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Percutaneous MR Imaging– guided Radiofrequency Interstitial Thermal Ablation of Tongue Base in Porcine Models: Implications for Obstructive Sleep Apnea Syndrome¹

¹ From Depts of Radiology (S.G.N., J.S.L., C.H., F.K.W., I.C.M., C.B.A., M.M.H., J.L.D.), Otolaryngology (M.G., M.S.), Pathology (J.W.W.), and Biomedical Engineering (J.S.L., J.L.D.), Univ Hosp of Cleveland/Case Western Reserve Univ School of Med, 11100 Euclid Ave, Cleveland, OH 44106-5056 and Dept of Diagnostic Radiology, Cairo Univ Hosp, Egypt (S.G.N.). Supported in part by Siemens Medical Systems and Radionics and grants from Whitaker Foundation, American Cancer Society, and NIH RO1 CA-81431–01, R01-CA84433, R33 CA/AG 88144–01, and P20 CA91710–01. Received Aug 20, 2002; revision requested Oct 7; revision received Apr 23, 2003; accepted Jun 19. Address correspondence to J.S.L. (e-mail: lewin@uhrad.com).

View larger version (74K): [in a new window]   Figure 1.  A, Coronal diagram of the percutaneous approach for tongue base ablation shows the RF electrode (13) inserted percutaneously through the chin and advanced cranially in a strict midline trajectory to reach the tongue base without puncturing the tongue mucosa or risking any of the vital structures at the floor of the mouth. 1 = mucous membrane of tongue, 2 = tongue muscles, 3 = genioglossus muscle, 4 = geniohyoid muscle, 5 = hyoglossus muscle, 6 = sublingual gland, 7 = lingual vessels and nerve, 8 = mylohyoid muscle, 9 = body of mandible, 10 = submandibular gland, 11 = platysma muscle, 12 = skin. B, Coronal MR image from a series of images obtained with fast imaging with steady-state precision techniques (17.8/8.1; flip angle, 90°; number of signals acquired, three) with a temporal resolution of three frames per 22 seconds acquired during MR fluoroscopic guidance of the RF electrode into the base of the tongue. Note the lingual arteries (straight arrows) and surface mucosa (arrowheads). The RF electrode (curved arrow) can be stopped short of the mucosa, and the induced thermal lesion can be planned to lay entirely with the muscular portion of the tongue base.

View larger version (99K): [in a new window]   Figure 2.  A, Coronal and, B, sagittal spin-echo T1-weighted MR images (528/26; flip angle, 90°; number of signals acquired, four) confirm the position of the RF electrode prior to ablation. Note the smaller artifact associated with the RF electrode (curved arrows) on these spin-echo images compared with the gradient-echo image (Fig 1, B), although both were acquired with the phase-encoding direction perpendicular to the electrode shaft. Note also the delineation of surface mucosa (arrowheads) and lingual arteries (straight arrows).

View larger version (84K): [in a new window]   Figure 3.  Acute thermal lesion of the tongue base. A, Sagittal contrast-enhanced spin-echo T1-weighted (528/26; flip angle, 90°; number of signals acquired, four) MR image. B, Fast spin-echo T2-weighted (2,600/96; echo train length, seven; number of signals acquired, seven) MR image. C, Fast spin-echo STIR (2,700/48; echo train length, seven; number of signals acquired, seven) MR image. All images were acquired immediately after RF ablation with a low-field-strength (0.2-T) MR imager. Images show the typical MR appearance of acute thermal lesions of the tongue base, being hypo- or isointense at all pulse sequences and surrounded by hyperintense rims of reactive tissue changes on the T2-weighted and STIR images (arrowheads in B and C), with marginal enhancement on the postcontrast image (arrowheads in A). Note the RF electrode track (arrow in C). D, Corresponding gross pathologic specimen shows pale area of coagulation necrosis surrounded by well-defined dark hyperemic and hemorrhagic rim (arrowheads) and traversed by hemorrhagic puncture wound (arrow). E, Trichrome-stained histologic section of the same lesion shows basophilic staining of the muscle fibers at the site of acute thermal injury (arrowheads) and intact tongue mucosa. Examination of the corresponding hematoxylin-eosin-stained specimen (not shown) yielded less impressive cellular changes and barely defined thermal lesion boundaries. F, Magnified section of E demonstrates contraction banding of the myofibrils (arrowheads), which is a sign of acute muscle injury.

