Introduction

MR imaging has an additional value in the detection and delineation of congenital temporal bone and acquired middle ear cholesteatoma. The combination of standard MRI sequences with intravenous gadolinium administration and Spin Echo Echo Planar Diffusion-Weighted (SE EPI DWI) images seems to have – up until now – the highest sensitivity. However SE EPI DWI still has major limitations due to susceptibility- related artefacts, relatively thick slices and low spatial resolution. We report our first experience with a singleshot Turbo Spin Echo diffusion-weighted imaging (single-shot TSE DWI) sequence for the detection and delineation of middle ear cholesteatoma, as well as congenital cholesteatoma, primary acquired cholesteatoma and pre-second look residual cholesteatoma.

MRI Protocol

The protocol for imaging cholesteatoma in our institution consists of 5 sequences. Images are acquired 45 minutes after the intravenous administration of gadolinium on a MAGNETOM Avanto using the standard Head Matrix coil and 2 locally built 7 cm surface ring coils, each connected via its own flex interface. The main difference between SE EPI DWI and single-shot TSE DWI is that the latter sequence uses a 180° RF refocusing pulse for each measured echo.

Case Report 1

13-year-old girl presenting with a small epitympanic congenital cholesteatoma at otoscopy.

Fig. 1A  Transverse and coronal high resolution CT image shows a small soft tissue lesion adjacent to the neck of the hammer suggestive of a small cholesteatoma (arrows). The intact tympanic membrane and the lack of chronic inflammatory alterations in the middle ear suggest a small congenital cholesteatoma (size 2 to 3 mm).

Fig. 1B  Coronal T2-weighted imaging (T2-WI) shows a small hyperintense nodular lesion in the signal loss region of the temporal bone (arrow). When comparing to Figure 1a the small hyperintense nodular lesions present the small congenital cholesteatoma

Fig. 1C  Coronal T1-weighted imaging (T1-WI) shows a small nodular lesion in the temporal bone corresponding to the small congenital cholesteatoma (arrow).

Fig. 1D  Coronal single-shot Turbo Spin Echo Diffusion- weighted imaging (TSE DWI) clearly shows the small hyperintensity in the temporal bone corresponding to the small congenital cholesteatoma (arrow).

Case Report 2

76-year-old male with chronic ear discharge.

Fig. 2A  Transverse high resolution CT image shows soft tissue in the attic (arrows) with ossicular erosion and disruption of the anterior part of the lateral semicircular canal (arrowhead).

Fig. 2B  Coronal reformation of a transverse multi slice data set clearly shows the lesion in the attic (large arrow) with suspected erosion of the tegmen (small arrow) and the lateral semicircular canal (arrow-head).

Fig. 2C  Coronal TSE T2-WI through the temporal bone at the level of the lateral semicircular canal clearly shows the slightly hyperintense cholesteatoma (arrows) surrounded by hyperintense fluid (arrowheads).

Fig. 2D  Coronal TSE T1-WI (same level as 2C) 45' after iv Gd shows the enhancing inflammatory tissue (arrowheads) in middle ear and attic surrounding the non-enhancing cholesteatoma under the tegmen (arrows).

Fig. 2E  Coronal SE EPI DWI shows the typical interface artefact between temporal lobe and temporal bone (arrowheads). The cholesteatoma cannot be seen due to the artefact.

Fig. 2F  Coronal and transverse single-shot TSE DWI clearly show the small very hyperintense lesion under the tegmen on the left side compatible with cholesteatoma. Note the complete lack of artefacts at the interface between temporal lobe and temporal bone. The lesion can be clearly visualized on both transverse and coronal images (arrows). Compare to figure 2E. In retrospect, the lesion can merely be suspected in the interface artefact of figure 2E on the left side.

Case Report 3

17-year-old boy with prior surgery for cholesteatoma with primary bony obliteration technique on both sides. In this technique the mastoidectomy cavity is filled with bone chips and bone paté in order to avoid recurrent cholesteatoma. Patient was presented for evaluation of the right side.

