Sagittal Computed Tomography Reconstructions Research Articles

Plain roentgenographic and CT scan morphometric analysis of the anterior atlantodens interval (AADI) and posterior atlantodens interval (PADI) in the Indian population

Background: The anterior atlantodental interval (AADI) and posterior atlantodental interval (PADI) on X-ray and computed tomography (CT) studies can both be used to gauge the risk and/or presence of neurological compression.Methods: This retrospective observational study was conducted at a tertiary care center in 116 patients with head injuries additionally warranting routine cervical X-ray and CT examinations.Results: The AADI averaged 1.36 ± 0.45 mm (X-ray) and 1.393 ± 0.47 mm (CT), while the mean PADI was 18.04 ± 2.44 mm (X-ray), and 18.07 ± 2.43 mm (CT). Notably, 93.96% of the total subjects had AADI below 2 mm. Further, 6.8% of patients with PADI =/<14 mm had no neurological deficits.Conclusion: No significant differences were observed for X-ray versus CT studies, measuring AADI and PADI. Therefore, X-rays should continue to prove reliable for assessing craniovertebral junction anatomy in emergency settings. Of interest, the normal upper limit of AADI on sagittal CT reconstructions should now be changed to 2 mm from the previously accepted upper limit of 3 mm.

Clinical impact of collateral circulation in patients with median arcuate ligament syndrome.

We aimed to analyze computed tomography (CT) findings and medical records of patients diagnosed with median arcuate ligament syndrome (MALS) and evaluate possible risk factors associated with vascular complications that develop in patients with MALS. This retrospective study was approved by the institutional review board, and the requirement to obtain informed consent was waived. A total of 37 consecutive patients were diagnosed with MALS using both axial and sagittal CT reconstruction imaging at a single institution over a 7-year period. Dynamic contrast-enhanced CT data, medical records, and angiography results were reviewed. Thirty-two (86.5%) patients were asymptomatic and incidentally diagnosed with MALS using CT. Seventeen (45.9%) patients exhibited significant arterial collateral circulations and nine (24.3%) were found to have splanchnic artery aneurysms, including one (2.7%) with acute bleeding secondary to aneurysm rupture. Peripancreatic vascular network including pancreaticoduodenal arcades and dorsal pancreatic artery was the most common site for development of both collateral circulations (16/22, 72.7%) and aneurysms (9/16, 56.3%). Splanchnic artery aneurysms were significantly more common in patients with collateral circulations (8/17, 47.1%) compared with those without collateral circulations (1/20, 5%) (P < 0.01). At least one peripancreatic vascular aneurysm was found in five of nine patients with splanchnic artery aneurysms (55.6%). Splanchnic artery aneurysms are not uncommon in asymptomatic patients with collateral circulations caused by significant celiac trunk stenosis or obstruction due to median arcuate ligament. Therefore, careful imaging evaluation is necessary in patients with peripancreatic collateral circulations associated with MALS and regular follow-up is recommended for possibility of aneurysm development and rupture. Prophylactic endovascular treatment should be specifically performed in patients with pancreaticoduodenal arcade aneurysms to prevent life-threatening aneurysm rupture regardless of size.

Minimum 5-year Follow-up Results for Occipitocervical Fusion Using the Screw-Rod System in Craniocervical Instability.

Retrospective clinical study. To evaluate the clinical outcome of patients who had undergone occipitocervical (OC) fusion using pedicle screws and rods over a minimum 5-year follow-up. Few studies have evaluated occipitocervical (OC) fusion using pedicle screws and rods for long-term follow-up. Twenty-seven consecutive patients treated underwent posterior OC fusion using pedicle screws and rods over a minimum 5-year follow-up. The Modified McCormick scale to grade a patient's functional status and the Japanese Orthopaedic Association (JOA) scoring system were used to evaluate preoperative and postoperative neurological function. We assessed fusion by both direct and indirect evidence; bony trabeculae at the graft-recipient interface on lateral cervical radiographs and sagittal computed tomography reconstruction was considered direct evidence of union. The mean follow-up period was 7.2 years (5-14 y). JOA scores were 8.1±3.8 before surgery and 11.7±3.7 at the final follow-up. The recovery rate calculated from the JOA scores was 42.0±30.0%. Functional status did improve at least 1 grade according to the modified McCormick scale in 18 patients (66.7%). There was no deterioration at the final follow-up.There were postoperative implant-related complications in 8 patients (29.6%): loosening of pedicle screws in 2, rod breakage in 2, plate breakage in 1, screw breakage in 1, pullout of pedicle screws in 1, and wiring induced myelopathy in 1 patient. The average duration between surgery and implant failure was 31.2 months (12-60 mo) except for 2. Sufficient bone grafting, proper decortication of the bone bed, using thicker and high stiffness rods, and ultra-high molecular weight polyethylene tape as a fixation or reinforcement of implant may help prevent implant failure.