View larger version (70K): [in a new window]   Figure 4.  Chronic thermal lesion of the tongue base. A, Sagittal MR image obtained with high-resolution three-dimensional CISS (10.4/5.2; flip angle, 64°; number of signals acquired, two) and a high-field-strength (1.5-T) MR imager immediately after RF ablation in a chronic porcine model. Thermal lesion appears isointense to the adjacent intact tongue muscles and is surrounded by hyperintense reactive tissue changes (arrowheads). The RF electrode track is well defined as a hyperintense line (straight arrow). Note the MR-compatible fiducial coil (curved arrow) and the hyperintense line extending from the floor of the mouth to the site of the coil, indicating the track of the deployment needle. B, Maximum intensity projection image constructed from three-dimensional CISS data demonstrates topographic location of the thermal lesion (curved arrow) relative to the lingual arteries (straight arrow).

View larger version (17K): [in a new window]   Figure 5.  Chart illustrates mean (± SD) volumes of chronic thermal lesions measured immediately after RF ablation, at 2-week follow-up, and at 1-month follow-up on each of the contrast-enhanced T1-weighted images (CE-T1WI; black bars), T2-weighted images (T2WI; white bars), and STIR images (gray bars). Data show the continued shrinkage of thermal lesions during 1-month follow-up, and the volumes are significantly smaller with all pulse sequences at 1-month follow-up imaging than immediately after RF ablation. Note also the wide error bars in the 2-week and 1-month groups, indicating the variable rates of shrinkage among the individual thermal lesions.

View larger version (95K): [in a new window]   Figure 6.  MR appearance and histopathologic correlation of a chronic thermal lesion. Sagittal fast spin-echo STIR images (5,300/35; echo train length, seven; number of signals acquired, one) acquired with a high-field-strength (1.5-T) MR imager obtained A, immediately after RF ablation; B, at 2-week follow-up; and C, at 1-month follow-up. Note the rapid rate of thermal lesion shrinkage from 3.7 mL on the image obtained immediately after ablation (A) to 1 mL on the image obtained at 2-week follow-up (B) and ending as a thin band of enhanced scar tissue on the image obtained at 1-month follow-up (arrow in A-C). Corresponding gross pathologic specimen (D) and hematoxylin-eosin-stained (E) trichrome-stained and (F) histologic specimens demonstrate total replacement of the area of necrosis by a grayish dense fibrous tissue (arrowheads in D) that lacks inflammatory cells, denotes a healed scar (arrowheads in E), and stains blue with trichrome stain (arrowheads in F). Note the inward traction of the yet-intact surface mucosa by the contracting scar tissue (curved arrow in D-F). This effect illustrates the basic theory behind use of thermal energy to induce tongue base volume shrinkage as a treatment of OSA syndrome.

View larger version (89K): [in a new window]   Figure 7.  MR appearance and histopathologic correlation of a chronic thermal lesion that underwent a slower, yet still significant, rate of shrinkage than the lesion in Figure 6. Sagittal fast spin-echo STIR images (5,300/35; echo train length, seven; number of signals acquired, one) acquired with a high-field-strength (1.5-T) MR imager obtained A, immediately after RF ablation; B, at 2-week follow-up; and C, at 1-month follow-up. The thermal lesion had a volume of 2.8 mL immediately after RF ablation, 1.7 mL at 2-week follow-up, and 0.8 mL at 1-month follow-up (arrow). Corresponding gross pathologic specimen (D) and low- (E) and (F) high-power trichrome-stained histologic specimens obtained immediately after 1-month follow-up imaging. Rectangle on E indicates the magnified area that is F. These images demonstrate tissue changes associated with the early healing process, as represented by the circumferential encasement of the area of coagulation necrosis by fibrous tissue giving rise to four distinct layers of histopathologic findings as follows: 1, normal muscle tissue of the base of the tongue; 2, mature fibrous tissue; 3, active granulation tissue; and 4, coagulated (mummified) muscle tissue.