eMedicine Specialties > Radiology > Head/Neck
Temporal Bone, Acquired Cholesteatoma: Imaging
Updated: May 1, 2007
Radiography
Findings
Conventional temporal-bone projections remain in use in many parts of the world where CT scanning and MRI are not available. Standard projections for the temporal bone include the Law, Schuller, Mayer, Owen, Chausse III, transorbital, Stenvers, submentovertical, and Towne views. Schuller, Stenvers, Towne, and submentovertical projections are the most useful in the diagnosis of acquired cholesteatoma of the temporal bone.
The Schuller view is a lateral view of the mastoid, obtained with the sagittal plane of the skull parallel to the film and with 30º-cephalocaudal angulation on the radiographic beam. This view shows the degree and extent of mastoid pneumatization, the status of the trabecular pattern, and the position of the lateral sinus.
The Stenvers view is obtained with the patient facing the film and the head slightly flexed and rotated 45º toward the side opposite the examination. The radiographic beam is angulated 14º caudad. The long axis of the petrous pyramid is parallel to the plane of the film, and the entire pyramid, including its apex, is well visualized. This view shows the entire pyramid, arcuate eminence, internal auditory canal, porus acusticus, horizontal and vertical semicircular canals, vestibule, cochlea, mastoid antrum, and mastoid tip.
The submentovertical view (also termed axial or basal) is obtained from under the chin and has the advantage of showing both temporal bones on the same image. In this view, the external auditory canal, eustachian tube, middle ear (including the incus and the head of the malleus), mastoid air cells, styloid process, internal auditory canal, and petrous apex are visualized. This view also demonstrates the foramen ovale, foramen spinosum, and jugular foramen from the base of the skull.
The Towne view is an anteroposterior projection with a 30º tilt. As in the submentovertical view, it allows comparison of both petrous pyramids and mastoids in the same image. The petrous apex, internal auditory canals, arcuate eminence, mastoid antrum, and mastoid process can be identified clearly.
High-technology imaging modalities have become the radiologic methods of choice in the study of acquired temporal-bone cholesteatoma.
Degree of Confidence
Degree of confidence in radiography is low because of the complex anatomy of the temporal bone and the small radiologic changes induced by pathologic conditions. Interpretation of findings always depends on the experience of the physician.
False Positives/Negatives
The false-negative rate with plain radiographs is high.
Computed Tomography
Findings
CT-scanning technique
Direct thin-section CT scanning in axial and coronal planes is a must for optimal evaluation of temporal-bone anatomy and pathology. Axial images are obtained parallel to the infraorbitomeatal line to reduce the radiation dose to the lens of the eye. Direct coronal images can be obtained in supine hanging-head position or prone with the neck extended. Axial images should include the top of the petrous apex to the inferior tip of the mastoid, and coronal images should be obtained from the anterior margin of the petrous apex to the posterior margin of the mastoid.
Contiguous 1- to 1.5-mm-thick sections should be obtained by using conventional sequential acquisition. A spiral technique may be used if a pitch of 1:1 also is used. A small (12-cm) field of view can be applied with scans for each ear, reconstructed separately by using a bone algorithm. Intravenous contrast enhancement is usually not required. High-resolution CT scanning is ideal for the evaluation of middle-ear pathology. Contrast-enhanced CT scanning also is useful, if an intracranial complication is suspected and/or if a brain hernia (encephalocele) is present in the bed of the revision surgery.
Recent advanced technology, such as multidetector-row scanning with submillimeter (0.5-mm) section thickness and high-speed rotation (0.5 second per rotation), has reinforced the benefits of CT scanning in assessing temporal-bone cholesteatomas.
Applications of CT scanning
CT scanning offers high-resolution images with a section thickness of approximately 1 mm, which allows for good visualization of the bony, ossicular, and inner-ear anatomies. On CT scans, good contrast is demonstrated for bone, soft tissue, and air.
CT scanning is the preferred method for evaluating chronic middle-ear disease, including acquired cholesteatoma, because of its ability to demonstrate bony destruction.
CT scanning is used to establish the surgical procedure needed in each patient. CT scanning helps to determine the extent of the cholesteatoma; the location and size of the sac; the status of the ossicular chain; the integrity of the facial canal, tegmen, and sinus plate; and the position of the dura, sigmoid sinus, and jugular bulb.
