March 2004 Case of the Month

printer friendly version

History: 39 year old male with headaches for the past month, middle-ear infection last week, now complains of fever, facial pain, and intermittent double vision.

Compiled by: Steven R. Nudo, MD

Technical Factors: Long and short axis fat and water weighted sequences were performed.

Findings: Increased signal is demonstrated bilaterally within the mastoid air cells, more confluent on the right than on the left, consistent with mastoiditis (image 1).

Image #1

Within the right petrous apex is a 3 x 2 x 1.5cm lesion of fluid signal on the axial T2 weighted sequence (image 2) and isointense signal on the T1 pre-contrast sequence (images 3-5).


Image #2	Image #3

Image #4	Image #5

Thick, irregular rim enhancement is present on the post-contrast axial T1 weighted sequence (images 6-8), for which a petrous apex abscess is the primary diagnostic consideration.

Image #6

Image #7

Image #8

Also demonstrated is effacement of the right pre-pontine extra-axial space, moderate enhancement of the right 7th and 8th cranial nerves as well as their dura (image 7, yellow arrow). Effacement of the right 6th (image 8, yellow arrow) and right 5th (image 9, red arrow) cranial nerves is also demonstrated, however, these are not well seen due to the mass effect of the right petrous abscess. The normal left 5th cranial nerve is also noted for comparison (image 9, blue arrow).


Image #9	Image #10	Image #11

Meningeal enhancement of the medial right temporal lobe (images 10-12), anterior brainstem (image 13), and right tentorial enhancement (image 14) is also present. The left side of the brain demonstrates no abnormal leptomeningeal enhancement. No mass effect is noted involving the brainstem. The petrous portion of the right internal carotid artery is encased by this abscess. The flow void from the involved segment of the right ICA is well seen along the anterolateral aspect of the abscess on the coronal data sets (image 10, blue arrow). The mildly tortuous basilar artery is directly adjacent to the abscess, but is not encased.


Image #12	Image #13	Image #14

The optic nerve chiasm and tracts are normal and not involved. The superior margin of this petrous apex abscess abuts the right cavernous sinus. The abscess lies adjacent to the posteroinferior portion of Meckel’s Cave (image 9, yellow arrow). The 4th cranial nerves appear intact bilaterally.

Image #9

The orbits are unremarkable prior to, and after contrast augmentation. The clivus is intact. Prevertebral soft tissues are preserved. At the C3-C4 level, mild non-compressive spondylosis is noted. Incidental, millimeter-sized, linear vascular enhancement is noted in the right posterior parietal region, extending from the posterior horn of the lateral ventricle to the cortex (image 15), for which a venous angioma is favored. No evidence for hemosiderin deposition or gliosis in either portion of the brain.

Image #15

Mild left sphenoid sinusitis is apparent, along with left maxillary mucus retention cyst. Minimal ethmoid mucosal inflammation is demonstrated bilaterally. No vascular occlusion is apparent within the brain. Dural venous sinuses appear patent. The right jugular vein is patent.

Diagnosis: Gradenigo’s Syndrome

Discussion:
Gradenigo’s Syndrome consists of the clinical triad of purulent otomastoiditis, abducens (VI) nerve palsy, and deep facial/retro-orbital pain along the trigeminal (V) nerve distribution. The syndrome presumably stems from otomastoid infection, which then spreads to the petrous apex, leading to petrous apicitis. Pneumatization of the petrous air cells is necessary for the process to start. The abducens nerve travels in Dorello’s canal, which is immediately adjacent to the petrous apex (image 16).

Image #16

     The trigeminal nerve is affected by inflammatory extension to the gasserian ganglion, which lies within Meckel’s Cave, located anterosuperior to the petrous apex. An enhancing lesion in the petrous apex such as the one presented in this case, with the appropriate clinical history, is strongly suggestive of the syndrome.
     Once considered a common condition, petrous apicitis and Gradenigo’s Syndrome are now rarities in today’s antibiotic era. The organisms are typically pseudonomads, becoming trapped within the complex air cells of the petrous apex. Tuberculosis has also been documented as a rare etiology. If left untreated, the infection will progress to osteomyelitis in the surrounding bone. The proximity of the venous sinuses to the petrous apex accounts for the high incidence of venous sinus thrombosis. The etiology may also be due to a mechanical blockage from a mass lesion within the mastoids.
     CT scan is superior to MRI in assessing bony destruction/erosion, however MRI will better demonstrate extension of disease into the cisterns, internal auditory canal, or possible sequela such as arterial/venous thrombosis, abscess, and meningitis. Better visualization of the nerves is also an advantage of MRI.
     Treatment consists of antimicrobial therapy, usually directed towards pseudonomads. Surgical drainage may be indicated if patients fail to respond completely. Surgery is also warranted when patients have a mechanical obstruction or when complications develop such as abscess, thrombosis, or cranial nerve deficits. Post-operatively, adequate drainage should occur within several months. Resolution of cranial nerve palsies typically occurs over 3-4 weeks. Death was a common complication of Gradenigo’s Syndrome in the past. In today’s era of antibiotics and advanced surgical techniques, the survival rate has dramatically improved.

Sources:
Lustig LR: Skull Base, Petrous Apex, Infection. E Medicine, 2002.
Orrison WW., Neuroimaging. Pennsylvania: Saunders, 2000.
Atlas, SW., Magnetic Resonance Imaging of the Brain and Spine. Pennsylvania: Lippincott-Raven, 1996
Umansky F, Elidan J, Ala Rezo A., Dorello’s Canal: a microanatomical study. Medicosecuador