Radiofrequency ablated lesion in the normal porcine lung: long-term follow-up with MRI and pathology.
OBJECTIVE
To evaluate the effectiveness of magnetic resonance imaging (MRI) in reflecting histopathologic changes after radiofrequency ablation (RFA) to the lung and to assess accurately the extent of tissue necrosis for evaluating untreated lesions.


METHODS
Percutaneous RFA was performed on 72 lung regions in 12 pigs under computed tomographic guidance. After performing MRI, the animals were divided into three experimental phases: in the acute phase, 4 pigs were killed immediately after the procedure; in the subacute phase, 4 pigs were killed at 1 week; and in the chronic phases, 2 pigs were killed at 4 and 8 weeks after the procedure, respectively. MRI-histopathologic correlation was performed.


RESULTS
In the acute phase, the inner zone showed hypointensity on T2-weighted images and isointensity on T1-weighted images, with a lack of enhancement on contrast-enhanced T1-weighted images, representing early changes in coagulative necrosis on histopathologic examination. The outer zone showed hyperintensity on T2-weighted images and isointensity on T1-weighted images, with ring-like enhancement on contrast-enhanced T1-weighted images. The histopathologic section showed alveolar fluid collections and congestion. In the subacute phase the MR zone pattern was essentially similar to that of the acute phase, but the ablated lesion showed extensive coagulative necrosis with a fibrovascular rim on histopathologic examination. In the chronic phase, there was no change in the zone pattern on MRI. The lesions showed gradual resorption of coagulative necrosis. The area of coagulative necrosis correlated closely with the histopathologic size (p < 0.05).


CONCLUSIONS
MRI effectively visualized the histopathologic changes after RFA and accurately determined the extent of the necrotic lesion. MRI is potentially a useful modality for evaluating therapeutic efficacy after RFA to the lung.
Oyama
Yoshimasa
Y
Department of Radiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka 545-8585, Japan. yoshimasa519@yahoo.co.jp
Nakamura
Kenji
K
Matsuoka
Toshiyuki
T
Toyoshima
Masami
M
Yamamoto
Akira
A
Okuma
Tomohisa
T
Ikura
Yoshihiro
Y
Ueda
Makiko
M
Inoue
Yuichi
Y
D000818:Animals; D017115:Catheter Ablation / Q000379:methods*; D003287:Contrast Media; D005122:Exudates and Transudates; D005355:Fibrosis; D006097:Granulation Tissue / Q000473:pathology; D007089:Image Enhancement; D007249:Inflammation; D008168:Lung / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D023421:Models, Animal; D009336:Necrosis; D018919:Neovascularization, Physiologic; D011650:Pulmonary Alveoli / Q000473:pathology; D011654:Pulmonary Edema / Q000473:pathology; D015641:Radiography, Interventional; D013552:Swine; D013997:Time Factors; D014057:Tomography, X-Ray Computed
D003287:Contrast Media