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Definition

Formation of too much tissue necrosis resulting in undesired damage of underlying or surrounding tissue and resulting in functional impairment

Risk factors

 Cryosurgery without temperature control

 Tumors located over joints and tendons sheahs, or close to the coronary band [14, 15]

 Cryosurgery of ocular lesions [14, 15]

Pathogenesis

Necrosis and sloughing of the frozen tissue start from 7–10 days after cryosurgery and are commonly accompanied by a yellowish exudate and a malodourous smell which disappears once all necrotic tissue has been fully rejected (Figure 11.3). This is a normal evolution after cryosurgery. However, overly aggressive freezing results in necrosis of too much healthy tissue and may damage vital structures surrounding the tumor. This results in unwanted tissue necrosis and sloughing of neighboring tissue, which is one of the most serious complications after cryosurgery.

Prevention

Tumors for which cryosurgery is feasible should be carefully selected by determining the risk of damaging important surrounding or underlying structures. Thermocouple needles should be aplied into the tissues to be preserved around the lesion [13] and these tissues should not be cooled below 0 to –5°C. The risk of inadvertent freezing of vessels at the edge of the lesion is relatively low as the circulating blood is a source of heat, thus delaying the development of very low temperatures.

Figure 11.3 Sloughing of the cryonecrotic eschar 3 weeks after cryosurgery of a sarcoid at the inner aspect of the right thigh, with the normal accompanying mucopurulent discharge.

Source: Ann Martens.

The use of cryosurgery has been discouraged for periocular sarcoids as they are commonly located on or very close to the eyelids, resulting in a high risk of excessive scarring of the eyelids and/or damage to the globe [23]. However, cryosurgery for ocular squamous cell carcinoma’s can be performed safely if appropriate equipment and expertise are available [5]. Over‐freezing at that location is less likely to occur with N₂O (–89°C) compared to liquid nitrogen [8].

When using contact circulation probes for limbal squamous cell carcinomas, freezing occurs very fast and should be stopped when the frozen area exceeds 2–3 mm beyond the visible tumor margins. Detachment of the probe is then needed to stop further cooling down of the tissues. This can be achieved by applying 10–20 ml of saline solution at body temperature to the eye [5] ^. Once the probe is detached, the tumor is further allowed to thaw slowly.

Diagnosis

Diagnosis can commonly not be made within the first days after cryosurgery and the presence of oedema in the tissues to be preserved does not mean that they will become necrotic. It takes several days (at least 7–10) before demarcation of the necrotic tissue becomes evident and before a correct diagnosis of the extent of undesired tissue damage can be made.

Treatment

The necrotic tissue should be removed once it is demarcated (2–4 weeks after cryosurgery) to support second‐intention wound healing. In the case of joint or sheath penetration, standard wound care should be combined with repeated flushing of the synovial cavity and the standard management of a septic synovitis [24]. However, the prognosis is very guarded because of the loss of synovial capsule as a result of tissue necrosis. When globe perforation occurs as a result of cryosurgery, enucleation is the only treatment option.

Expected outcome

Necrosis of the joint capsule can result in a penetrating intra‐articular wound and subsequent joint sepsis which can be extremely difficult to manage and may lead to the destruction of the horse [14, 16]. However, even when the excessive slough of tissue does not result in joint penetration, extensive damage to the periarticular tissues, fibrous reactions and osseous peri‐articular new‐bone formation may occur, resulting in functional impairment and/or osteoarthritis (Figure 11.4). Similarly, necrosis of the tendon sheath wall can result in a penetrating intrasynovial wound and sheath sepsis.

Cryosurgery of periocular sarcoids can result in loss of the upper eyelid, unacceptable scarring of the eyelids, evisceration of the globe, and permanent loss of vision [14, 25].

Freezing of underlying nerves results in loss of nerve function, which can however be reversible. When peripheral nerves are frozen, the cellular components are destroyed but the fibrous part of the epineurium remains intact and will allow regeneration [13]. However, regeneration can also be incomplete [14].

Figure 11.4 (a) Excessive tissue necrosis occurring at the dorsal aspect of the pastern 8 days after cryosurgery for an equine sarcoid. The horse developed lymphangitis of the treated limbs in the first week after cryosurgery. On this picture, sloughing of a very large portion of the skin of the dorsal pastern has started. The wound eventually healed after a skin grafting procedure performed 40 days after the initial cryosurgery. Source: Ann Martens. (b) Lateromedial radiograph of the affected limb 7 months after cryosurgery. Although no penetration of the pastern joint occurred, tissue necrosis resulted in the development of extensive peri‐articular new‐bone formation and associated lameness.

Source: Ann Martens.

Freezing cortical bone causes cell destruction which reduces its strength. Spontaneous fractures have been reported months after cryosurgery [15]. The author has never experienced this complication, which might have been more common at the time cryotherapy was still indicated for the treatment of bony disorders such as fractured splint bones [2].

At locations with mainly underlying muscle, too extensive freezing mainly results in the sloughing of too large a portion of the surrounding skin, subcutaneous tissue and muscle, resulting in a large hole and a subsequent prolonged healing by second intention (Figure 11.5). Functional impairment is almost never an issue is these cases.