 |
Slide 1 |
Gun Shot Wounds of the Eye and Orbit
Mark R. Levine, MD · Amarpreet Singh, MD · Toni Meyers, MD
In 1977, gunshots caused 31,636 fatal injuries and 100,000 nonfatal injuries in the United States. The lifetime costs of treating all US gunshot wounds (GSW) in 1994 were $2.3 billion. The average medical cost of a gunshot injury was approximately $17,000, 49% of which was covered by taxpayers, 18% by private insurance, and 33% by other sources.1 Not only are gunshot-related injuries prevalent and associated with a significant cost; they create a financial burden that affects much of society.
Patient 1
A 20-year-old man, wounded by a shotgun blast fired from a distance of 10 feet, sustained multiple facial injuries and several double perforations of both globes (Slide 1, Slide 2). Visual acuity revealed light perception in both eyes. Slit lamp examination showed bilateral hyphemas, irregularly dilated pupils, and vitreous hemorrhages. Plain films of the face and orbit showed multiple intraorbital and intracranial shotgun pellets (Slide 3). The facial wounds were debrided and explored. The corneoscleral perforations were closed; however, no attempt was made to close them given the number of posterior perforations and their technically challenging locations. When last examined, the patient had light perception vision in both eyes.
|
|
|
This case illustrates the devastating injuries that can result from a shotgun (firing velocity 1,354 feet per second [fps]).
Patient 2
A 32-year-old woman was shot with a .38 special high-velocity revolver. The bullet penetrated the left zygoma, traversed the left retrobulbar space, and lodged intracranially. On arrival at the hospital, the patient was comatose and had a markedly proptotic globe and a 4+ afferent pupillary defect (Slide 4). Plain films of the orbit showed a large bullet fragment intracranially (Slide 5). A computed tomography (CT) scan showed marked disruption of the retrobulbar space as well as of the bony orbital walls (Slide 6). Metallic foreign bodies were also apparent. The CT scan with contrast of the brain showed many areas of infarction (Slide 7). The patient died 3 days after hospital admission.
|
|
This case demonstrates the amount of kinetic energy released from a high-powered hand gun (firing velocity 1,020 fps).
An interdisciplinary approach is required for managing orbit gunshot wounds. The most fundamental rule when caring for a trauma patient is the ABCs (airway, breathing, and circulation). The airway and cardiopulmonary status is the primary consideration in the initial management of a patient with an orbit gunshot wound. Hemorrhages and shock should be controlled and a complete neurological examination obtained (to rule out intracranial and spinal cord injuries) prior to the ophthalmologic evaluation. Every effort should be made to obtain an accurate history. The type and mechanism of injury, previous medical problems, tetanus status, allergies, and current medications are all necessary information and may affect the management of an injured patient.
|
|
Plain films, orbital ultrasound, CT scan, and magnetic resonance imaging (MRI) are useful for detecting and clarifying lesions. Orbital ultrasound aids in detecting posterior ocular lesions in the setting of vitreous hemorrhage, hyphema, or other instances where visualization of the posterior segment is difficult or impossible, though it has poor penetration of the orbital apex. Axial and coronal CT scanning are crucial in the evaluation of gunshot trauma as they provide visualization of soft tissues, bone structures, and foreign bodies. Axial and coronal CT scanning can also demonstrate unsuspected intracranial and paranasal sinus injuries. Contrast-enhanced CT images as well as magnetic resonance angiography and venography are valuable in cases of suspected vascular injury (i.e., carotid-cavernous sinus fistula or dural arteriovenous malformations).2 High-resolution, radionuclide cisternography and CT cisternography are also available to detect sites of cerebrospinal fluid (CSF) leak. Plain films are useful for detecting bony defects and radio-opaque foreign bodies, but plain films have been largely replaced by the widespread availability and ease of CT scanning.
MRI is not as useful as a CT scan in the initial stages because it does not show bony abnormalities. One must remember that MRI is contraindicated in patients who have a ferric implant or if the foreign bodies are suspected to be ferro-magnetic. In addition, the longer scanning time and motion artifact in an acutely traumatized patient may make this imaging modality less practical. However, MRI provides better resolution than CT scans for low-density objects such as wood and vegetable matter. MRI is also superior in demonstrating injuries involving the optic canal and the optic nerve at the nerve's intracanalicular portion.3
Gunshot wounds cause tissue disruption through the crushing effect of the bullet as it traverses the tissue and through the stretching reaction of tissue by temporary cavitations (i.e., the formation of a momentary cavity a few milliseconds following the tract of the missile). The most important factor in determining the force of injury from a gunshot wound is the velocity of the missile (Table): the higher the velocity, the greater the rate of dissipation of kinetic energy at impact, and the greater the damage. One of the three laws of thermodynamics is that energy cannot be created or destroyed. It follows that on impact, a high-velocity missile dissipates its kinetic energy into other forms (e.g., heat, vibration, mechanical and vacuum forces), all of which can damage tissue. At high velocities, the bullet will likely fragment, causing even more tissue destruction.
|
|||||
| 12 gauge shotgun | 1354 | ||||
| 22 | 1060 | ||||
| .38 special | 845 | ||||
| .38 special high velocity | 1135 | ||||
| 357 magnum | 1298 | ||||
| Colt 45 | 850 | ||||
| M-16 | 3250 | ||||
In 1985, Fackler and Malinowski4 reported four components of missile-tissue interaction: penetration, missile fragmentation, permanent cavity, and temporary cavity. The first three components are a result of the wounding mechanism, which depends on the kinetic energy of the missile. The fourth component (temporary cavitations) is related to a stretch mechanism. Its disruptive effect depends on the intrinsic elasticity of the tissue; more destruction is likely to occur in nonelastic tissue (e.g., liver) than in elastic tissue (e.g., striated muscle).5 Temporary cavitations are greatest with high-velocity bullets that yaw or tumble as their path in flight becomes unstable.
