Subsegmental pulmonary embolism diagnosed by computed tomography: incidence and clinical implications. A systematic review and meta‐analysis of the management outcome studies

Summary. Background: Multiple‐detectors computed tomographic pulmonary angiography (CTPA) has a higher sensitivity for pulmonary embolism (PE) within the subsegmental pulmonary arteries as compared with single‐detector CTPA. Multiple‐detectors CTPA might increase the rate of subsegmental PE diagnosis. The clinical significance of subsegmental PE is unknown. We sought to summarize the proportion of subsegmental PE diagnosed with single‐ and multiple‐detectors CTPA and assess the safety of diagnostic strategies based on single‐ or multiple‐detectors CTPA to exclude PE. Patients and methods: A systematic literature search strategy was conducted using MEDLINE, EMBASE and the Cochrane Register of Controlled Trials. We selected 22 articles (20 prospective cohort studies and two randomized controlled trials) that included patients with suspected PE who underwent a CTPA and reported the rate of subsegmental PE. Two reviewers independently extracted data onto standardized forms. Results: The rate of subsegmental PE diagnosis was 4.7% [95% confidence interval (CI): 2.5–7.6] and 9.4 (95% CI: 5.5–14.2) in patients that underwent a single‐ and multiple‐detectors CTPA, respectively. The 3‐month thromboembolic risks in patients with suspected PE and who were left untreated based on a diagnostic algorithm including a negative CTPA was 0.9% (95% CI: 0.4–1.4) and 1.1% (95% CI: 0.7–1.4) for single‐ and multiple‐detectors CTPA, respectively. Conclusion: Multiple‐detectors CTPA seems to increase the proportion of patients diagnosed with subsegmental PE without lowering the 3‐month risk of thromboembolism suggesting that subsegmental PE may not be clinically relevant.     

Safety of ruling out acute pulmonary embolism by normal computed tomography pulmonary angiography in patients with an indication for computed tomography: systematic review and meta-analysis

Introduction : Several outcome studies have ruled out acute pulmonary embolism (PE) by normal computed tomography pulmonary angiography (CTPA). We performed a meta-analysis in order to determine the safety of this strategy in a specific group of patients with a strict indication for CTPA, that is, 'likely' or 'high' clinical probability for PE, an elevated D-dimer concentration, or both. Methods : Studies that ruled out PE by normal CTPA, with or without subsequent normal bilateral compression ultrasonography (CUS), in patients with a strict indication for CTPA, were searched for in Medline, EMBASE, Web of Science and the Cochrane dataset. The primary endpoint was the occurrence of (fatal) venous thromboembolism (VTE) in a 3-month follow-up period. Results : Three studies were identified that excluded PE by CTPA alone (2020 patients), and three studies that performed additional CUS of the legs after normal CTPA (1069 patients). The pooled incidence of VTE at 3 months was 1.2% [95% confidence interval (CI) 0.8–1.8] based on a normal CTPA result as a sole test, and 1.1% (95% CI 0.6–2.0) based on normal CTPA and negative CUS findings, resulting in negative predictive values of 98.8% (95% CI 98.2–99.2) and 98.9% (95% CI 98.0–99.4), respectively. This compares favorably with the VTE failure rate after normal pulmonary angiography (1.7%, 95% CI 1.0–2.7). The risk of fatal PE did not differ between the diagnostic strategies (0.6% vs. 0.5%). Conclusion : A normal CTPA result alone can safely exclude PE in all patients in whom CTPA is required to rule out this disease. There is no need for additional ultrasonography to rule out VTE in these patients.     

Accuracy of single-detector spiral CT in the diagnosis of pulmonary embolism: a prospective multicenter cohort study of consecutive patients with abnormal perfusion scintigraphy.