Lateral Radiographic Landmarks for ACL and LCL Footprint Origins During All-Epiphyseal Femoral Drilling in Skeletally Immature Knees.

This study was conducted to evaluate the spatial relationship of the anterior cruciate ligament (ACL) and lateral collateral ligament (LCL) femoral footprint origins in knee specimens from skeletally immature donors as viewed on lateral radiographs. Fourteen cadaver specimens of skeletally immature knees from children between 7 and 11 years old at the time of death were examined through gross dissection. Metallic pins were placed at the center of the ACL and LCL femoral footprints, and computed tomography (CT) scans were performed. Sagittal plane CT images were merged to create a view analogous to an intraoperative C-arm image with overlaid ACL and LCL ligament footprints. Ligament origins were then measured as a percent of the epiphyseal depth (% P-A [posterior-anterior]) and height (% P-D [proximal-distal]). The ACL origin was centered at a point located 14% (14% P-A) of the total lateral femoral condyle (LFC) depth from the most posterior aspect of the LFC and 38% (38% P-D) of the LFC height from the most proximal aspect of the posterior physis. The LCL origin was centered at a point 27% P-A and 37% P-D. When viewed on a sagittal CT reconstruction analogous to a perfect lateral intraoperative fluoroscopic view, the ACL footprint origin is posterior and slightly inferior to the LCL origin. Both origins are distal to the distal femoral physis and are posterior to the origin of the popliteus. This study demonstrates a consistent relationship between the origin of the ACL and LCL, which may be useful in guiding safe tunnel placement during all-epiphyseal ACL reconstruction in skeletally immature knees. This anatomic reference can be used intraoperatively to guide and radiographically evaluate ACL tunnel placement while avoiding the LCL origin in skeletally immature patients.

Periaortic cutaneous fistula 10 years after type A aortic dissection

Figure 1: (A) Computed tomography (CT) axial image with contrast injection in the wound with illustration of the peri-aortic cutaneous fistula (arrow) and the aortic prosthesis. (B) Sagittal CT reconstruction demonstrating the fistula (arrow). (C) Axial CT image of the aortic prosthesis and the omentum plasty. (D) Sagittal image of the omentum plasty and no signs of a fistula. Ao: aorta; Om: omentum.

Unreported Vertebral Body Compression Fractures at Abdominal Multidetector CT

To retrospectively assess the prevalence and clinical outcomes of unreported vertebral compression fractures at abdominal computed tomography (CT). This HIPAA-compliant study had institutional review board approval; the need for informed consent was waived for this retrospective analysis. A total of 2041 consecutive adult patients (1640 women, 401 men; age range, 19-94 years) underwent both abdominal multidetector CT and dual-energy x-ray absorptiometry (DXA) within 6 months of each other between 2000 and 2007, before sagittal CT reconstructions were obtained routinely. Transverse (axial) and retrospective sagittal multidetector CT reconstructions were reviewed for the presence of moderate or severe vertebral body compression fractures of the lower thoracic and lumbar spine by using the Genant visual semiquantitative method. Twenty-six patients were excluded for evidence of pathologic fracture or for technical factors limiting compression fracture detection. Electronic medical records were reviewed for patients with moderate or severe compression fractures to determine whether the fracture was reported at prospective CT interpretation, was known previously, or was diagnosed subsequently. Correlation was made with central DXA T scores. Statistical analysis was performed with the Student t test and Fisher exact test. At least one moderate or severe vertebral body compression fracture was identified retrospectively at CT in 97 patients (mean age, 70.8 years). Fractures involved one level in 67 and multiple levels in 30 patients, for a total of 141 fractures. In 81 (84%) patients, prospective CT diagnosis was not made. Patients in whom fractures were reported prospectively were significantly older and were more likely to have a severe compression fracture (P < .05). In 52 (64%) patients with an unreported fracture, the vertebral compression fracture was not known clinically. In 18 patients, subsequent diagnosis of a compression fracture was determined by means of another imaging study (median interval, 7 months). At DXA, 39 (48%) of 81 patients with unreported vertebral body compression fractures had a nonosteoporotic T score (greater than -2.5). Most clinically important vertebral body compression fractures in nontrauma patients at risk for low bone mineral density may go unreported at abdominal multidetector CT if sagittal reconstructions are not routinely evaluated.

