Evaluation of Blunt Abdominal Trauma Using PACS-Based 2D and 3D MDCT Reformations of the Lumbar Spine and Pelvis

Transcription

1 PACS-Based MDCT Reformations of Blunt Abdominal Trauma Musculoskeletal Imaging Original Research Brian C. Lucey 1 Joshua W. Stuhlfaut Aaron R. Hochberg Jose C. Varghese Jorge A. Soto Lucey BC, Stuhlfaut JW, Hochberg AR, Varghese JC, Soto JA DOI: /AJR Received September 2, 2004; accepted after revision December 10, All authors: Department of Radiology, Division of Body Imaging, Boston University Medical Center, 88 E Newton St., Atrium 2, Boston, MA Address correspondence to B. C. Lucey (brian.lucey@bmc.org). AJR 2005; 185: X/05/ American Roentgen Ray Society Evaluation of Blunt Abdominal Trauma Using PACS-Based 2D and 3D MDCT Reformations of the Lumbar Spine and Pelvis OBJECTIVE. The purpose of this study was to show the value of 2D and 3D reformations of CT data from abdominal and pelvic CT performed immediately at the workstation using a PACS-based software program to evaluate the lumbar spine and pelvis in patients with blunt abdominal trauma. MATERIALS AND METHODS. We reviewed the abdominopelvic CT scans and conventional radiographs of the lumbar spine or pelvis of 156 consecutive patients with blunt abdominal trauma. The CT data were compared with the radiographic findings and also with the findings of dedicated repeat CT of the spine or pelvis, when performed. RESULTS. CT depicted 80 fractures of the lumbar spine and 178 pelvic fractures. Radiography showed 40 fractures of the lumbar spine and 138 pelvic fractures. No additional fractures were identified on dedicated repeat CT. CONCLUSION. Conventional radiographs to clear the lumbar spine are no longer required when abdominopelvic CT data are available. CT and reformatted CT data show more fractures than radiography and miss no fractures compared with dedicated CT of the lumbar spine or pelvis. Having these images immediately available through the PACS workstation saves time for the trauma team in the management of critically ill patients. n the United States, CT is the investigation of choice for the eval- I uation of intraabdominal injury from blunt abdominal trauma [1 4]. Early evaluation of the spine is of paramount importance in the trauma patient both to decrease patient morbidity and to decrease the length of time that the patient is on spinal precautions. It has already been established that evaluation of the cervical spine in trauma patients is better with dedicated cervical spine CT than with conventional radiography [5 11]. Indeed, in patients who have a fracture of the lumbar vertebral bodies or pelvis identified on radiography, a dedicated CT scan through the area of interest with thin collimation ( 2 mm) is traditionally requested by the orthopedic surgeons. CT through the area of interest has frequently been requested after the initial abdominal or pelvic CT examination. This is because the coronal and sagittal reformations produced by incremental CT and single-detector CT were insufficient for accurate evaluation of bone fragments in the spinal canal or hip joint. With the near ubiquitous use of MDCT in the emergency department for the evaluation of the abdomen and pelvis, a large number of thinly collimated CT images of the regions that include the lumbar spine and pelvis are generated. These images are ideally suited for multiplanar reformations and 3D volume rendering. There have been reports of using abdominal CT data to evaluate the lumbar spine [12 14]. At our institution, we routinely use MDCT images of the abdomen and pelvis to generate immediate online multiplanar and 3D reformations of the lumbar spine and pelvis at the PACS workstations. The purpose of this study was to determine whether the diagnostic performance of this approach is sufficiently high to eliminate the need for radiography of the lumbar spine and pelvis from the initial workup of multiple-trauma patients and to eliminate the need for repeat dedicated CT scans through the fracture site. Materials and Methods Patients Approval from our institutional review board was obtained. We reviewed our database of trauma cases and retrieved the records of 156 consecutive patients who underwent both abdominal or pelvic CT and radiography of the pelvis or the lumbar spine after sustaining blunt abdominal trauma (107 males and 49 females; mean age, 39 years; age range, 5 93 years) over a 9- AJR:185, December

