A common subtype of perceptive radiologic error is the so-called "edge-of-film" finding, which has persisted long enough to generate a category of its own. Abnormalities at the edges of the film are more likely to be missed than those at the center. The brain and skull base are at the superior edge of cervical spine films, while the great neck vessels and airway course along the anterior margin (Figure 12). In the lumbar spine, the conus medullaris appears at the superior edge, with the sacrum appearing inferiorly and the lower gastrointestinal tract or genitourinary structures appearing anteriorly.
Elderly patient with neck pain. Sagittal T1 image (A) shows abnormal marrow signal in the clivus (arrow). The patient was otherwise asymptomatic. Subsequent CT (B) confirmed a large lytic lesion in the clivus (arrow). Upon further questioning, patient reported a history of a pituitary tumor resection and radiation therapy. Post-treatment changes were favored with imaging surveillance recommended.
While not extraspinal, abnormal signal intensity in the conus medullaris sometimes goes undetected on lumbar spine studies, resulting in callbacks for additional contrast imaging of the cervical and thoracic spine (Figures 13–15). Other subtle findings may include prominent vessels in cases of dural arteriovenous fistulae (Figure 13). The most common important sacral abnormalities that may be missed are nondisplaced fractures (Figure 16), which can be subtle in older and osteopenic patients.
Lower thoracic canal stenosis. Sagittal T2 of the lumbar spine in an elderly patient with an edge-of-film severe lower thoracic canal stenosis (arrow).
Adolescent with low back pain and bilateral L4 pars interarticularis defects on lumbar MRI. Sagittal T2 image (A) shows abnormal signal in the conus medullaris just at the edge of the image (arrow). Subsequent thoracic spine MRI (B) recommended by the interpreting neuroradiologist shows an extensive syrinx in the thoracic spinal cord (arrow). Brain MRI (C) shows an asymptomatic Chiari I deformity (arrow). Images courtesy of Adam Blanchard, MD, American Radiology Associates, Dallas, Texas.
Middle-aged patient with low back pain and progressive weakness. Sagittal STIR (A) lumbar MRI shows abnormal signal in the conus medullaris (arrow). Based on this finding, a thoracic MRI (B) shows abnormal T2 signal (arrow) in the thoracic spinal cord and subtle abnormal vascularity along the dorsal surface of the cord. These findings were suspicious for a spinal vascular malformation. Spinal angiography (C) confirmed a spinal dural arteriovenous fistula (arrow). Thoracic spine MRI (D) several months after embolization showed substantial interval improvement in spinal cord edema (arrow) and abnormal vascularity.
Older patient with persistent back pain after lumbar surgery. Axial T1 image (A) shows abnormally low T1 marrow signal through the sacral alae, suspicious for bilateral sacral insufficiency fractures (arrows). Fractures are confirmed on follow-up noncontrast CT of the pelvis (B).
Appl Radiol. 2022;51(2):15-23. © 2022 Anderson Publishing, Ltd.