A Clue Supporting a Diagnosis of Atlanto-Occipital Dislocation Based on a Traumatic Vacuum Phenomenon

Abstract

Sir, The high spatial and densitometric resolution of computed tomography (CT) means that it frequently shows gas (vacuum phenomenon [VP]) in tissues. VP is observed at locations that experience traumatic impact; thus, an analysis of VP may be useful for elucidating the mechanism of injury.[1] The mechanism responsible for the formation of VP is as follows: if an enclosed tissue space is allowed to expand as a rebound phenomenon after an external impact, the volume within the enclosed space will increase. In the setting of expanding volume, the pressure within the space will decrease. The solubility of the gas in the enclosed space will decrease as the pressure of the space decreases. Decreased solubility allows a gas to leave a solution. We herein report a patient in whom VP was detected near the foramen magnum after blunt trauma that resulted in a successful diagnosis of atlanto-occipital dislocation. The patient was a 53-year-old man who suddenly crashed while motorcycling on a passing lane of a national route. He was thrown from the vehicle and hit a guardrail on the median. At 16 min from the first call, emergency medical technicians reached him. He was in cardiac arrest at the time, and the initial rhythm was asystole. Bystander basic life support was absent. He was bleeding from the nose and mouth. He was transported to the grounds of a nearby elementary school and evacuated by a physician-staffed helicopter. On arrival, he remained in cardiac arrest. He underwent resuscitative thoracotomy, but it failed to obtain the return of spontaneous circulation. Autopsy CT showed subarachnoid hemorrhaging at the basal cistern and posterior fossa. A sagittal view of the skull and cervical bone on CT did not show any fracture or dislocation. However, he had several small gas densities at the deep neck area near the posterior foramen magnum [Figure 1], so the complication of atlanto-occipital dislocation was suspected. Autopsy imaging of magnetic resonance imaging showed atlanto-occipital dislocation compressing the junction between the medulla and spinal cord [Figure 1]. Figure 1 Sagittal view of computed tomography (CT, left and middle) with bony field and magnetic resonance imaging (MRI, short-tau inversion recovery image) on arrival. The CT showed several small gas densities (white triangle) at the deep neck area near the posterior foramen magnum without fracture or dislocation. MRI showed atlanto-occipital dislocation (black triangle) compressing the junction between the medulla and spinal cord. The airway was shifted frontally by a hematoma (star). CT: Computed tomography, MRI: Magnetic resonance imaging This is the first case report, wherein VP near the foramen magnum was a clue supporting a diagnosis of atlanto-occipital dislocation. The diagnosis of atlanto-occipital dislocation by imaging is not easy, and indeed, one report showed no correct diagnoses of atlanto-occipital dislocation when patients were in cardiac arrest.[2 3] Overlooking atlanto-occipital dislocation can result in a fatal outcome.[4] Accordingly, physician should strongly suspect the complication of atlanto-occipital dislocation when patients have traumatic VP near the foramen magnum on CT. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent form. In the form, the patient’s family has given his consent for his image and other clinical information to be reported in the journal. The patient’s family understands that his name and initial will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed. Research quality and ethics statement The authors followed applicable EQUATOR Network (https://www.equator-network.org/) guidelines, notably the CARE guideline, during the conduct of this report. Financial support and sponsorship This work was supported in part by a Grant-in-Aid for Special Research in Subsidies for ordinary expenses of private schools from The Promotion and Mutual Aid Corporation for Private Schools of Japan. Conflicts of interest There are no conflicts of interest.