2 A C Fig year-old man with large fracture through L5 vertebral body. A, Lateral radiograph of lumbar spine. No fracture was identified during image analysis session. B, Sagittal reformatted image of abdominopelvic CT scan shows large fracture through L5 vertebral body that was not visible on radiograph (A). C, Axial CT image shows fracture through transverse process of L4 on right that was not visible on radiograph (A). B month period (January 2002 to September 2002). All patients had radiographs of the pelvis, according to standard departmental trauma protocol. Seventy-four patients (47%) had radiographs of the lumbar spine also. In all cases, both the CT scans and radiographs were requested by the trauma team. The radiographs of the lumbar spine were ordered for patients when the trauma team believed that there was high clinical index of suspicion for lumbar spine fracture AJR:185, December 2005

3 PACS-Based MDCT Reformations of Blunt Abdominal Trauma CT All CT examinations were performed using a 4- MDCT scanner (MX 8000, Philips Medical Systems). Imaging parameters included a slice collimation of 3.2 mm reconstructed at 1.6-mm intervals, 140 kvp, and mas. IV contrast material (300 mg I/mL iohexol, 100 ml) was given in all patients at a rate of ml/sec through a 20-gauge line, ideally placed in the antecubital fossa. No oral contrast material was given according to our standard departmental trauma protocol [15]. Ten (13%) of the 74 patients had a repeat CT examination using 2-mm collimation dedicated to a segment of the lumbar spine that was considered abnormal on the initial radiographs or on the initial abdominal CT scan. Twelve (8%) of the 156 patients underwent repeat dedicated CT scanning of the pelvis using 2-mm collimation at the request of the orthopedic team. The repeat lumbar spine CT scans were ordered for evaluation of the spinal canal at the site of injury and to specifically identify bone fragments retropulsed toward the spinal canal. The repeat pelvis CT scans were ordered to evaluate for bone fragments within the hip joints. Conventional Radiography A single portable anteroposterior view of the pelvis was obtained in the trauma room on admission in all patients. Radiography of the lumbar A spine ideally included an anteroposterior view and a lateral view. Both views were obtained in 70 (95%) of 74 patients. A single view was obtained in the remaining four patients. Three of these views were lateral and one was anteroposterior. This discrepancy resulted from patient instability while obtaining the images and the second view could not be obtained. Sixty-one (82%) of the 74 patients had radiographs obtained as the initial evaluation of the lumbar spine. Thirteen (18%) of the 74 patients had radiography of the lumbar spine performed after the initial abdominal and pelvic CT examination was performed. Nine patients (12%) had repeat radiography after CT because the initial radiographs were considered inadequate for excluding a lumbar spine fracture (Figs. 1 3). Twenty-eight patients (18%) had repeat anteroposterior radiographs of the pelvis after abdominopelvic CT was performed. An additional 67 patients (43%) had repeat three-view pelvic series including anteroposterior and both 45 oblique views (Judet views) performed after the initial CT scan. These films were obtained for a more complete evaluation of the acetabula. Image Interpretation CT images were reviewed at a PACS workstation by two radiologists, by consensus. Multiplanar and B Fig year-old man with shattered lumbar vertebra. A, Radiograph obtained after abdominal CT scan shows deformity of spine, which suggests compression fractures that are difficult to define. Lateral radiograph could not be obtained because patient became unstable and was transferred to operating room. B, Sagittal reformatted image of abdominopelvic CT scan clearly shows shattered lumbar vertebra with retropulsion of bone fragments into spinal canal. 3D reconstructions were obtained in all cases. These were obtained using a software package (Voxar 3D, Voxar Inc.) that is directly incorporated into the PACS workstations. This allows immediate online postprocessing of the raw data at the primary interpreting workstation without requiring the imaging data to be transferred to a separate stand-alone workstation. For interpretation of the CT data sets, the radiologists were allowed to use the axial images displayed with bone window settings (width, 3,200 H; level, 800 H), and were asked to use the postprocessing options available (multiplanar and volume-rendering reformations) as needed. However, we did not record the number of reformations that were generated by the radiologists. Radiographs were reviewed during a separate session approximately 4 weeks after the CT interpretation on a PACS workstation by the same two radiologists who were blinded to the CT results. The presence or absence of lumbar spine and pelvic fractures was recorded for both interpretation sessions (CT scans and radiographs). Spinal fractures were divided into three groups: vertebral body fractures, transverse process fractures, and spinous process fractures. Pelvic fractures were classified and documented as involving the pubic rami, iliac bones, acetabula, and sacrum or symphysis pubis diastasis. For statistical purposes, we evaluated the kappa value between the two observers for each segment of the lumbar spine and pelvis AJR:185, December

