Ventilation-perfusion (V/Q) lung scintigraphy: a long journey to a renewed position of prominence in diagnosing pulmonary embolism

Clinicians' interpretation of ventilation/perfusion lung scan reports: Where are we today?

Background

Clinicians' interpretation of lung scan reports will determine which further management decisions are taken when potentially fatal pulmonary embolism (PE) is suspected.

Objectives

To assess current referring clinicians' interpretation of the terminology used in ventilation/perfusion (V/Q) scan reports, whether this interpretation is affected by experience level, and how it affects clinical management decisions.

Methods

This was a questionnaire-based cross-sectional study. Between September 2020 and May 2021, 300 questionnaires were distributed among clinicians who refer patients for V/Q scans.

Results

Of the 162 clinicians who responded, 94% thought that there is >85% likelihood of PE or definitely PE present when a scan is reported as 'high probability of PE'; 87% interpreted 'low probability of PE' as <10% likelihood of PE or definitely no PE present. Overall, >70% of clinicians across all experience levels correctly interpreted the intended meaning of probability categories according to the Modified Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II criteria. Of the respondents, 77% agreed that clinically significant PE is ruled out by a normal scan. Further investigation for inconclusive findings, features of parenchymal lung disease and cardiomegaly were selected by 72%, 93% and 98% of clinicians, respectively.

Conclusion

The findings of this study regarding high-probability scan results were in line with existing literature on lung scan report interpretation. However, our findings regarding low-probability scan results and negative V/Q scan specificity contrasted with the findings in these articles, suggesting that clinicians are now more familiar with lung scan interpretation guidelines. Experience level did not significantly affect interpretation of reports. Although most clinicians agreed that a negative scan excludes clinically significant PE, two-thirds of them would still subject the patient to further unnecessary investigations to exclude PE.

Study synopsis

What the study adds. Our findings regarding a low-probability ventilation/perfusion (V/Q) scan and the specificity of a negative V/Q scan contrasted with previous articles on lung scan interpretation, suggesting that clinicians are now more familiar with lung scan interpretation guidelines.Implications of the findings. Although most clinicians understood the negative predictive value of a V/Q scan, 20% would still investigate further with computed tomography pulmonary angiography or treat as confirmed pulmonary embolism. Education of clinicians about the negative predictive value of V/Q scans is important to avoid unnecessary radiation or anticoagulation.

Pulmonary infarction in acute pulmonary embolism

Pulmonary infarction results from occlusion of the distal pulmonary arteries leading to ischemia, hemorrhage and ultimately necrosis of the lung parenchyma. It is most commonly caused by acute pulmonary embolism (PE), with a reported incidence of around 30%. Following an occlusion of the pulmonary artery, the bronchial arteries are recruited as primary source of perfusion of the pulmonary capillaries. The relatively higher blood pressure in the bronchial circulation causes an increase in the capillary blood flow, leading to extravasation of erythrocytes (i.e. alveolar hemorrhage). If this hemorrhage cannot be resorbed, it results in tissue necrosis and infarction. Different definitions of pulmonary infarction are used in literature (clinical, radiological and histological), although the diagnosis is nowadays mostly based on radiological characteristics. Notably, the infarcted area is only replaced by a fibrotic scar over a period of months. Hence and formally, the diagnosis of pulmonary infarction cannot be confirmed upon diagnosis of acute PE. Little is known of the impact and relevance of pulmonary infarction in acute PE, and whether specific management strategies should be applied to prevent and/or treat complications such as pain, pneumonia or post-PE syndrome. In this review we will summarize current knowledge on the pathophysiology, epidemiology, diagnosis and prognosis of pulmonary infarction in the setting of acute PE. We highlight the need for dedicated studies to overcome the current knowledge gaps.

Applying Wells score to inconclusive perfusion only modified PIOPED II (Prospective Investigation of Pulmonary Embolism Diagnosis II) readings in order to optimize the lung scintigraphy diagnostic yield in acute pulmonary embolism detection

OBJECTIVE

When using perfusion only modified PIOPED II criteria for PE detection, generated non-diagnostic scans are found to be the main diagnostic restriction. The objective of current study is to identify the role of Wells criteria added to inconclusive readings with the intent of enhancing the lung scintigraphy diagnostic yield.

METHODS

CTPA was performed in 34 suspected PE patients with inconclusive lung scintigraphy. They also were evaluated by Wells score and classified as low, intermediate and high probability. Overall prevalence and the rate of PE for each probability were calculated. Furthermore, NPV for scores < 2 and PPV for scores > 6 were computed.

RESULTS

Having a mean age of 59.75 ± 17.38 years, 7 (20.6%), 23 (67.6%) and 4 (11.8%) of cases had total criteria point count < 2, 2-6 and > 6, respectively. Using CTPA, 5 patients (14.7%) were diagnosed with PE. None of the patients with scores < 2 had PE with an associated NVP of 100%. Patients with scores 2-6 had a PE rate of 4.3% and 100% of patients with scores > 6 were diagnosed with PE, implying that the PPV of scores > 6 was 100%.

CONCLUSION

Adding Wells score to non-diagnostic scans allowed identification of PE to be done reliably, and provided further insight into how lung scintigraphy in conjunction with clinical assessment is a practical strategy not only for the patients unfit for performing CTPA but also in all the patients referred for PE evaluation.

A Brief History of Lung Ventilation and Perfusion Imaging Over the 50-Year Tenure of the Editors of Seminars in Nuclear Medicine

The ventilation/perfusion lung scan has been in continuous use for approximately half a century, the same lifetime as Seminars in Nuclear Medicine. Remarkably, the founding Editors-in-Chief have continued to guide the journal over this entire period. In this Feschrift issue celebrating their enormous contribution, we review the history of the lung scan, its highs and lows, the transition from planar to SPECT/CT V/Q scans, and the future that is in store in this age of multimodality functional imaging. We concur with the published view of one of the retiring editors (LMF) that V/Q scintigraphy is indeed alive and well and has a definite future in clinical medicine.