Fig. 3A  Transverse and coronal CT images show a complete homogeneous opacification of the right mastoidectomy cavity with bony material (arrows). The residual middle ear cavity remains well aerated (arrowheads). On CT, there is no suspicion for cholesteatoma in the obliterated cavity nor in the aerated residual middle ear cavity on the right side.

Fig. 3B  Coronal SE EPI DWI shows no clear hyperintense abnormalities on either right or left side.

Fig. 3C  Coronal single-shot TSE DWI shows no clear hyperintensity on the right side but, surprisingly, there is a clear nodular hyperintensity on the left side (arrow), suggestive of a small residual cholesteatoma. Compare to figure 3B. Note the homogeneous signal of the lesion and the complete absence of the interface artefact.

Fig. 3D  TSE T1-WI 45' after iv Gd shows a corresponding nodular non-enhancing lesion in the hypotympanon on the left side (arrows), compatible with a small residual cholesteatoma.

Fig. 3E  Transverse and coronal CT image through the left middle ear shows a complete and homogeneous opacification of the left mastoidectomy cavity with bony material (arrows). There is a clear nodular soft tissue lesion in the hypotympanum compatible with a cholesteatoma (arrowheads). Compare to figure 3C and 3D.

Discussion

High resolution CT scan still remains the primary examination tool for the evaluation of a patient suspected of having a middle ear cholesteatoma. It gives excellent information on the extension of the lesion, ossicular erosion and delineation of the tympanic segment of the facial nerve. It also clearly reveals erosion of the lateral semicircular canal and tegmen (1). In selected cases, MRI has an additional value for the evaluation of cholesteatoma extension and for the assessment of possible complications such as erosion of the lateral semicircular canal, invasion in the membranous labyrinth and invasion in the middle cranial fossa through an eroded tegmen (1). Several past reports have discussed the aspect of cholesteatoma on MRI. The aspect of a congenital temporal bone cholesteatoma or an acquired cholesteatoma on standard MRI sequences is well known. On T2-weighted images cholesteatoma has a slightly higher signal intensity than brain tissue (gray matter). On T1-weighted images, it has an isointense appearance with peripheral matrix enhancement. As cholesteatoma is avascular tissue, the center of the cholesteatoma never enhances contrary to inflammatory and/or granulation tissue (2, 3).
Recently, the aspect of cholesteatomatous tissue on echo planar diffusion-weighted MR images (SE EPI DWI) has been described. Congenital temporal bone cholesteatoma as well as acquired middle ear cholesteatoma exhibit a high signal on SE EPI DWI probably caused by a combination of restricted diffusion and a T2-shine through effect (4, 5, 6, 7). The major limitation seems to be the important air-bone interface artefact at the skull base, the distortion of the images and the low spatial resolution. Furthermore, smaller lesions (less than 5 mm) are still missed using the SE EPI DWI (8).
Moreover, in the past, several studies have shown the failure of MRI in demonstrating and delineating residual cholesteatoma before second-look surgery (9, 10). Therefore, second- look surgery, performed about one year after first-look surgery, remains the gold standard for detection of residual cholesteatoma up until now.
The combination of standard post-contrast MRI sequences combined with SE EPI DWI -up until now- seems to have the highest sensitivity for the detection of residual cholesteatoma. Again, a high number of residual cholesteatomas can be missed due to the often small size of these residual cholesteatoma pearls (2 to 4 mm) and the air-bone interface artefact noted at the skull base (8, 11, 12, 13, 14).
Recently, the use of late post-contrast T1-weighted images has been demonstrated to be of a great value in differentiating cholesteatoma from inflammatory and granulation tissue. It is stated that post-operative inflammatory and granulation tissue show a slow centripetal contrast uptake and can thus only be differentiated from (non-enhancing) cholesteatomatous tissue by using late post-contrast T1-WI images (15, 16).
By using single-shot TSE DWI we succeeded in overruling the above-mentioned major limitations of SE EPI DWI. Our first results show that prior size limitations to cholesteatoma detection seem to be overruled (Fig. 1). Furthermore, singleshot TSE DWI has no interface artefact at the temporal bone – temporal lobe border (Fig. 2). Further investigations and studies using the new combination of late post-contrast T1- WI and single-shot TSE DWI for the detection and delineation of small acquired middle ear cholesteatoma and pre-second look residual cholesteatoma have currently been started. We hope that the combination of late post-contrast T1-WI and single-shot TSE DWI has the highest sensitivity and specificity in order to replace second-look surgery for acquired middle ear cholesteatoma (Fig. 3).