Low-velocity and high-velocity gunshot wounds have different wound characteristics. A low-velocity gunshot wound exhibits entrance and exit wounds with a small track of tissue damage. In contrast, high-velocity gunshot wounds exhibit small entrance and large exit wounds (Slide 8, Slide 9).
|
|
The spectrum of ocular injuries caused by gunshot wounds is enormous,6,7 ranging from a small contusion to an ocular perforation with intracranial involvement. Generally, injuries may be classified as contusive injuries or penetrating/perforating injuries.
Contusive injuries result from the cavitation effect and from the shock waves generated by high-velocity bullets. Contusive injuries include hemorrhage (hyphemas or choroidal, vitreous, retinal and retrobulbar hemorrhages), angle recession, iridocyclodialysis, concussive cataract, lens dislocation, retinitis sclopteria, retinal edema, retinal detachment, and nerve avulsion.
Penetrating/perforating injuries occur anywhere in the globe and should be designated by location and extent (e.g., penetration, perforation, double perforation). Late effects from severe orbital cranial trauma secondary to gunshot wounds consist of orbital hematoma, orbital cellulitis and abscess, meningitis, brain abscess, meningoencephalocele, carotid-cavernous fistula, CSF rhinorrhea, tetanus, proptosis, enophthalmos, diplopia, and blindness.8,9
The location and extent of injury directly correlate with visual prognosis. The more posterior the injury, the worse is the prognosis for visual rehabilitation.10,11 Additionally, penetrating injuries are associated with lower visual potential than nonpenetrating injuries.
Management of patients with orbit gunshot wounds depends on the location of the projectile. Ancillary radiographic studies such as plain films and CT scans are critical first steps in locating and pinpointing the foreign body. Surgery should be considered in cases when the projectile is readily accessible. An inaccessible projectile located in the posterior portion of the orbit can often be left in place. However, surgical removal should be considered in the setting of marked orbital inflammation, infection, or CT evidence of optic nerve impingement with associated optic neuropathy.
Operative management depends on the type of injury and its mechanism. Low-velocity gunshot wounds generally cause mild soft tissue injuries and therefore immediate primary closure usually gives satisfactory results. In contrast, high-velocity gunshot wounds cause not only severe soft tissue loss but also bone loss requiring more complex intervention. Uncomplicated double perforations of the globe may be treated as soon as the patient is neurologically stable.
Primary closure of all perforation sites is desirable in all patients, despite the difficulty of closing posterior perforations. If a patient is neurologically unstable, then delayed primary closure may be anticipated. The additional time may help the surgeon, patient, and patient's family decide whether to surgically repair the perforations or proceed with removal of the eye. Evisceration is preferred over enucleation if the globe is lacerated beyond repair. Evisceration is technically easier and yields better cosmetic and functional results because it leaves the orbital anatomy relatively undisturbed. The common complications of enucleation (e.g., hypo-ophthalmos, superior sulcus deformity, and motility disturbances) are minimized in evisceration. Sympathetic ophthalmia, the major concern of evisceration, has been rare in our experience.
The treatment of eyelid, periorbital, and facial injuries depends on whether the wounds are infected. Noninfected wounds with little contamination are irrigated copiously and explored with fine curettes for foreign bodies that should be removed whenever possible. Hemostasis should be well maintained with only minimal debridement. Infected wounds with contamination should also be irrigated copiously, explored for foreign bodies, debrided, and treated with intravenous antibiotics. Severely contaminated areas may be packed open with antibiotic-impregnated gauze and then closed as a delayed primary closure 3 or 4 days later. The results of delayed primary closure are as cosmetically acceptable as those obtained with immediate closure.
The eyelids are meticulously repaired following plastic closure techniques utilizing 6-0 and 7-0 silk for the lid margin, 6-0 and 7-0 vicryl for the tarsal plate, and 6-0 nylon for the skin. The lacerated canicular system is intubated with silicone tubes (e.g., Monoka or Crawford tubes) and the canicular laceration closed end-to-end with 9-0 or 10-0 nylon. Associated orbital fractures with bony displacement are treated by placing the bony fragments as close as possible. For a severe bone loss or extensive communition, grafts of autogenous bone or insertion of alloplastic materials is indicated. Alloplastic material should be avoided in infected areas, as fistulas will form and extrusions can occur. Moreover, in this environment, autogenous bone grafts will absorb. Therefore, it may be best to wait until a later date to reconstruct the orbit. Better reconstruction may be anticipated with 3-dimensional CT scans, which can produce copy templates of missing bony structures.
