The value of cryoablation in orbital surgery

In orbital tumors treatment is typically indicated in growing lesions or if they become symptomatic [1, 2]. Such typical symptoms include orbital protrusion, double vision, and visual decline [1, 2]. In most of these cases, complete surgical removal is the treatment of choice. If possible, entire removal of the orbital mass or tumor should be performed without penetration of the lesion [1, 2]. A variety of different surgical corridors are nowadays available including traditional open microsurgical transcranial and transorbital but also endoscopic transcranial, transorbital, and transnasal approaches depending on the different locations of tumors within the orbit [1‐8].

Independent of the chosen surgical approach, meticulous preparation and dissection of the orbital mass or tumor without harming surrounding healthy structures such as the globe, ocular muscles or nerves needs to be performed. Eventually, after the lesion is freed from all adhesions, one piece removal should be performed. Different techniques and instruments such as grasping forceps or placement of a suture through the mass can be used; however, the frailty of some of these masses or their capsule puts them at risk of rupture and opening during this maneuver which might complicate lesion removal due to the narrow and complex retro-orbital conditions.

Another option to gently grasp a lesion without perforating it may be to use a cryoprobe [1, 7, 9]. In general, cryosurgery is used in various disciplines for different diseases. These include dermatological surgery, oral and maxillofacial surgery but also general and gynecological surgical applications for tumors and other conditions [10‐14]. In most of these treatments the aim is maximum cellular destruction by rapid freezing [15].

Already in 1975 the use of the adhesive effect of a cryoprobe for grasping and gentle removal of orbital lesions was described by Putterman and Goldberg in a small series of 4 patients [9]. Following this, various probes have been developed and used to facilitate orbital tumor removal. Aim of this report is to give an overview of the technical background and different uses together with a discussion of the most appropriate conditions to apply such a cryoprobe in orbital surgery.

The method of destroying tissue by freezing is called cryoablation. Cryoablation was first introduced by the English physician James Arnott (1797–1883) who used a combination of salt and crushed ice to treat breast, uterine and skin cancer [10, 12]. Since then, it has found many suitable areas of application as it is simple, cheap and safe to use in medicine. Resulting from the testing of various different cooling agents, liquid nitrogen has emerged as the most popular cryogen for medical use with achievable low temperatures of −197 °C but other possible agents used today include noble gases like argon but also oxygen, nitrous oxide or carbon dioxide [14, 16, 17].

In general, the lesion must be targeted with the cryo-probe. Once in physical contact, the probe is rapidly cooled down and removes heat from the lesion by conduction. The cryoprobe contains the pressurized gas which flows out through a narrow opening. During this process the gas rapidly expands at room temperature and exhibits the Joule-Thompson cooling effect [16]. This effect leads to rapid cooling of the metallic probe itself which then transfers the freezing effect to the surrounding tissue [16].

The extent of cellular injury may be influenced by the cooling rate, the target temperature, cooling duration and the thawing rate [17]; however, in nearly all tissues cell death is induced by cooling rapidly below −40 °C [15]. Cell death may occur due to direct injury to cells and indirect mechanisms that induce changes to the cellular microenvironment. Such direct damage occurs through ice crystal formation in the extracellular space during the freezing process [16, 17]. Due to the increased osmolality, more intracellular water is withdrawn, which leads to dehydration of the cells. If cooling occurs rapidly, intracellular ice formation leads to physical cellular damage and cell death [16]. Contrary to the freezing process thawing usually occurs in the extracellular space first and leads to water influx into the cells. This eventually can lead to swelling and bursting which also creates direct injury to the cells [16, 17]. In contrast to the freezing process, more damage occurs if thawing happens slowly [17]. Following this, indirect cell damage occurs via apoptosis processes and inflammatory changes in the surrounding damaged tissue and its microenvironment [16].

In addition to these ablative effects, cryoprobes also have an adhesive effect that became of interest as a tool in modern surgery especially for the use during minimally invasive procedures.

The abovementioned ablative processes of cryotherapy have been used in various surgical disciplines. These included dermatological, oral and maxillofacial, general and gynecological surgery [10‐12]. Especially in recent years, the field of cryosurgery received a new wave of interest in the treatment of prostate cancer and breast cancer [13, 14].

Although cryosurgery has been in medical use for a very long time, it has not yet had a major role in general neurosurgery; However, cryosurgery shows its strength especially when it comes to interventions in the narrow and complex orbital anatomy when removing well-circumscribed lesions. The cryoadhesive effect makes the removal of these lesions gentle and safe. As there are now single-use cryoprobes that do not require a large gas tank, cryosurgical devices should be considered part of every orbital surgeon’s standard armamentarium.