Osteoporosis imaging: state of the art and advanced imaging.

Osteoporosis is becoming an increasingly important public health issue, and effective treatments to prevent fragility fractures are available. Osteoporosis imaging is of critical importance in identifying individuals at risk for fractures who would require pharmacotherapy to reduce fracture risk and also in monitoring response to treatment. Dual x-ray absorptiometry is currently the state-of-the-art technique to measure bone mineral density and to diagnose osteoporosis according to the World Health Organization guidelines. Motivated by a 2000 National Institutes of Health consensus conference, substantial research efforts have focused on assessing bone quality by using advanced imaging techniques. Among these techniques aimed at better characterizing fracture risk and treatment effects, high-resolution peripheral quantitative computed tomography (CT) currently plays a central role, and a large number of recent studies have used this technique to study trabecular and cortical bone architecture. Other techniques to analyze bone quality include multidetector CT, magnetic resonance imaging, and quantitative ultrasonography. In addition to quantitative imaging techniques measuring bone density and quality, imaging needs to be used to diagnose prevalent osteoporotic fractures, such as spine fractures on chest radiographs and sagittal multidetector CT reconstructions. Radiologists need to be sensitized to the fact that the presence of fragility fractures will alter patient care, and these fractures need to be described in the report. This review article covers state-of-the-art imaging techniques to measure bone mineral density, describes novel techniques to study bone quality, and focuses on how standard imaging techniques should be used to diagnose prevalent osteoporotic fractures.

This Month inRadiology

Osteoporosis is becoming an increasingly important public health issue, and effective treatments to prevent fragility fractures are available. Osteoporosis imaging is of critical importance in identifying individuals at risk for fractures who would require pharmacotherapy to reduce fracture risk and also in monitoring response to treatment. Dual x-ray absorptiometry is currently the state-of-the-art technique to measure bone mineral density and to diagnose osteoporosis according to the World Health Organization guidelines. Motivated by a 2000 National Institutes of Health consensus conference, substantial research efforts have focused on assessing bone quality by using advanced imaging techniques. Among these techniques aimed at better characterizing fracture risk and treatment effects, high-resolution peripheral quantitative computed tomography (CT) currently plays a central role, and a large number of recent studies have used this technique to study trabecular and cortical bone architecture. Other techniques to analyze bone quality include multidetector CT, magnetic resonance imaging, and quantitative ultrasonography. In addition to quantitative imaging techniques measuring bone density and quality, imaging needs to be used to diagnose prevalent osteoporotic fractures, such as spine fractures on chest radiographs and sagittal multidetector CT reconstructions. Radiologists need to be sensitized to the fact that the presence of fragility fractures will alter patient care, and these fractures need to be described in the report. This review article covers state-of-the-art imaging techniques to measure bone mineral density, describes novel techniques to study bone quality, and focuses on how standard imaging techniques should be used to diagnose prevalent osteoporotic fractures.

Osteoporosis Imaging: State of the Art and Advanced Imaging

Osteoporosis is becoming an increasingly important public health issue, and effective treatments to prevent fragility fractures are available. Osteoporosis imaging is of critical importance in identifying individuals at risk for fractures who would require pharmacotherapy to reduce fracture risk and also in monitoring response to treatment. Dual x-ray absorptiometry is currently the state-of-the-art technique to measure bone mineral density and to diagnose osteoporosis according to the World Health Organization guidelines. Motivated by a 2000 National Institutes of Health consensus conference, substantial research efforts have focused on assessing bone quality by using advanced imaging techniques. Among these techniques aimed at better characterizing fracture risk and treatment effects, high-resolution peripheral quantitative computed tomography (CT) currently plays a central role, and a large number of recent studies have used this technique to study trabecular and cortical bone architecture. Other techniques to analyze bone quality include multidetector CT, magnetic resonance imaging, and quantitative ultrasonography. In addition to quantitative imaging techniques measuring bone density and quality, imaging needs to be used to diagnose prevalent osteoporotic fractures, such as spine fractures on chest radiographs and sagittal multidetector CT reconstructions. Radiologists need to be sensitized to the fact that the presence of fragility fractures will alter patient care, and these fractures need to be described in the report. This review article covers state-of-the-art imaging techniques to measure bone mineral density, describes novel techniques to study bone quality, and focuses on how standard imaging techniques should be used to diagnose prevalent osteoporotic fractures.

