Unidentified bright objects of spleen on arterial phase CT: mimicker of splenic vascular injury in blunt abdominal trauma

PURPOSEWe have described unidentified bright objects of spleen (UBOS), a hitherto undescribed entity, as hyperdense areas on arterial phase (AP) computed tomography (CT) seen in relation to splenic lacerations and are isodense to the normal parenchyma on portal venous phase with no correlate on digital subtraction angiography (DSA). UBOS mimic splenic vascular injuries like active contrast extravasation and pseudoaneurysm and need to be differentiated from them as it would have implications on patient management. We undertook this study to identify CT features of UBOS that can differentiate them from splenic vascular injuries and to calculate their diagnostic accuracy.METHODSThis retrospective study was approved by the institutional ethical committee and the need for informed consent was waived. Patients with splenic injury who had undergone dual-phase CT and DSA were included. All the lesions that were hyperdense on AP were evaluated for their outline, their relation to the adjacent/parallel margins of a laceration (margin sign), string of beads appearance, and the presence of adjacent normal parenchyma (adjacent parenchyma sign). The Hounsfield unit (HU) of the lesion and the aorta on the AP were also noted. The diagnostic accuracy of various signs for distinguishing UBOS from splenic vascular injuries was calculated using DSA as the reference standard.RESULTSOf 48 patients, 5 were excluded due to suboptimal quality of the examination or a time difference of more than 6 hours between the CT and DSA. A total of 54 hyperdense lesions were detected on AP in 43 patients. These were classified as vascular injuries (pseudoaneurysm, n=11; active contrast extravasation, n=11) and UBOS (n=32) based on DSA. The margin sign, string of beads appearance, and ill-defined outline had high specificity (95%, 86%, and 82%, respectively) but low sensitivity (50%, 65%, and 63%, respectively). The adjacent parenchyma sign had a moderate sensitivity and specificity of 84% and 77%, respectively. ROC analysis showed that a difference of 50 HU between the aorta and the lesion had a high sensitivity and specificity of 88.9% and 90.6%, respectively, with an area under the curve of 0.90.CONCLUSIONAn attenuation difference of over 50 HU between the aorta and the lesion and the presence of normal adjacent parenchyma had the highest diagnostic accuracy, while an ill-defined outline, string of beads appearance, and margin sign had high specificity but low sensitivity for differentiating UBOS from splenic vascular injuries.

Although there is a wide variation in the computed tomography (CT) protocol for the evaluation of blunt abdominal trauma across centers, arterial phase (AP) CT is increasingly being used as part of the evaluation (1–3). AP is usually acquired as a part of whole-body (chest and abdomen) CT angiography followed by a portal venous phase (PVP) acquisition of the abdomen (4–7). AP has been shown to increase the sensitivity of CT for the detection of splenic vascular injuries like pseudoaneurysms (6–9). These appear hyperdense relative to the surrounding parenchyma on AP, leading to better detection rates on AP. However, due to poorly understood mechanisms, the splenic parenchyma shows heterogeneous enhancement in the arterial phase (10–14). This is further exaggerated in the presence of parenchymal injuries like laceration following blunt abdominal trauma leading to the appearance of hyperdense areas on AP which may masquerade as intraparenchymal pseudoaneurysms or active extravasations.We describe unidentified bright objects of spleen (UBOS) as hyperdense areas seen in relation to splenic lacerations on AP CT which are isodense to the normal parenchyma on PVP with no abnormal correlate on digital subtraction angiography (DSA). As most splenic vascular injuries are hyperdense on AP and some of them isodense on PVP, these UBOS closely mimic splenic vascular injuries (Fig. 1).Open in a separate windowFigure 1. a, bIllustration depicting the imaging features of unidentified bright objects of spleen (UBOS) and pseudoaneurysm: UBOS (a, asterisk) show ill-defined outline, normal adjacent parenchyma, string of beads appearance due to multiple adjacent lesions, the presence of lesions on adjacent/parallel margins of laceration. Also, UBOS show no communication with the arterial and is less bright than the adjacent arteries (depicting lesser HU). Pseudoaneurysm (b, asterisk) shows a well-defined lesion with no adjacent normal parenchyma in direct communication with an artery. Brown shaded area represents a laceration with intraparenchymal hematoma.The 2018 revision of the organ injury scale for splenic injuries by the American Association for Surgery in Trauma (AAST) has incorporated CT-diagnosed vascular injuries into the grading system. The grade of injury is upgraded to grade 4/grade 5 if there are associated splenic vascular injuries irrespective of the grade of parenchymal injuries (15–17). Hence, it is imperative to accurately diagnose the splenic vascular injuries on CT and to differentiate UBOS, a previously undescribed entity, from splenic vascular injuries, as it would have implications on the grading of injury and further management.There are no studies describing such an entity or its imaging features. We undertook this retrospective study to describe CT features of UBOS and to identify features that can differentiate UBOS from pseudoaneurysms or active extravasations and test their diagnostic accuracy.