MR-guided cryotherapy of a breast cancer metastasis to the liver

Imaging Findings

A 38 year old women was referred to our department for percutaneous ablation of two intrahepatic lesions. One year ago, she underwent mastectomy, chemotherapy and irradiation of the chest wall due to right-sided breast cancer. Recent MR imaging (multiplanar T2-weighted turbo spin echo sequence, 1.5 T Gyroscan ACS NT, body coil) revealed two intrahepatic metastases with diameters of 2.5 cm (center of the right lobe) and 3 cm (segment 4a, Fig. 1a). Additionally, a splenic lesion, also suspicious for metastasis (Fig. 5b), was seen. Considering the fact that the splenohepatic metastases remained unchanged despite completed chemotherapy and therefore are insensitive to further chemotherapy protocols, a palliative treatment was chosen and resective liver surgery was refused. As hyperthermal ablation techniques like laser or radiofrequency ablation are usually painfull and require a thorough analgosedation or general anesthesia, the patient choose (after offering both, hyper- and hypothermal ablation techniques) to receive a percutaneous cryoablation. The intervention was performed under MR control. The entry point for biopsy on the skin was determined by imaging a gadolinium-filled grid (aqueous solution 1:200) using a T1-weighted dynamic gradient echo sequence with prepulse. 2 MR-compatible cryotherapy probes (Fig. 2a) with 3.4 mm in diameter and a length of 12 cm (Galil Medical, Yokneam, Israel) were placed within the right central lesion under local anesthesia through a 10 F angiographic introducer sheath (Terumo, Japan). The probes are tapered and were inserted using the trocar-technique after sharp incision of the skin. This procedure as well as the monitoring of the freezing process was imaged by an interactive ultrafast T2-weighted single-shot turbo spin echo sequence using the zoom imaging method (LoLo, Fig. 3a, b). When the frozen tissue exceeded the tumor margin by more than one centimeter, the freezing was stopped and the ice was allowed to thaw passively. The freezing was repeated two times. The maximum diameter of the ice formation was 4 cm perpendicular to the probe shaft and 4.5 cm along the shaft axis. Neither during the freezing nor after the intervention the patient complained about pain. After the ablation, the probes were removed and the puncture channels were sealed injecting a two-component tissue glue (Tissucol Duo S®, Baxter, Germany). This intervention was performed for treatment of the second metastasis in segment 4a one week before. Immediately after both interventions, the lesions and the surrounding tissue appeared edematous on fat suppressed T2-weighted GRASE sequences (Fig. 4a, b). On contrast-enhanced spiral CT images (Fig. 5a, b) one week after the last intervention, the previsously frozen areas including the metastases showed no enhancement after contrast agent injection and thus were assumed to be necrotic.

Discussion

Cryotherapy or cryosurgery is the irreversible damage of tissue by use of low (subzero) temperatures. In brief, the damaging process of an undesired tissue occurs by heat transfer or due to direct or indirect contact with a coolant. As the heat is removed from the tissue, a frozen region begins to form and grows outward from the coolant. When the undesired tissue is frozen, the freezing process is stopped and the tissue is allowed to thaw. The damaged tissue sloughs and scarring occurs soon afterwards. As the previously frozen tissue is left in situ, cryotherapy is an interstitial and non-resective ablation technique. Cryotherapy is an old and well known technique, which had a renaissance during the last decades when ultrasound was available for on-line monitoring of the ice extension. Until recently, when the diameter of the cryoprobes was available in sizes over 5 mm only, it was used intraoperatively only. Liquid nitrogen (LN2, -195.6°C) has been the only feasible coolant for a long time, but other coolants like nitrous oxide or argon gas were discovered to be as effective as LN2. Based on the Joule-Thomson effect which explains a rapid temperature drop, if a high pressurized gas expands suddenly, modern gas expansion systems allow cooling capacities between –150°C and –180°C, depending on the probe design and diameter. The most important advantage over LN2-based systems is the fact, that the deep temperatures "arise" at the probe tip and, opposite to LN2-based systems, the supplying tubes remain at room-temperature. Therefore, the probe shaft needs no thermal insulation. Consequently, smaller diameters of the probes can be manufactured and a percutaneous application is possible. Another advantage of modern gas expansion systems is a faster cooling rate, which is defined astemperature drop per minute making "pre-cooling" of the supplying tubes unnecessary. The most important advantage of the combination of cryoablation and interventional MR imaging is the precise delineation of frozen tissue and the multiplanar imaging capabilities of MR imaging. Due to an extreme shortening of T2- and T1-relaxation times, nearly no signal of frozen tissue can be obtained by conventional MR pulse sequences. In consequence, frozen tissue is imaged signal free yielding a high contrast to unfrozen soft tissue. The use of modern ultrafast pulse sequences like the LoLo sequence (acquisition time: 800 ms/image) increases the patient comfort and the safety during the intervention, because no breath-holding is neccessary during imaging. Thus, an optimal information about the actual extension and size of the ice formation is available at any time during the intervention. Another characteristic of cryotherapy is the fact, that deep temperatures are intrinsically analgesic. Except for percutaneous insertion of the probe which is performed under local anesthesia, no additional analgesic drugs are required. This makes cryotherapy suitable for tissue ablation in tender regions like in subcapsular or paraportal location. Another potential of cryotherapy is the possibility to ablate target tissues even in the proximity to large blood vessels. Because of the heat transfer of blood flow in arteries and veins, a severe damage of the vessel wall is unlikely due to the temperature balance between the ice on the one and the warm blood flow of the other side of the vessel wall. In conclusion, the combination of percutaneous cryotherapy and interventional MR imaging enables a precise and safe focal tissue ablation with a high temporal and spatial resolution of monitoring the ablation process. Due to its specific characteristics, cryotherapy is ideally suited for percutaneous treatment of liver lesions in anatomically critical regions. In opposition to hyperthermal ablation techniques, the imaging of frozen tissue does not require dedicated temperature sensitive sequences and can be performed on all interventional MR systems.

Differential Diagnosis List

Final Diagnosis

Successful palliation of hepatic metastases using MR-guided percutaneous cryotherapy

URL:	https://www.eurorad.org/case/1115
DOI:	10.1594/EURORAD/CASE.1115
ISSN:	1563-4086