BACKGROUND: Spiral computed tomography (CT) has emerged as a potentially conclusive diagnostic test to exclude pulmonary embolism (PE) in patients with non-high probability scintigraphy and is already widely used-sometimes as the sole primary diagnostic test in the diagnosis of suspected PE. Its true sensitivity and specificity has, however, not been evaluated previously in a large cohort of consecutive patients. METHODS: In a multicenter prospective study 627 consecutive patients with clinically suspected PE were studied. Patients with normal perfusion scintigraphy were excluded from further analysis. Single-detector spiral CT scanning and ventilation scintigraphy were then performed in all patients to diagnose PE, while pulmonary angiography was performed as the gold standard. The only exceptions were those patients who had both a high-probability VQ scan and a CT scan positive for PE: these patients were considered to have PE and did not undergo additional pulmonary angiography. All imaging tests were read by independent expert panels. RESULTS: Five hundred and seventeen patients were available for complete analysis. The prevalence of PE was 32%. Spiral CT correctly identified 88 of 128 patients with PE, and 92 of 109 patients without PE, for a sensitivity and specificity of 69%[95% confidence interval (CI) 63-75] and 84% (95% CI 80-89), respectively. The sensitivity of spiral CT was 86% (95% CI 80-92) for segmental or larger PE and 21% (95% CI 14-29) in the group of patients with subsegmental PE. CONCLUSION: The overall sensitivity of spiral CT for PE is too low to endorse its use as the sole test to exclude PE. This holds true even if one limits the discussion to patients with larger PE in segmental or larger pulmonary artery branches. We conclude that, in patients with clinically suspected PE and an abnormal perfusion scintigraphy, single-slice detector spiral CT is not sensitive enough to be used as the sole test to exclude PE.     

Computed tomography pulmonary angiography in the diagnosis of acute pulmonary embolism in the emergency department

This study was undertaken to evaluate the use of computed tomography pulmonary angiography (CTPA) in patients with pulmonary embolism (PE) who were followed in the emergency department (ED). The files and computer records of 850 patients older than 16 years of age who were seen in the Hacettepe University Hospital ED between April 10, 2001, and December 1, 2005, and who required CTPA for PE prediagnosis and/or another diagnosis, were studied retrospectively. PE was identified by CTPA in 9.4% of 416 women and in 5.8% of 434 men. A significant difference (P< .05) was noted in the women and men in whom PE was detected. The mean age of the patients was 58.13±17.88 y (range, 16–100 y). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for clinical susceptibility to PE among patients who underwent CTPA were assessed at 95.3%, 48.2%, 13%, and 99.2%, respectively. CTPA was done for different reasons: aortic aneurysm dissection (n=1), cough distinctive diagnosis (n=1), dyspnea distinctive diagnosis (n=6), chest pain distinctive diagnosis (n=3), PE prediagnosis (n=51), and other reasons (n=2). Also, sensitivity, specificity, PPV, and NPV were found to be 95.4%, 16.2%, 14.4%, and 96%, respectively, for D-dimer. CTPA, which is accessible on a 24-h basis in the ED, is a valuable tool for the diagnosis of PE.     

肺栓塞的多层螺旋CT诊断和溶栓治疗效果评价

目的探讨多层螺旋CT在肺动脉栓塞诊断和溶栓治疗效果评估中的作用。方法对52例临床拟诊肺动脉栓塞的患者行16层螺旋CT肺动脉成像(CTPA)检查,并对其中20例经溶栓治疗2周后的患者进行同机同条件复查。结果52例中8例肺动脉成像未见异常,1例为动静脉瘘,5例诊断为肺动脉高压,38例诊断肺动脉栓塞。38例肺栓塞中共累及各级肺动脉236处,其中肺动脉干5支,左右肺动脉30支,叶动脉81支,肺段动脉103支,亚段动脉17支。20例经溶栓治疗后复查,病灶均不同程度缩小或消失。结论16层螺旋CT能及时发现和诊断肺栓塞,也可指导溶栓治疗及评价疗效。     

Contrast nephropathy following computed tomography angiography of the chest for pulmonary embolism in the emergency department

OBJECTIVE: To estimate the frequency of contrast nephropathy after computed tomography angiography (CTA) to rule out pulmonary embolism (PE) in the emergency department (ED) setting. METHODS: We prospectively followed patients undergoing CTA for PE, while in the ED, for 45 days. Patients who refused follow-up or were receiving hemodialysis were excluded. Severe renal failure was defined as an increase in creatinine > or = 3.0 mg dL(-1) or a need for hemodialysis within the follow-up period. Patients were also followed for laboratory-defined contrast nephropathy, defined as an increase in creatinine of > 0.5 mg dL(-1) or > 25%, within seven days following CTA. RESULTS: A total of 1224 patients were followed, and 354 [29%, 95% confidence interval (CI): 26-32%] patients had paired (preCTA and post-CTA) creatinine measurements. None developed renal failure (0/1224; 0%, CI: 0-0.3%). 44 patients developed laboratory-defined contrast nephropathy, corresponding to an overall frequency of 4% (44/1224; CI: 3-5%) and 12% (44/354; 95% CI: 9-16%) among those with paired creatinine measurements. CONCLUSIONS: Following CTA for PE, the incidence of severe renal failure was very low, but the incidence of laboratory-defined contrast nephropathy (4% overall and 12% of those with paired measurements) was higher than expected.     

