Korean J Radiol.  2001 Sep;2(3):151-158. 10.3348/kjr.2001.2.3.151.

MR Imaging-Histopathologic Correlation of Radiofrequency Thermal Ablation Lesion in a Rabbit Liver Model: Observation during Acute and Chronic Stages

• Lee JD
• Lee JM
• Kim SW
• Kim CS
• Mun WS

• KMID: 754100
• DOI: http://doi.org/10.3348/kjr.2001.2.3.151

Abstract

OBJECTIVE
To determine the ability of MR imaging to detect the pathological changes occurring in radiofrequency (RF) thermal lesions and to assess its accuracy in revealing the extent of tissue necrosis. MATERIALS AND METHODS: Using an RF electrode, thermal lesions were created in the livers of 18 rabbits. The procedure involved three phases. In the acute phase, six animals were killed the day after performing thermal ablation with RF energy, and two on day 3. In the subacute and chronic phases, eight rabbits underwent percutaneous hepatic RF ablation. After performing MR imaging, two animals were sacrificed at 1, 2, 4, and 7 weeks after the procedure, and MR-pathologic correlation was performed. RESULTS: In the acute phase, the thermal ablation lesions appeared at gross examination as well-circumscribed, necrotic areas, representing early change in the coagulative necrosis seen at microscopic examination. They were hypointense on T2-weighted images, and hyperintense on T1-weighted images. Gadolinium-enhanced MR imaging showed that a thin hyperemic rim surrounded the central coagulative necrosis. In the subacute phase, ablated lesions also showed extensive coagulative necrosis and marked inflammation at microscopic examination. Beyond two weeks, the lesions showed gradual resorption of the necrotic area, with a peripheral fibrovascular rim. The size of lesions measured by MR imaging correlated well with the findings at gross pathologic examination. CONCLUSION: MR imaging effectively demonstrates the histopathological tissue change occurring after thermal ablation, and accurately determines the extent of the target area.

Keyword

Liver, MR; Liver, interventional procedure Interventional procedures, experimental

MeSH Terms

Animal
*Catheter Ablation
Liver/*pathology/*surgery
*Magnetic Resonance Imaging
Male
Rabbits

Figure

• 

  Fig. 1 MRI and histopathologic findings immediately after RF thermal ablation. A. Gradient-echo T1-weighted image (TR/TE/FA, 153/5/90°) shows an ill-defined hyperintense lesion (open arrows) with a central hypointense spot (arrow). B. Turbo spin-echo T2-weighted image (TR/TE/NEX/ETL, 24000/99/4/11) demonstrates three zones, with a central hyperintense spot due to blood at the site of needle insertion (thin arrow), a hypointense thermally ablated lesion (open arrows), and a poorly demarcated hyperintense peripheral zone (thick arrows). C. Contrast-enhanced T1-weighted image (TR/TE/Nex, 153/5/2) depicts an RF thermal lesion as a hypointense perfusion defect area (arrowheads). There is a wedge-shaped perfusion abnormality adjacent to the ablated lesion (small arrows). D. Cut gross specimen demonstrates a central white cavity of tissue loss (arrowhead) and a wider zone of pale liver tissue (open arrows) surrounded by a small hemorrhagic rim (arrows), with normal liver peripherally. E. Microscopic examination reveals the area of the ablated lesion. Zone 2 indicates a wider zone of early necrosis (N), and zone 3, congestion and sinusoidal hemorrhage of the liver (H). Normal liver parenchyme (L) surround the lesion peripherally (hematoxylineosin stain; original magnification, ×20).

• 

  Fig. 2 Thermally ablated lesion in rabbit livers on day 7. A. T2-weighted image shows a central hypointense area with a peripheral hyperintense rim (arrows). B. Cut surface of the gross specimen demonstrates a discolored ablated area surrounded by a thin fibrotic layer (arrows). C. Microscopic examination reveals definitive change in the extent of coagulative necrosis (N) in the ablated lesions, with peripheral hemorrhagic congestion and mild fibrotic change at the periphery (arrows).

• 

  Fig. 3 MR and pathologic findings two weeks after RF ablation. A. Contrast-enhanced T1-weighted image depicts a well-demarcated hypointense lesion surrounded by a thick enhancing rim (arrows). B. Cut surface of the gross specimen shows a well demarcated, wedge-shaped, pale area with fibrotic capsule formation (arrows). C. Microscopic examination reveals central coagulative necrosis (N), with a thick rim of peripheral fibrotic capsule (F) infiltrated by chronic inflammatory cells (hematoxylin-eosin stain; original magnification ×20).

• 

  Fig. 4 Sequential changes in MR imaging findings in RF thermal lesions. A (Day 1), B (week 1), and C (week 4). T2-weighted images show that the extent of the area of low SI (arrows), corresponding to coagulative necrosis, increased during week 1 and thereafter gradually decreased.

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