Heat Sink Effect on Tumor Ablation Characteristics as Observed in Monopolar Radiofrequency,Bipolar Radiofrequency,and Microwave,Using Ex Vivo Calf Liver Model

Thermal ablation of liver tumors near large blood vessels is affected by the cooling effect of blood flow, leading to incomplete ablation. Hence, we conducted a comparative investigation of heat sink effect in monopolar (MP) and bipolar (BP) radiofrequency ablation (RFA), and microwave (MW) ablation devices.With a perfused calf liver, the ablative performances (volume, mass, density, dimensions), with and without heat sink, were measured. Heat sink was present when the ablative tip of the probes were 8.0 mm close to a major hepatic vein and absent when >30 mm away. Temperatures (T1 and T2) on either side of the hepatic vein near the tip of the probes, heating probe temperature (T3), outlet perfusate temperature (T4), and ablation time were monitored.With or without heat sink, BP radiofrequency ablated a larger volume and mass, compared with MP RFA or MW ablation, with latter device producing the highest density of tissue ablated. MW ablation produced an ellipsoidal shape while radiofrequency devices produced spheres.Percentage heat sink effect in Bipolar radiofrequency : Mono-polar radiofrequency : Microwave was (Volume) 33:41:22; (mass) 23:56:34; (density) 9.0:26:18; and (relative elipscity) 5.8:12.9:1.3, indicating that BP and MW devices were less affected.Percentage heat sink effect on time (minutes) to reach maximum temperature (W) = 13.28:9.2:29.8; time at maximum temperature (X) is 87:66:16.66; temperature difference (Y) between the thermal probes (T3) and the temperature (T1 + T2)/2 on either side of the hepatic vessel was 100:87:20; and temperature difference between the (T1 + T2)/2 and temperature of outlet circulating solution (T4), Z was 20.33:30.23:37.5.MW and BP radiofrequencies were less affected by heat sink while MP RFA was the most affected. With a single ablation, BP radiofrequency ablated a larger volume and mass regardless of heat sink.     

An unusual parasagittal tumour with acute blindness and response to cerebrospinal fluid shunting.

We report a seven-year-old girl who presented with a sudden tumor apoplexy due to a parasagittal hemangiopericytoma. Following tumor excision, the child was noted to have bilateral optic nerve dysfunction and progressive papilledema, despite rapid overall neurological improvement. Based on the clinical features, we feel that this case represents an unusual form of visual deterioration related to impaired CSF absorption somehow precipitated by the acute tumour apoplexy. This unusual case of blindness responded significantly to CSF shunting. Several reports exist describing raised intracranial pressure with papilledema caused by nonthrombotic sinus occlusion due to tumors in proximity to the posterior superior sagittal sinus, torcular herophili and the jugular outlet. Communicating hydrocephalus, pseudotumor syndrome or intracranial venous sinus obstruction should be considered when otherwise inexplicable visual loss coexists with optic nerve dysfunction and papilledema. We emphasize the importance of a thorough search for the cause of visual loss.