Diagnosis and management of subsegmental pulmonary embolism

Summary. Introduction: Although the advent of multi‐detector row computed tomography (CT) has enabled better visualization of subsegmental pulmonary (SSP) arteries, SSP embolism is of uncertain clinical significance. We aimed at answering the following questions: Is spiral CT an accurate method to detect SSP embolism? How are subsegmental perfusion defects managed in outcome studies including spiral CT? What are the main characteristics and outcomes of patients in whom CT detects isolated subsegmental defects? Methods: We performed a Medline search on July 1, 2004, using the keywords ‘pulmonary embolism’ and ‘computed tomography’. We limited our search to English language prospective studies comparing CT to pulmonary angiography, and to prospective outcome studies including CT in a diagnostic strategy, with at least a 3‐month follow‐up. Results: Fourteen studies comparing CT to pulmonary angiography, and five prospective management studies using CT were retrieved. The sensitivity of single‐detector CT for detecting subsegmental defects compared with pulmonary angiography was low (25%). The proportion of isolated SSP images was significantly higher in management studies using multi‐detector CT (17 of 770 scans, 2.2%) compared with those using single‐detector CT (22 of 2232, 1.0%; P = 0.01). No straightforward attitude regarding anticoagulation therapy for isolated subsegmental defects emerged from the available literature. Finally, important clinical differences were found between patients having subsegmental and segmental or more proximal defects. Conclusions: These findings underline the uncertainty regarding the clinical significance of SSP embolism, and the management of patients with such findings.     

Use of spiral computed tomography contrast angiography and ultrasonography to exclude the diagnosis of pulmonary embolism in the emergency department

Spiral computed tomography (CT) contrast angiography is a promising imaging modality for the diagnosis of pulmonary embolism but the negative predictive value of this test remains controversial. We performed a multi-center prospective cohort study to determine the safety of relying on a negative spiral CT contrast angiography scan to exclude pulmonary embolism. Patients presenting to the Emergency Departments of three tertiary care institutions with clinically suspected pulmonary embolism were potentially eligible for the study. Patients underwent a clinical evaluation to categorize pretest probability into low, moderate, and high categories, and had D-dimer testing performed. Patients at low pretest probability with normal D-dimer were considered to have pulmonary embolism excluded. The remaining patients underwent spiral CT contrast angiography scan of the pulmonary arterial circulation and bilateral venous ultrasound of the proximal leg veins. Patients who were confirmed to have pulmonary embolism or deep vein thrombosis were treated with anticoagulant therapy. Patients in whom the diagnosis of pulmonary embolism was excluded did not receive anticoagulant therapy and were followed for a 3-month period for the development of venous thromboembolic complications. Eight hundred fifty-eight (858) patients were enrolled in this study. Three-hundred sixty-nine (369) patients had low pretest probability and negative D-dimer results and no further diagnostic tests were performed. None of these patients subsequently developed venous thromboembolic complications (0%, 95% confidence interval [CI] 0% to 1.0%). The remaining 489 were referred for spiral CT contrast angiography scan and ultrasound. Sixty-seven patients were confirmed to have pulmonary embolism and an additional 15 patients with negative CT scans had proximal deep vein thrombosis (DVT) on ultrasound for a total prevalence of venous thromboembolism of 82/489 (16.8%). Two of 409 patients who had pulmonary embolism excluded in the initial evaluation phase developed proximal venous thromboembolism (0.5%; 95% CI 0% to 1.8%) in the 3-month follow-up period. These findings suggest that the combination of a negative spiral CT contrast angiography scan and normal venous ultrasound imaging safely excludes the diagnosis of pulmonary embolism in the Emergency Department setting.     