4 A Fig year-old man with anterior wedge-compression fracture of L4. A, Lateral radiograph of lumbar spine shows mild anterior wedge-compression fracture of L4. B, Sagittal reformatted image of abdominopelvic CT scan shows fracture through anterior part of vertebral body. C, Sagittal reformatted image of abdominopelvic CT scan shows unsuspected extent of fracture involving posterior wall of vertebral body. D, Coronal reformatted image of abdominopelvic CT scan shows comminuted nature of fracture. B C D 1438 AJR:185, December 2005

5 PACS-Based MDCT Reformations of Blunt Abdominal Trauma in addition to comparing the kappa values for the total number of fractures identified. For this study, no pathologic gold standard was used because this would be impractical. For the purposes of this study, the CT scans were obtained to represent the gold standard because we believed that, given the reported reliability of MDCT, no significant fractures would be missed. If available, the repeat dedicated CT scans were also used in conjunction with the initial CT scans as a gold standard. We acknowledge the implicit limitations that this places on the study. Results Lumbar Spine On MDCT images, fractures of the lumbar spine were identified in 43 (28%) of 156 patients. A total of 80 fractures were identified that included 21 burst fractures, 57 transverse process fractures, and two spinous process fractures. Of the dedicated repeat CT scans of the lumbar spine, a total of 19 fractures were identified. These included eight burst fractures, 10 transverse process fractures, and one spinous process fracture. All of these fractures were identified on the original CT scans of the abdomen and pelvis. s were identified in 40 patients on the radiographs of the lumbar spine and included 19 burst fractures, 21 transverse process fractures, and no spinous process fractures. No fracture identified by radiography was missed by CT. Pelvis Of the 156 patients, fractures of the pelvis were identified in 82 patients (53%) using MDCT. A total of 178 fractures were identified, including 86 pubic rami fractures, 33 acetabular fractures, 19 iliac fractures, 31 sacral fractures, and nine cases of diastasis of the symphysis pubis. Of the dedicated repeat CT scans of the pelvis, a total of 19 fractures were identified. These included eight pubic rami fractures, nine acetabular fractures, and two sacral fractures. All of these fractures were TABLE 3: s of the Pelvis by Location by Observer Pubic Rami Ilium Acetabulum Sacrum Diastasis of the Symphysis Pubis Observer No No No No No κ 0.94 a 0.94 a 1.0 a 1.0 a 0.95 a 0.95 a 0.98 a 0.98 a 1.0 a 1.0 a a Kappa value indicates strength of agreement between the observers is very good. identified on the original CT scans of the abdomen and pelvis. On the radiographs of the pelvis, a total of 138 fractures were identified. These included 75 pubic rami fractures, 29 acetabular fractures, 12 iliac fractures, 13 sacral fractures, and nine cases of diastasis of the symphysis pubis. No fracture identified by radiography was missed by CT. The kappa value for the total number of fractures detected was (95% confidence interval [CI], ), and the strength of agreement between the two observers was very good (Table 1). The kappa values for the individual segments of the lumbar spine and pelvis are detailed in Tables 2 and 3, respectively. Discussion MDCT with multiplanar reconstructions and 3D reconstructions exquisitely delineates the extent of injury and yields a certainty in diagnosis when evaluating the lumbar spine and pelvis after blunt abdominal trauma [12 14]. The widespread availability of MDCT has removed many of the difficulties associated with lumbar spine and pelvis evaluation using incremental CT scanners. There has been little debate in deciding that CT is superior to radiography in the evaluation of the spine in the trauma patient [5 14]. The difficulties faced by abdominopelvic CT in replacing radiography for evaluating the lumbar spine stem primarily from the days of incremental CT scanners. These scanners would usually obtain slices through the abdomen up to 8 mm in thickness. Although this was often sufficient to identify lumbar spine fractures, precise evaluation of the fractures was difficult, particularly in deciding whether bone fragments impinged on the spinal canal or if bone fragments were present in the hip joint. In addition, multiplanar reconstructions were unsatisfactory with such thick slices. As a result, trauma and orthopedic surgeons have traditionally requested repeat CT scans through areas of known or suspected fractures seen on the abdominal CT scans obtained using thin slices, often on the order of 2 mm in thickness [16]. With the widespread use of MDCT in the evaluation of trauma patients, thin slice images are routinely obtained resulting in a large data set that is ideally suited to multiplanar reconstruction and 3D reconstruction. The reconstruction interval used is frequently smaller than the 2-mm slices previously requested by the trauma and orthopedic surgeons. This obvi- TABLE 1: Number of s by Each Observer Observer No , ,779 κ a a a Kappa value indicates strength of agreement between the observers is very good. TABLE 2: s of the Lumbar Spine by Location by Observer Vertebral Body Transverse Process Spinous Process Observer No No No κ 1.0 a 1.0 a 0.96 a 0.96 a 1.0 a 1.0 a a Kappa value indicates strength of agreement between the observers is very good. AJR:185, December