Computed Tomography of the Ankle in Full Plantar Flexion: A Reliable Method for Preoperative Planning of Arthroscopic Access to Osteochondral Defects of the Talus

The purpose of this study was to determine whether preoperative computed tomography (CT) of the ankle joint in full plantar flexion is a reliable and accurate tool to determine the anterior arthroscopic accessibility of talar osteochondral defects (OCDs). Twenty consecutive patients were prospectively studied. All patients had an OCD of the talar dome and had a preoperative CT scan of the affected ankle in maximum plantar flexion. Accessibility of the OCD was defined by the distance between the anterior border of the OCD and the anterior distal tibial rim. This distance was measured on sagittal CT reconstructions by 2 investigators. The reference standard was the distance between the same landmarks measured during anterior ankle arthroscopy by an orthopaedic surgeon blinded to the CT scans. Intraobserver and interobserver reliability of CT, as well as the correlation and agreement between CT and arthroscopy, were calculated. The measured distance between the anterior border of the OCD and the anterior distal tibial rim ranged from -3.1 to 9.1 mm on CT and from -3.0 to 8.5 mm on arthroscopy. The intraobserver and interobserver reliability of the measurements made on CT scans (intraclass correlation coefficients >0.99, P < .001), as well as the correlation between CT and arthroscopy, were excellent (r = 0.98, P < .001). Measurements on CT scans of the ankle in full plantar flexion are a reliable and accurate preoperative method to determine the in situ arthroscopic location of talar OCDs.

Reliability and Clinical Importance of Teardrop Angle Measurement in Intra-articular Distal Radius Fracture

The teardrop angle (TDA) is a newly characterized radiographic parameter that some authors propose as an indicator of articular incongruity of the lunate facet. The purposes of this study were to investigate intra-observer and interobserver reliability of the measurements of the TDA and to determine whether the TDA is a reliable indicator of articular step and gap formation after distal radius fracture. We studied radiographs of 24 uninjured wrists and 24 wrists with intra-articular distal radius fractures. On standard and 10° tilt views of lateral wrist radiographs, the teardrop represents the volar rim of the lunate facet, and the TDA is defined as the angle between the central axis of the teardrop and the radial shaft. We examined interobserver and intra-observer reliability for 3 observers using the intraclass correlation coefficient (ICC) for measurements of the uninjured and fractured wrists. For subjects with fractures, we determined correlation of the TDA-volar tilt with the articular step and gap measured by computed tomography using simple linear regression. There was almost perfect intra-observer (ICC = 0.95) and interobserver (ICC = 0.93) reliability in the fractured wrists. We observed substantial intra-observer (ICC = 0.64) and fair interobserver (ICC = 0.28) reliability in the uninjured wrists on the standard lateral radiographs. On the 10° tilt views, intra-observer and interobserver reliability in the uninjured wrists increased to substantial levels (ICC = 0.76 and 0.61, respectively). The TDA-volar tilt was significantly associated with articular step and gap on computed tomography. The TDA, measured on the lateral radiograph of the wrist, exhibits higher intra-observer and interobserver reliability in fractured wrists compared with uninjured wrists. On the 10° tilt views, the reliability increased in the uninjured wrists. Measurement of the TDA in plain radiographs may allow direct estimation of articular incongruity as seen on sagittal computed tomography reconstruction images.

Recurrent anterior shoulder instability: accuracy of estimations of glenoid bone loss with computed tomography is insufficient for therapeutic decision-making

To evaluate the reliability of glenoid bone loss estimations based on either axial computed tomography (CT) series or single sagittal ("en face" to glenoid) CT reconstructions, and to assess their accuracy by comparing with actual CT-based bone loss measurements, in patients with anterior glenohumeral instability. In two separate series of patients diagnosed with recurrent anterior glenohumeral instability, glenoid bone loss was estimated on axial CT series and on the most lateral sagittal (en face) glenoid view by two blinded radiologists. Additionally, in the second series of patients, glenoid defects were measured on sagittal CT reconstructions by an independent observer. In both series, larger defects were estimated when based on sagittal CT images compared to axial views. In the second series, mean measured bone loss was 11.5% (SD = 6.0) of the total original glenoid area, with estimations of 9.6% (SD = 7.2) and 7.8% (SD = 4.2) for sagittal and axial views, respectively. Correlations of defect estimations with actual measurements were fair to poor; glenoid defects tended to be underestimated, especially when based on axial views. CT-based estimations of glenoid bone defects are inaccurate. Especially for axial views, there is a high chance of glenoid defect underestimation. When using glenoid bone loss quantification in therapeutic decision-making, measuring the defect instead of estimating is strongly advised.