双源螺旋CT三种扫描模式肺动脉造影诊断肺栓塞

目的 比较双源螺旋CT双能量模式（DE）、单能量模式（SE）和单能量低kV（SE_LOW）3种模式下CT肺动脉造影（CTPA）图像质量、辐射剂量和肺动脉栓子分布的差异。方法 将130例临床疑诊肺动脉栓塞（PE）而接受CTPA患者随机分为DE组（43例）、SE组（42例）和SE_LOW组（45例）;评价图像质量,分析主观评分的观察者间一致性;比较3组扫描长度、扫描时间、剂量长度乘积（DLP）、容积CT剂量指数（CTDIvol）和有效剂量（ED）,以及各组非PE患者肺动脉干及各段肺动脉CT值、平均肺动脉信号噪声比（SNR）和对比噪声比（CNR）、肺动脉与邻近血管（各段肺静脉及上腔静脉、主动脉）相对密度比及肺动脉栓子分布的差异。结果 各组图像质量主观评分均以2、3级为主,未见0级病例。DE组检查时间长于SE组和SE_LOW组（P均<0.05）,SE_LOW组ED显著低于DE组和SE组（P均<0.001）,后2组差异无统计学意义（P<0.05）。SE_LOW组非PE患者肺动脉CT值高于DE组和SE组（P均<0.05）,后2组之间差异无统计学意义（P>0.05）;SE_LOW组SNR和CNR均高于SE组（P均<0.05）,DE组与SE组差异均无统计学意义（P>0.05）。3组肺动脉与邻近血管相对密度比差异均无统计学意义（P均>0.05）。对47例PE共检出262个栓子,包括DE组17例112个、SE组11例64个及SE_LOW组19例86个;使用DE Vessels&PBV亚组对肺段以下肺栓子的检出率高于不使用亚组（P<0.05）。结论 SE_LOW CTPA的 SNR和CNR较高,辐射剂量较低,能满足诊断PE需求;DE CTPA对诊断肺段以下PE具有重要价值。     

光谱CT肺动脉成像定性诊断肺动脉栓塞及定量评估肺组织灌注

目的 观察光谱CT肺动脉成像(SCTPA)定性诊断肺动脉栓塞(PE)和定量评估肺组织灌注的价值。方法 回顾性分析37例临床诊断PE患者的CTPA资料,观察常规CTPA及SCTPA后处理图像,后者包括40 keV虚拟单能量图(VMI_{40 keV})、碘密度图(IDI)与有效原子序数(Z-eff)图的融合图及电子密度图(EDI);记录2种图像中肺段动脉、肺亚段及以下动脉内的栓子数量和位置,对比其中相应肺灌注缺损区与对侧相应正常肺实质区常规CT值、碘密度(ID)、Z-eff及电子密度(ED)的差异;针对差异有统计学意义的sCTPA参数绘制受试者工作特征(ROC)曲线,计算曲线下面积(AUC),评估其区分PE肺灌注缺损区与正常肺实质的效能。结果 37例中,仅以常规CTPA检出37个栓子,其中26个位于肺段动脉、11 个位于肺亚段及以下动脉;之后结合SCTPA后处理图像额外检出1个肺段动脉和2个肺亚段以下动脉内栓子。全部40个栓子对应肺灌注缺损区常规CT值高于、ID及Z-eff均低于对侧正常肺实质区(P均<0.01),而ED与正常肺实质区差异无统计学意义(P=0.54)。以常规CT值区分肺灌注缺损区与正常肺实质区的敏感度、特异度分别为42.50%及87.50%,以ID及Z-eff区分的敏感度分别为95.00%、97.50%,特异度均为100%。ID及Z-eff的AUC均为0.99,均高于常规CT值(0.65,Z=5.56、5.53,P均<0.01),而 ID与Z-eff的AUC差异无统计学意义(Z=0.71,P=0.48)。结论 利用SCTPA可提高PE检出率及定量评估肺组织灌注;根据ID及Z-eff可有效区分肺灌注缺损区与正常肺实质。     

256层螺旋CT肺动脉成像量化评价急性肺动脉栓塞患者右心室功能和肺动脉栓塞程度

目的 应用256层螺旋CT肺动脉成像(CTPA)定量评价急性肺动脉栓塞(APE)患者右心室功能和肺动脉栓塞程度。方法 选择经256层螺旋CTPA证实的APE患者75例, 年龄25~80岁,平均(59.2±13.3)岁,其中男42例,女33例,采用CT肺动脉栓塞分数(obstruction scores,OS)评价APE程度,根据OS值将患者分为轻(n=18,OS<30%)、中(n=25,OS=30%~50%)和重度(n=32,OS<30%),通过测量CT图像上右心室短轴最大直径(RVd)、左心室短轴最大直径(LVd)、右心室短轴与左心室短轴最大直径比率(RVd/LVd)、主肺动脉(MPA)、奇静脉及上腔静脉(SVC)直径评价右心室功能。同时比较3组右心室功能CT参数。结果 CT肺动脉栓塞程度和心血管参数之间有明显相关性(P<0.01),表现为在中、重度APE患者中RVd、RVd/LVd、主肺动脉直径、奇静脉直径及上腔静脉直径均较轻度APE患者高(P<0.05),而LVd值较轻度APE患者低,同时中度和重度APE患者之间这些参数差异也有统计学意义(P<0.05)。结论 应用CTPA得到的量化CT参数对评价APE患者右心室功能和APE程度是十分有力的工具,APE患者右心室功能障碍和APE程度密切相关。     

