Radiology

Red flags include suspected epidural abscess or hematoma presenting with acute pain, but no neurological symptoms (urgent imaging is required); suspected cancer; suspected infection; cauda equina syndrome; severe or progressive neurologic deficit; and suspected compression fracture. In patients with suspected uncomplicated herniated disc or spinal stenosis, imaging is only indicated after at least a six-week trial of conservative management and if symptoms are severe enough that surgery is being considered.

Red flags include Glasgow Coma Scale (GCS) less than 13; GCS less than 15 at 2 hours post-injury; a patient aged 65 years or older; obvious open skull fracture; suspected open or depressed skull fracture; any sign of basilar skull fracture (e.g., hemotympanum, raccoon eyes, Battle’s Sign, CSF otorhinorrhea); retrograde amnesia to the event lasting 30 minutes or longer after the event; “dangerous” mechanism (e.g., pedestrian struck by motor vehicle, occupant ejected from motor vehicle, or fall from higher than 3 feet or down more than 5 stairs); and coumadin-use or bleeding disorder.

Red flags include recent onset, rapidly increasing frequency and severity of headache; headache causing the patient to wake from sleep; associated dizziness, lack of coordination, tingling or numbness, new neurologic deficit; and new onset of a headache in a patient with a history of cancer or immunodeficiency.

Although CT is accurate in the evaluation of suspected appendicitis in the pediatric population, ultrasound is nearly as good in experienced hands. Since ultrasound will reduce radiation exposure, ultrasound is the preferred initial imaging examination in children. If the results of the ultrasound exam are equivocal, it may be followed by CT. This approach is cost-effective, reduces potential radiation risks and has excellent accuracy, with reported sensitivity and specificity of 94 percent.

X-rays are only indicated if there is pain in the malleolar zone, bone tenderness at the posterior edge or tip of either malleolus, or inability to bear weight for four steps immediately after the trauma and in the emergency department.

In adults with shoulder pain, if further investigation is required after the initial X-ray assessment, ultrasound is recommended as the next imaging modality for the evaluation of soft tissue pathology (such as rotator cuff tear, tendinopathy, effusion, bursitis, soft tissue calcification, or extra-articular impingement).

If x-ray demonstrates imaging findings that may predispose to femoroacetabular impingement (FAI), then consultation to a musculoskeletal specialist is suggested as MRI may neither be required nor advance diagnosis or management.

For patients with hip or knee pain likely related to degenerative joint pathology, if x-ray demonstrates greater than mild osteoarthritis, MRI may not be indicated as it often will not advance diagnosis or management. Musculoskeletal specialist consultation should be considered, to determine if MRI is required.

Not all pulmonary nodules require imaging surveillance. Benign nodules are common and often represent sequelae of a prior healed infectious or inflammatory process, benign endobronchial mucus plugs or pulmonary lymph nodes. Specifically, nodules with a benign pattern of calcification do not require any CT or chest radiograph surveillance and should be clearly described as benign in the radiology report. These include nodules that are completely calcified, small nodules with central calcification and nodules with a complete circumferential ring of calcification. Calcification may be difficult to identify without thin section (less than 2 mm) slice reformats. Incidental nodules meeting criteria for a perifissural nodule typical for an intrapulmonary lymph node do not require surveillance. Perifissural lymph nodes have a characteristic CT appearance: located along a fissure, smoothly marginated, homogenously solid, polygonal, triangular or ovoid shaped and measuring less than 10mm. Regardless of CT or chest radiograph appearance an incidental solid nodule that has been stable for 2 years can also be safely considered benign (note that many nodules only require one year of surveillance). By making it clear that a nodule does not meet criteria for surveillance, radiologists may reduce unnecessary imaging. Radiologists may wish to describe some benign nodules as post inflammatory, rather than “non-specific” to help reduce anxiety and limit over investigation. Referencing relevant practice guidelines can provide added confidence and can add support to the radiologist’s recommendation.

Joint recommendation with the Canadian Thoracic Society

Incidental pulmonary nodules are commonly detected on chest CT, and extensive evidence demonstrates that the majority of solid nodules have a low probability of malignancy. Multiple validated clinical and Bayesian prediction models confirm that malignancy risk varies widely based on nodule characteristics and patient factors, making uniform follow-up inappropriate and potentially harmful. When radiology reports identify incidental nodules without providing explicit follow-up recommendations, including clear statements when no surveillance is indicated, clinical management becomes variable, leading to unnecessary repeat imaging, increased healthcare costs, cumulative radiation exposure, and patient anxiety. This variability is further amplified by known inter-observer differences in nodule detection and classification, underscoring the importance of standardized guidance within reports to ensure consistent downstream care. International guidelines from the Fleischner Society and British Thoracic Society, as well as recent Canadian expert consensus recommendations, emphasize risk-stratified management and clearly define scenarios in which routine follow-up is not required. Including clear, guideline-based follow-up recommendations within CT reports, particularly explicit statements indicating when no further imaging is necessary, improves communication between radiologists and referring clinicians, reduces practice variability, supports appropriate risk-based decision-making, and minimizes low-value imaging while ensuring timely and appropriate surveillance for nodules with clinically meaningful malignancy risk.

Current evidence regarding malignant risk of pulmonary nodules by size is based on either 2-dimensional mean measurements or volume measurements. Mean dimension can be calculated by the average of the longest dimension and the perpendicular short axis dimension on a single CT plane. This is best measured in whichever plane produces the largest mean dimension value. Measurements should be made with thin section reconstruction (maximum thickness 1.5 mm). If radiologists report only the longest diameter, malignant risk will be overestimated, particularly for irregular (non-spherical) nodules. Using longest dimension to guide recommendations may result in unnecessary surveillance, over surveillance and over investigation. Guidelines from the Fleischner society regarding incidental pulmonary nodules use mean, not longest, dimension. ACR LungRADS® guidelines regarding management of screen-detected nodules also use mean dimension.

Joint recommendation with the Canadian Thoracic Society

Accurate assessment of pulmonary nodule growth requires reviewing all available prior imaging, and not just the most recent prior scan. Guideline frameworks emphasize longitudinal comparison over an extended interval often up to two years for solid nodules, 5 years for subsolid nodules, because stability over a longer period of time favours benignity. Volume doubling times for solid cancers are in the range of 100-400 days whereas mean doubling times for subsolid nodules are 3-5 years. The Fleischner Society’s 2017 Guidelines underscores serial assessment to accurately determine if a nodule is increasing in size. This is of critical importance for subsolid nodules that are typically indolent and slow-growing. For subsolid nodules, it is often necessary to compare to the oldest prior CT scan or baseline CT scan that is available to appreciate the slow growth in size and/or density. Restricting comparison to only the most recent CT scan increases the risk of misclassifying a nodule as stable when in fact it is slowly increasing in size when compared to remote CT scans or the baseline CT scan.

Joint recommendation with the Canadian Thoracic Society