Computed tomography findings of orbital floor trapdoor fractures in children

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rbital floor blowout fractures resulting from blunt trauma exhibit unique features in the pediatric population compared with adults.1,2 In children, more flexible bones and resilient periosteum lead to narrower bone separation and transient displacement of a bone flap that subsequently snaps back into its original position, termed a trapdoor fracture.3,4 This can result in entrapment of the adjacent extraocular soft tissue and muscle.The infraorbital rim remains intact.However, in adults, brittle orbital bones and fragile periosteum lead to a wider fracture area (open-door or comminuted-type fractures).1,2 The fracture line and herniated soft tissue are more extensive, and symptoms are primarily related to enophthalmos.5 PURPOSE Orbital floor trapdoor fracture is a special type of blowout fracture seen primarily in children, and it can cause entrapment of intraorbital tissue and the inferior rectus (IR) muscle.It may be overlooked because the radiologic findings can be subtle.This study reviews the clinical and computed tomography (CT) findings in children with orbital floor trapdoor fractures. METHODSWe retrospectively analyzed the clinical and CT findings of children with orbital floor trapdoor fractures over a 20-year period. RESULTSA total of 43 patients (35 boys, 8 girls; age range, 2-17 years; mean age, 11.5 years) were included in the study.Nineteen patients had intraorbital tissue herniation through the fracture into the maxillary sinus with abnormal alignment and traction of the IR muscle toward the fracture site, termed a tethered muscle (group 1).Thirteen patients had only intraorbital tissue herniation with the IR muscle in a normal position (group 2).Eleven patients demonstrated herniation and entrapment of both the intraorbital tissue and the IR muscle (group 3).Ocular motility restriction occurred in 74% of patients in group 1, 38% of patients in group 2, and 100% of patients in group 3. CONCLUSIONWhen assessing CT scans of children with blunt orbital trauma, the orbital floor and the roof of the maxillary sinus should be carefully evaluated for fractures and soft tissue entrapment.Special attention should be paid to the alignment and shape of the IR muscle.IR muscle tethering is the most common muscle abnormality in orbital floor trapdoor fractures. CLINICAL SIGNIFICANCEOn CT, orbital floor trapdoor fractures in children may be underestimated because of the small size of the herniated tissue and the subtle nature of the bone displacement.Detailed CT findings may improve radiologists' awareness of this condition.

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