*This information about this product is preliminary. The product is under development and not commercially available in the US and its future availability cannot be ensured.

References

[ 1 ] Lemmerling M, De Foer B. Imaging of cholesteatomatous and non-cholesteatomatous middle ear disease. In:
M. Lemmerling, S.S.Kollias. Radiology of the Petrous Bone, 1st edn. Springer Verlag Berlin Heidelberg New York pp 31–47.
[ 2 ] Martin N, Sterkers O, Nahum H. Chronic inflammatory disease of the middle ear cavities: Gd-DTPA-enhanced MR imaging. Radiology. 1990; 176: 399–405.
[ 3 ] Ishii K, Takahashi S, Kobayashi T, et al. MR imaging of middle ear cholesteatomas. J Comput Assit Tomogr. 1991;
15: 934–937.
[ 4 ] Robert Y, Carcasset S, Rocourt N, et al. Congenital cholesteatoma of the temporal bone: MR findings and comparison with CT. Am J Neuroradiol 1995; 16: 755–761.
[ 5 ] Fitzek C, Mewes T, Fitzek S, et al. Diffusion-weighted MRI of cholesteatomas of the petrous bone. J Magn Reson Imaging 2002; 15: 636–641.
[ 6 ] Maheshwari S, Mukherji SK. Diffusion-weighted imaging for differentiating recurrent cholesteatoma from granulation tissue after mastoidectomy: case report. Am J Neuroradiol 2002; 23: 847–849.
[ 7 ] Mark AS, Casselman JW. Anatomy and disease of the temporal bone. In: Atlas SW, Eds. Magnetic Resonance imaging of the brain and spine, 3rd edn. Philadelphia: Lippincott, Williams and Wilkins, 2001; 1363–1432.
[ 8 ] De Foer B, Casselman JW, Govaere F, et al. The role of MRI and diffusion- weighted images in the diagnosis of middle ear cholesteatoma. Acta Radiol Port 2002; 14: 89 (abstract).
[ 9 ] Kimitsuki T, Suda Y, Kawano H, et al. Correlation between MRI findings and second-look operation in cholesteatoma surgery. ORL J Otorhinolaryngol Relat Spec. 2001; 63: 291–3.
[ 10 ] Vanden Abeele D, Coen E, Parizel PM, et al. Can MRI replace a second look operation in cholesteatoma surgery? Acta Otolaryngol. 1999; 119: 555–61.
[ 11 ] Aikele P, Kittner T, Offergeld C, et al. Diffusion-weighted MR imaging of cholesteatoma in pediatric and adult patients who have undergone middle ear surgery. AJR Am J Roentgenol. 2003 ; 181: 261–5.
[ 12 ] Stasolla A, Magluilo G, Parrott D, et al. Detection of Postoperative Relapsing/Residual Cholesteatomas with diffusion-weighted echo-planar magnetic resonance imaging. Otol Neurotol 2004: 25; 879–884.
[ 13 ] J-Ph Vercruysse, B. De Foer et al. The value of Diffusion-Weighted MRimaging in the Diagnosis of Primary Acquired and Residual Cholesteatoma: a surgical verified study in 100 patients. Submitted for European Radiology.
[ 14 ] B. De Foer, J-Ph Vercruysse et al. The value of high resolution CT and MR imaging including diffusion-weighted images in the detection of postoperative residuel cholesteatoma. Submitted for European Radiology.
[ 15 ] Williams MT, Ayache D, Alberti C, et al. Detection of postoperative residual cholesteatoma with delayed contrast-enhanced MR imaging initial findings. Eur Radiol. 2003; 13: 169–74.
[ 16 ] Veillon F, Riehm S, Enachescu B, et al. Diffusion versus delayed post gadolinium FAT-SAT T1-weighted imaging of cholesteatoma of the petrous bone. Acta Radiol Port 2002; 14: 89 (abstract).