Lunate–Lunate Facet Ratio and Variance to Predict Articular Gap After Distal Radius Fracture

Intra-articular gap is a well-defined prognosticator of outcome after distal radius fracture. However, it is often difficult to assess on plain radiographs, particularly in the sagittal plane, as visualized on the lateral view. The purposes of this study were to establish normal values for the lunate-lunate facet ratio (LLFR) and to evaluate whether the LLFR and lunate-lunate facet variance (LLFV) are reliable plain film measures of sagittal articular gap in distal radius fractures compared with sagittal reconstructions of computed tomography (CT) scans. We studied 35 uninjured, skeletally mature wrist radiographs to establish the normal LLFR value. The LLFR was defined as the ratio of the maximum width of the lunate (A) to the width of a line spanning the maximum distance from dorsal to volar across the articular surface of the lunate facet, defined by the end point of the radiographically thickened line representing the subchondral bone (B). The LLFV was determined as measurement B minus measurement A. Interobserver and intraobserver reliability for 2 observers were examined by the intraclass correlation coefficient (ICC) for measurements of the uninjured wrists and for the same measurements of 20 intra-articular distal radius fractures. For 12 of the subjects with fractures, the LLFR and LLFV were correlated with the intra-articular gap as measured on CT scan using simple linear regression. The mean value of the LLFR in the normal subjects was 1.00 +/- 0.04 for observer 1 and 1.00 +/- 0.02 for observer 2. There was significant intraobserver reliability for both uninjured (ICC = 0.83, p < .001) and fractured wrists (ICC = 0.87, p < .001), as well as significant interobserver reliability for uninjured (ICC = 0.69, p < .001) and fractured wrists (ICC = 0.64, p = .015). The LLFR was significantly associated with articular gap on sagittal CT reconstructions (R(2) = -0.81, p < .01). The LLFV correlated highly with articular gap on sagittal CT reconstructions (R(2) = 0.83, p < .01). The LLFR, measured on the lateral radiograph of the wrist, exhibits high intraobserver and interobserver reliability, with a normal value of 1.0. Both the LLFR and the LLFV are significantly related to articular gap on sagittal CT reconstruction images. The LLFR decreases with increasing intra-articular gap formation. The LLFV allows a direct estimation of articular gap size. Diagnostic III.

Anatomic Boundaries of the Clinical Target Volume (Prostate Bed) After Radical Prostatectomy

We sought to derive and validate an interdisciplinary consensus definition for the anatomic boundaries of the postoperative clinical target volume (CTV, prostate bed). Thirty one patients who had planned for radiotherapy after radical prostatectomy were enrolled and underwent computed tomography and magnetic resonance imaging (MRI) simulation prior to radiotherapy. Through an iterative process of consultation and discussion, an interdisciplinary consensus definition was derived based on a review of published data, patterns of local failure, surgical practice, and radiologic anatomy. In validation, we analyzed the distribution of surgical clips in reference to the consensus CTV and measured spatial uncertainties in delineating the CTV and vesicourethral anastomosis. Clinical radiotherapy plans were retrospectively evaluated against the consensus CTV (prostate bed). Anatomic boundaries of the consensus CTV (prostate bed) are described. Surgical clips (n = 339) were well distributed throughout the CTV. The vesicourethral anastomosis was accurately localized using central sagittal computed tomography reconstruction, with a mean +/- standard deviation uncertainty of 1.8 +/- 2.5 mm. Delineation uncertainties were small for both MRI and computed tomography (mean reproducibility, 0-3.8 mm; standard deviation, 1.0-2.3); they were most pronounced in the anteroposterior and superoinferior dimensions and at the superior/posterior-most aspect of the CTV. Retrospectively, the mean +/- standard deviation CTV (prostate bed) percentage of volume receiving 100% of prescribed dose was only 77% +/- 26%. We propose anatomic boundaries for the CTV (prostate bed) and present evidence supporting its validity. In the absence of gross recurrence, the role of MRI in delineating the CTV remains to be confirmed. The CTV is larger than historically practiced at our institution and should be encompassed by a microscopic tumoricidal dose.