肺通气?蛐灌注显像与螺旋CT血管成像用于肺栓塞诊断的比较研究

目的:比较通气?蛐灌注(V-P)显像和螺旋CT血管成像(SCTA)对肺栓塞(PE)诊断的临床价值。资料和方法:65例疑有PE的患者同时进行了V-P显像和SCTA检查,包括29例PE和36例非PE患者。以最终临床诊断为标准,分别评价两种显像对PE诊断的临床价值。结果:V-P显像对PE诊断的灵敏度、特异性和准确性分别为86.2%,72.2%和78.5%,SCTA分别为79.3%,91.7%和86.2%。非确定性诊断在V-P显像中占受检病例的16.9%,SCTA占4.6%。V-P显像的非确定性诊断多出现于既往有其它心肺疾患的患者,如将非确定性诊断病例去除,则V-P显像的各项诊断参数均较SCTA呈增高趋势。联合应用两种检查法,则诊断的灵敏度、特异性和准确性分别可提高到93.1%,94.4%和93.8%。结论:总体上SCTA对PE诊断的准确性优于V-P显像,应作为首选检查法;如果对受检病例作适当的选择,V-P显像的诊断价值仍有可能进一步提高;联合应用两种显像是目前最为理想的PE诊断方法。     

The use of D-dimer testing and Wells score in patients with high probability for acute pulmonary embolism

Rationale, aims and objective  To investigate if a combination of Wells pre-test probability score and D-dimer testing could be used as a safe base for making clinical decisions on further investigations for patients with intermediate to high risks of pulmonary embolism (PE).
Methods  One hundred and twenty patients with signs or symptoms of acute PE were investigated with pulmonary angiography (PA) or contrast enhanced computed tomography of the pulmonary arteries (CTPA), D-dimer testing (Tinaquant^®) and clinical scoring using the Wells pre-test probability score during their first 48 hours at the hospital. Patients were recruited consecutively from emergency departments at two teaching hospitals.
Results  The cut-off value of 0.5 mg L⁻¹ in D-dimer analysis is proved adequate with a negative predictive value (NPV) of 92% in this group of patients with intermediate to high risks. The combination of D-dimer testing and Wells score increases the NPV to 94%. The specificities of both tests were low.
Conclusion  D-dimer and Wells pre-test probability scores are safe to rule out acute PE even in patients with at least an intermediate risk of PE, but the specificity is low. D-dimer testing had a higher NPV than Wells score and the combination improved the algorithm further. The cut-off level for a high risk of PE measured with the Wells score was four and it seems reasonable to use that cut-off level in future algorithms. In addition, both PA and CTPA can present false positive and negative results difficult to interpret.     

Contribution of indirect computed tomography venography to computed tomography angiography of the chest for the diagnosis of thromboembolic disease in two United States emergency departments

Summary.  Recent reports suggest that physicians in non-ambulatory settings can use indirect CT venography (CTV) of the lower extremities immediately following spiral CT angiography (CTA) of the chest to identify patients with a negative CTA who have thromboembolic disease identified on CTV. We sought to determine the frequency of isolated deep venous thrombosis (DVT) discovered on CTV in emergency department (ED) patients with complaints suggestive of pulmonary embolism (PE) yet having a negative CTA. This study was conducted in a suburban and urban ED where patients with symptoms suspicious for PE were primarily evaluated with CTA and CTV. A total of 800 patients were studied, including 360 from the suburban ED and 440 from the urban ED. 88 (11%) patients were diagnosed with thromboembolic disease by CTA, or CTV, or both. Seventy-three patients had a CTA of the chest that was positive for PE, 42 (5.2%) of whom had evidence of both PE on CTA and DVT on CTV. Fifteen patients (2%, 95% CI = 1–3%) had a negative CTA and were subsequently found to have isolated DVT on CTV, all of whom received anticoagulation therapy. These data suggest that indirect CT venography of immediately following CT angiography of the chest significantly increased the frequency of diagnosed thromboembolic disease requiring anticoagulation in ED patients with suspected PE.