Cryoablation

Cryoablation is one of the local ablation techniques that have been used for several years. Low temperatures (from -20 to -30°C) cause direct freezing of tissue, denaturation of cell proteins, rupture of cell membranes, cell dehydration and ischaemic hypoxia that lead to the destruction of the neoplastic tissue. Cryoablation can be performed during laparotomy, or less frequently, during a laparoscopy. Ultrasound is utilised for real-time monitoring of the procedure. The technique consists in the insertion of a probe with a 5-10-mm diameter into the tumour; a cryogenic liquid (usually composed of liquid nitrogen at a temperature of -196°C) is then injected into the probe. Ultrasound is useful to monitor the extension of the frozen area. Usually 1 cm of healthy tissue is included in the frozen area in order to obtain complete treatment of tumour. For larger tumours multiple probes are utilised. Usually treatment consists in 1 or 2 cycles of freezing lasting 5-15 min, then the cryogenic probe is heated and pulled out of the site. The insertion site of the probe is compressed to achieve haemostasis.

Maximal extension of necrosis utilising 10-mm probes is about 7 cm. The size and shape of the necrotic area may be altered by anatomic factors such as the presence of vessels that due to the effect of the blood flow do not allow freezing. The efficacy of the treatment is assessed with imaging techniques (CT or MRI) and with a periodical dosage of tumour markers. Nowadays indications for cryotherapy are limited because this technique has been replaced by other ablation techniques.

The limitations of cryoablation are related to the need for a laparotomic or laparoscopic approach and the occurrence of major complications in about 10% of cases. Major complications after treatment are: post-operative bleeding due to vessel rupture after

Fig. 4a, b. RFA of liver metastases. a Before treatment the lesion is hypo-isoechoic. b After treatment the lesion becomes hyperechoic

Fig. 4a, b. RFA of liver metastases. a Before treatment the lesion is hypo-isoechoic. b After treatment the lesion becomes hyperechoic freezing, right pleural effusion, infection of necrotic area, biliary lesions with fistula and biliomas, thrombocytopenia, myoglobinuria with acute renal failure and DIC (cryoshock phenomenon). Mortality after the procedure is about 1-4%. Data on long-term response report local recurrences in 15% of patients and a 5-year survival for patients with hepatic metastases from colorectal cancer of 10-20%.

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