Method to plan, administer, and verify supine craniospinal irradiation.

Craniospinal irradiation remains an important technique in the management of malignancies of the central nervous system. It is technically demanding, with potential for treatment field overlap or gaps to yield unacceptable dosimetric heterogeneity. A method to accurately simulate and verify the three‐field junction is described. We use a comfortable supine position to minimize patient movement. The supine position provides airway access by anesthesiology in patients requiring sedation or anesthesia. Virtual simulation is performed with a dedicated computed tomography (CT) simulator. Multiplanar sagittal and coronal CT reconstructions allow visual confirmation of three‐field matching at the cervical region. The placement of isocenters for each field, table position, and collimator angles are determined by calculation of field sizes accommodating for beam divergence. At treatment, exact matching of the three fields is assured using the record and verify confirmation of beam collimator settings and rotation, digital couch readouts, and gantry parameters. Mini‐verification silver halide (Kodak XV) films (6×6cm) are placed behind the patient's neck and are exposed by all treatment fields (posterior flash from the lateral cranial fields and entrance from the PA spine field). These films assess field placement accuracy at the junction of these three fields. Finally, placement of radio‐opaque markers at the junction is visualized in each clinical portal radiograph. Patients readily accept the supine position as their treatment setup is eased. Field placement using digital couch settings is efficient and accurate. Daily mini‐verification films are simple, inexpensive, and allow verification of each treatment field matching. Field placement errors of greater than 1 mm can be readily identified and corrected at subsequent treatment sessions. Virtual simulation and direct junction verification with mini‐verification films allow for simple and quantitative evaluation of the junction associated with the three‐field craniospinal irradiation technique. The supine patient position does not present any difficulties in field matching or verification.PACS number(s): 87.53.–j, 87.53.–j

Craniocervical junction subarachnoid hemorrhage associated with atlanto-occipital dislocation.

The sensitivity of plain radiographs for diagnosing traumatic atlanto-occipital dislocation and its association with craniocervical junction subarachnoid hemorrhage was examined in a retrospective review of seven patients. The purpose of this study was to demonstrate the frequency of nondiagnostic plain radiographs and the common association of craniocervical junction subarachnoid hemorrhage in the context of reported cases of atlanto-occipital dislocation to facilitate better recognition of this injury. The use of sagittal reconstructions of computed tomography or sagittal magnetic resonance imaging for diagnosis was evaluated. Although traumatic atlanto-occipital dislocation is a common cause of motor vehicle fatalities, survival has been more common in the last 16 years. However, the diagnosis was missed on lateral cervical radiographs in 38% of children and 59% of adults; fewer than half were diagnosed subsequently with plain radiography. Moreover, the diagnosis of traumatic atlanto-occipital dislocation often was not considered, because more than half of the survivors had no neurologic abnormality or unilateral deficit. Consequently, more than one third of initially undiagnosed patients experienced neurologic deterioration due to inadequate cervical immobilization. Additional radiographic studies allowing diagnosis were prompted by the neurologic worsening. The authors reviewed seven patients treated with traumatic atlanto-occipital dislocation during a 14-year period. Emergency department records were compared with reexamination of initial cervical radiographs to determine the success in diagnosis by means of published methods. The frequency of cranio-cervical junction subarachnoid hemorrhage on computed tomography was determined, and the use of sagittal imaging for subsequent diagnosis was evaluated. In the emergency department, only one patient's condition was diagnosed as atlanto-occipital dislocation. Review of the initial radiographs identified an additional four patients for whom atlanto-occipital dislocation could be diagnosed. Sagittal computed tomography reconstruction or sagittal magnetic resonance imaging identified the remaining two. All but one patient had craniocervical junction subarachnoid hemorrhage. A review of reported cases revealed a common association of craniocervical junction subarachnoid hemorrhage with traumatic atlanto-occipital dislocation but not with traumatic head injury. The diagnosis of traumatic atlanto-occipital dislocation is often missed in the emergency department, and current methods for evaluating the integrity of the atlanto-occipital joint on cervical radiographs fail to identify all patients with this injury. Although infratentorial subarachnoid hemorrhage is uncommon in traumatic head injury, craniocervical junction subarachnoid hemorrhage is often associated with atlanto-occipital dislocation and should raise the suspicion of severe craniocervical ligamentous injury. Sagittal computed tomography reconstructions or sagittal magnetic resonance imaging can allow for the diagnosis when plain radiography is inconclusive.