Tomoyuki Kashima was graduated Medical school of Gunma University in 2002 and trained general ophthalmology in Department of Ophthalmology in Gunma University. He achieved oculoplastic fellowship program in Seirei Hamamatsu Hospital, Shizuoka, Japan from 2005 to 2007. He became the chief of oculoplastic and orbit surgery in Gunma University from 2007, and also become council member of Asia Pacific Society of Ophthalmic Plastic and Reconstructive Surgery from 2010 to 2014. He achieved International fellowship program in UCLA Stein Eye Institute from 2015 to 2016.
Pathology of Fractures
Before treatment, clinicians must assess when and how the trauma occurred within the periorbital region. There are two possible mechanisms explaining orbital fractures, the hydraulic and the buckling theory . When the intraorbital pressure rises suddenly, the indented force causes a deformity in the orbital floor and wall, which leads to bone fracture. A fracture could also be caused by direct dislocation of the globe to the walls . As discussed in the previous chapter, age-related changes in bone hardness contribute to the dislocation of the fractured bone and orbital contents, which leads to subjective symptoms.
Orbital fracture results in dislocation of bones and herniation of orbital contents. Due to these conditions, several symptoms could contribute to impaired quality of life for the patient. A dislocated bone may lead to the enlargement of the orbital cavity, and the globe could exhibit enophthalmos. Both the herniated orbital muscle and fat at the fracture site may cause impairment of ocular movements, because there are specific connections between orbital muscle and orbital fat . A sharp edge fat of the bone could significantly impair EOM, and the patient could experience pain during eye movement. Another symptom of orbital fracture is nausea and vomiting from the oculocardiac reflex (Aschner phenomenon) . The orbital tissues have sensory nerves which originate from the vagus nerve, a motor and sensory nerve of internal organs, which mainly controls the circulatory system, cardiovascular system, and gastrointestinal system. When the orbital tissues are herniated and tightly entrapped, they become congested and damaged, resulting in further damage to the orbital branch of the vagus nerves, causing nausea or vomiting via the oculocardiac reflex.
Trapdoor fracture is the most common type of fracture in young patients, especially in those under 20 years of age . As discussed in the previous chapter, because the bone is soft in young patients, clinical features and subjective symptoms differ from adults. When blunt trauma occurs, the adult orbital bone breaks. However, the young orbital bone is too soft to break and completely dislocates into the sinus, so that only a part of the orbital wall breaks. After an orbital bone break, the elevated intraorbital pressure causes orbital tissue, such as muscle or orbital fat, to herniate into the adjacent sinus. Some orbital bones may not break completely and are thus able to return to their original position, causing entrapment of herniated orbital muscle and fat. In trapdoor fractures, retention of entrapped extraocular muscle may occur and cause irreversible damage due to congestion and lack of blood from venous occlusion, if surgical procedures to release the tissues are not performed within 24 h . In these cases, the extraocular muscles not identified intraorbitally are referred to as “missing rectus” (Fig. 14.1) . The density of extraocular muscle is the same as a hemorrhage in the sinus, thus, in those cases identification of herniated muscles are difficult. However, cases with only orbital fat entrapment present a different condition. Orbital fat exists both as a filler of the orbit and a lubricant for eye movement. Prolapsed orbital fat impairs extraocular motility, thus the release of prolapsed orbital fat should be considered in orbital fracture. However, surgical indications are not as emergent as with muscle herniation, but the surgery should be performed within several days.
A case of “missing rectus” in the right orbit. The inferior rectus appears absent from the right orbit, but is actually dislocated into the maxillary sinus. Diagnosis using CT scans is misleading in this situation, because the density of the muscle is the same as the hemorrhage
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In the adult patient, open-type fracture is the most frequent and is a well-known result of periorbital blunt injury. In this type of fracture, the bones are dislocated and orbital tissues do not become entrapped. The patients’ symptoms are therefore mild EOM impairment and enophthalmos . To diagnose open-type fractures, coronal computed tomography (CT) scanning may be suitable. Coronal section CT scans can show both sides of the orbit, in the same section, to compare both orbital shapes (Figs. 14.2, 14.3, 14.4, 14.5, 14.6, and 14.7). During diagnosis, the clinician should see a soft tissue image, not a bone image. In cases with orbital fracture, the locations of the bones have less importance than understanding the degree of herniation of orbital contents. In a bone image, only the dislocation of bones and not the severity of the dislocation of orbital contents may be observable. However, in soft tissue images, bones, rectus muscles, and orbital fat can be observed in the same scanned section, which is useful in diagnosing the severity of the orbital fracture. In these CT scans, the location of the fractured bones should be identified to determine if they can be reused to reconstruct an orbital wall defect. The surgeon must also identify which hinge of the fracture to approach during the dissection of the fracture in the periorbital region.
The trapdoor fracture on the orbital floor of the right eye. The inferior rectus and surrounding orbital fat herniated and caught in the sight, which leads to impairment of supraduction of the right eye
Right orbital fracture with lateral hinge in a coronal section. A common site of orbital floor fracture is the infraorbital canal, which is the thinnest area, due to the presence of the infraorbital nerve (arrowheads)