CT-scan findings
CT-scan findings in acquired temporal-bone cholesteatoma are characterized by a soft-tissue homogeneous mass with focal bone destruction. Cholesteatoma almost always presents as a complication of chronic otitis media; therefore, the middle-ear space appears cloudy as a result of granulation tissue, pus, and fluid.
Liu and Bergeron have proposed the following CT-scan findings in cholesteatoma:4
- Erosion and destruction of the lateral wall of the attic (scutum)
- Widening of the aditus ad antrum
- Displacement of the ossicular chain
- Destruction of the ossicles
- Labyrinthine fistula
- Erosion of the facial canal
- Dehiscence of the tympanic roof (tegmen tympani)
- Destruction of the mastoid (automastoidectomy cavity)
- Dehiscence of the sigmoid plate
- Erosion of the roof of the external auditory canal (posterosuperior wall)
Degree of Confidence
CT scanning is considerably more sensitive than conventional radiography for detecting cholesteatomas.
False Positives/Negatives
Granulation tissue and a chronically infected middle-ear mucosa are almost impossible to differentiate from a cholesteatoma.
Magnetic Resonance Imaging
Findings
MRI technique
Optimal MRI technique depends on the clinical situation and age of the patient. High - field-strength, contrast-enhanced imaging in the axial and coronal plane has been considered the criterion standard for evaluation of the internal auditory canal (IAC) and inner-ear structures. Nonenhanced and gadolinium-contrast-enhanced T1-weighted images are compared in order to differentiate bright lesions (fat and blood products) from enhancing lesions visualized after contrast infusion. Three-dimensional (3D) fast spin-echo T2-weighted images allow high-resolution imaging of the IAC and labyrinth. A variety of 3D gradient-echo techniques with thin sections also are available.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after they were given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of theeyes;jointstiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Applications of MRI
The role of MRI in the evaluation of middle-ear pathology is limited. The most important contributions of MRI to the study of acquired temporal-bone cholesteatoma are the following:
- MRI can precisely define the borders of large lesions.
- MRI can depict the relationship of the lesion to intracranial structures.
- MRI helps in evaluating intratemporal and extratemporal complications.
- Follow-up of patients who have undergone middle-ear surgery for a cholesteatoma
MRI defines the integrity of the dura, which is best appreciated with T2-weighted sequences, without the need for contrast material. However, in cases of dural infection, subtle contrast enhancement may be the only clue that dural involvement is present.
MRI delineates intracranial extension of the cholesteatoma or protrusion of the intracranial contents into the middle ear, when defects of the tegmen tympani or sinus plate are visualized on the CT scan. MRI is also indicated when the facial nerve is involved.
MRI findings
Acquired cholesteatomas generally produce low signal intensity on T1-weighted images, with no change after contrast administration, and high signal intensity on T2-weighted images.
MRI is also used to differentiate cholesteatomas from other temporal-bone lesions, such as cholesterol granulomas, granulation tissue, inflammatory mucosa, and scar tissue.
Cholesterol granulomas produce high signal intensity on both sequences, with no contrast enhancement. Granulation tissue and inflammatory mucosa generally produce a hypointense or intermediate signal on T1-weighted images and a hyperintense signal on T2-weighted images with contrast enhancement. Because of its fibrous nature and, possibly, the microvascular thrombosis phenomenon, it is necessary to obtain delayed contrast-enhanced images with a delay of 30–45 minutes after contrast-material administration.
Organized scar tissue produces a hypointense intermediate signal on T1- and T2-weighted images with no contrast enhancement.
A study by Frederique Dubrulle shows the reliability of diffusion-weighted fast spin-echo MR imaging in the detection of recurrent cholesteatoma in patients who have undergone middle-ear surgery.5 Recurrent cholesteatoma was diagnosed if the lesion had low signal intensity on unenhanced T1-weighted images, showed no change in signal intensity on delayed contrast-enhanced T1-weighted images, and had high signal intensity on diffusion-weighted images obtained with a b factor of 800 sec/mm2.
The negative predictive value was 100%, which means that patients who show no signs of recurrent cholesteatoma on diffusion-weighted fast spin-echo images may not need second-look surgery
Degree of Confidence
MRI is considerably more sensitive than conventional radiography, but it is less sensitive than high-resolution CT scanning, because of the lack of bone delineation on MRI.
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Further Reading
Keywords
keratoma, congenital cholesteatoma, primary acquired cholesteatoma
