalescent mastoiditis [5]. Diagnosis of coalescent mastoiditis can usually be determined by comparing the number, thickness and mineralization of mastoid intercellular trabeculae with the contralateral side [5]. The sensitivity of CT scanning in acute mastoiditis ranges from 87.2 to 100% [4].

CT and MR are equally capable of detecting a subperiosteal abscess, Bezold’s abscess and intracranial complications [5]. Intravenous contrast is generally recommended, as it allows better visualization of sinus thrombosis and abscess [3,5]. Purulent collections exhibit ring enhancement and changes in signal intensity on MRI [5]. MR venography with TOF technique can comfirm the diagnosis of a sinus thromobosis [5].

This patient was treated with triple antibiotic therapy. She and her family declined surgical treatment.

References:

1. Behrman. Nelson Textbook of Pediatrics. Saunders, 2000. pg.1957.
2. Juhl. Paul and Juhl's Essentials of Radiologic Imaging. Lippincott Williams & Wilkins, 1998. pg.1302.
3. Cynthia G, Bernstein J, Jong A, Sulek M, Friedman E. Intracranial Complications of Acute Mastoiditis. International Journal of Pediatric Otorhinolaryngology. 52(2): 143-148, 2000.
4. Spiegel JH, Lustig LR, Lee KC,. Murr AH, Schindler RA. Contemporary presentation and management of a spectrum of mastoid abscesses. Laryngoscope. 108(6):822-8, 1998.
5. Maroldi R, Farina D, Palvarini L, Marconi A, Gadola E, Menni K, Battaglia G. Computed tomography and magnetic resonance imaging of pathologic conditions of the middle ear. European Journal of Radiology. 40(2):78-93, 2001.