6 ates repeat dedicated thin-slice CT through the region of interest. As can be seen from our results, 10 patients had a repeat CT examination of an area of the lumbar spine for further evaluation of a lumbar spine fracture found on the abdominal CT scan. None of these images depicted new diagnostic information. In addition, 12 patients had repeat dedicated pelvic CT examinations, none of which yielded new diagnostic information. As a result, we no longer perform repeat thin-slice CT through the lumbar spine or pelvis for this purpose alone. One often touted disadvantage to performing multiplanar and 3D reconstructions routinely is the time element that is traditionally associated with it [17 19]. In most institutions, MDCT data must be sent to a dedicated 3D workstation so that these reconstructions can be performed. Given the large size of the data sets, this may take considerable time. In addition to the time taken for data transfer, the dedicated 3D workstation is not always located close to the CT interpretation workstation in the emergency department. This places an added inconvenience to using multiplanar reconstructions and 3D reconstructions. At our institution, the ability to perform reconstructions is built in to our software at the CT interpretation workstations. This means that there is no increased delay while sending images to a separate workstation. The availability of multiplanar reconstruction and 3D reconstructions is also one mouse click away. The MDCT data from abdominal CT can be converted into coronal and sagittal views of the lumbar spine in approximately sec. This results in the ability to evaluate the lumbar spine and pelvis rapidly purely on basis of the CT data derived from abdominal CT, which in turn enables faster decision making by the trauma team regarding patient management. Evaluating the lumbar spine on the basis of abdominal CT data when managing a patient in the setting of major trauma saves time in many ways. First, removing the necessity for obtaining conventional radiographs eliminates the time taken to obtain adequate images of the lumbar spine. Repeated attempts to obtain satisfactory imaging are eliminated because there is an increased certainty of diagnosis with CT. Time is also saved later by eliminating the requirement for dedicated lumbar spine CT. The patient may also be removed from spinal precautions once the spine has been cleared. If this can be done immediately, the patient benefits from increased comfort and staff do not have as much to fear from patient manipulation. There is the added benefit of decreasing the overall radiation dose to the patient by eliminating the requirement for radiography and dedicated CT. This is helpful because many major trauma patients are in the younger age group. Another consideration to removing the requirement for radiography and repeat CT comes in the form of health care cost reduction. In the current environment of fiscal rectitude, any alteration to the health care algorithms that may lead to a reduction in overall health care cost is welcome. Although we did not perform an analysis of cost for this study, the overall savings would result from performing 22 fewer dedicated CT examinations, 83 lumbar spine series (74 initial and nine repeat), 28 repeat pelvic conventional radiography examinations, and 67 three-view pelvic series. In conclusion, multiplanar reconstruction and 3D reconstruction of MDCT data of the abdomen and pelvis in patients with blunt abdominal trauma is sufficient to obviate performing radiography of the lumbar spine. Dedicated thin-collimation CT of the lumbar spine or pelvis is no longer necessary. 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