Abstract

Purpose: Although posttraumatic pneumothoraces (PTXs) are common and potentially life threatening, the supine chest radiograph (CXR) is an insensitive test for their detection. Computed tomography (CT) often identifies occult pneumothoraces (OPTXs). Previous descriptions of OPTX topography have been poor. Our purpose was to define their distribution and aid in the targeting of thoracic ultrasound. Methods: Posttraumatic supine CXRs and CTs were reviewed for occult, overt, and residual PTXs. PTXs were compared according to their apical, basal, anterior, lateral, medial, and posterior components. A comparative size index was calculated.

Results: Among 761 patients, 338 CT scans revealed 103 PTXs in 89 patients; 55% were OPTXs. OPTXs were apical (57%), basal (41%), anterior (84%), lateral (24%), and medial (27%), with 0% posterior. Conclusions: CXR missed over half of all PTXs. OPTXs had a greater anterior versus lateral (nearly 4-fold) and both basal and apical versus lateral (2-fold) distribution. OPTXs are often located at easily accessible sonographic windows.

Background

Pneumothoraces (PTXs) : the most common serious blunt chest injury notable cause of preventable death simple intervention  life saving seriously injured patients : chest PA the least sensitive of all plain radiographic techniques for showing PTXs

CXR is also inaccurate in defining the size and actual location of a PTX. up to 72% of all traumatic PTXs are first detected on a subsequent CT scan of the chest and/or abdomen.  occult pneumothorax (OPTX). ↑CT scanning as the investigation of choice for blunt thoracoabdominal trauma  OPTXs ↑.

There is a paucity of reported data outlining the precise intrathoracic distribution of either overt or occult PTXs defined by CT scan. The primary objective of this study  define the location and size of all posttraumatic PTXs.  address an increased interest in the sonographic detection of PTXs enhanced sensitivity of thoracic ultrasound over supine AP CXR in diagnosing OPTXs. precise chest topographical knowledge regarding where exactly to focus the diagnostic examination.

Material and Methods

All trauma patients (Injury Severity Score [ISS]>=12) with CXRs and CT scans of the chest and/or abdomen who presented to our adult regional trauma center between June 30, 2002, and July 1, 2003, were identified via our trauma registry.

Occult PTXs ： not visible on the supine AP CXR but were obvious on a CT scan. Overt PTXs ： obvious on supine AP CXR, even if they had not been appreciated by the resuscitating clinicians. Residual PTXs ： were defined as PTXs that had been appreciated either clinically or radiologically and thus treated with chest drainage but that had an obvious undrained collection of intrapleural air on a CT scan. Secondary OPTX ： a residual PTX that was not evident on a post– chest tube insertion AP CXR but that was later detected on a CT scan.

Each CXR was also retrospectively reviewed for secondary signs of a PTX (ie, double diaphragm, sharpened cardiac silhouette, hyperlucent hemithorax, deep sulcus, depressed diaphragm, and apical pericardial fat). Once a PTX was identified on a CT scan, its distribution was noted. Size of overt, occult, and residual PTXs was characterized by the number of 5-mm CT images.

superior to the manubrium or first rib touching the diaphragm

Result

338 of 761 (44%) trauma patients underwent a CT scan. Of these (55%) ： complete chest, abdomen, and pelvis CT 152 (45%) ： abdomen and pelvis imaging only. One patient also had a chest CT only. All patients had a supine CXR. The study group was 75.3 % male and injured by blunt trauma in 98.5% of cases. 103 PTXs were present in 89 patients.

Age, sex, ISS, and length of stay were similar between all groups, with the exception that patients with any PTX had a statistically higher ISS than those without a PTX (P _.002). 55% 49%16%35%

The varying distribution of occult, overt, and residual PTXs was not statistically different

Only 1 (2%) had any a secondary sign consistent with a missed, rather than occult, PTX. This patient had a double diaphragm sign. no difference in either the distribution or comparative size index between ventilated and nonventilated patients in the occult, overt, or residual cohorts significantly more patients with residual PTXs were intubated and ventilated.

Comments

Clinicians are often required to diagnose PTXs when treating seriously injured patients. Large symptomatic PTXs should be detected clinically and treated solely on speculation in hemodynamically unstable patients. The supine AP chest radiograph remains the initial imaging test in most stable trauma patients. The nonradiologist ： a visible pleural line / absence of lung markings double diaphragm, sharpened cardiac silhouette, hyperlucent hemithorax, deep sulcus, depressed diaphragm, and apical pericardial fat  quite subtle and often not used to diagnose PTXs.

As a result, the conventional supine AP CXR remains the most available, but least sensitive, of all plain radiographic techniques for showing PTXs Our study confirms that the majority of both OPTXs and overt PTXs are anterior in the supine patient. There was also no difference in the comparative index or number of CT images between occult and overt PTX cohorts.  This highlights the inadequacy of the supine AP CXR. Residual PTXs remaining after the insertion of a chest tube, however, were larger than either occult or overt PTXs.

“Secondary” occult PTXs ： reinforces the fact that the mere placement of a chest tube does not preclude the presence of a PTX.  thoracostomy tubes are subject to misplacement, dislodgement, obstruction, and malfunction.

The location of a PTX appears to be directly associated with the effects of gravity, elastic recoil of the lung and chest wall, and tethering of the lung itself by the hilar structures and inferior pulmonary ligament Upright ： over and lateral to the lung apices because gravity pulls the recoiling lung caudally. Supine ： unique, however, because the lung falls dorsally on the hilar hinge.  anteromedially in the least- dependent space. (no pleural adhesions or interfering traumatic thoracic injuries, )

particularly difficult to detect and quantify on supine CXR the first area to be examined in the extended focused assessment with sonography for trauma. OPTXs were twice as often apical and basal. anteromedial chest (second intercostal space in the midclavicular line) and costophrenic sulci (fourth or fifth intercostal space in the anterior axillary line),  a thoracic ultrasound ： over the areas where OPTXs are most commonly located.

With a standard CT scan of the abdomen and pelvis, OPTXs would have been missed. Although the morbidity of OPTXs is likely minimal in a nonventilated population, --> untrue in intubated patients. thoracic CT should be routine in all patients with severe blunt trauma because it is the only reliable way to safely rule out OPTXs. The distribution and size of both overt and OPTXs in the positive pressure–ventilated patients was similar to the nonintubated cohort.  particularly important because these patients may be at increased risk of progression to a tension PTX if left untreated.

Summary

the anatomic distribution of occult, overt, and residual PTXs is similar. The largest group of PTXs was those that remained after tube thoracostomy. (residual) Occult PTXs are not uncommonly seen only in the superior thorax, implying the gold standard for ruling out a PTX is thoracic CT. With a predominantly anterior topography in the supine patient, the extended focus assessment with sonography for trauma examination ： increased diagnostic sensitivity. some PTXs reside only in the thoracic apex ： sonographic window sensitive to this site may further improve its diagnostic accuracy.

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