Cosmic Signs in Radiology: A Pictorial Review

Abstract

Pattern recognition remains a cornerstone of radiologic interpretation, as it facilitates a confident and comprehensive differential diagnosis. Certain pathologies present with specific and highly recognizable patterns on imaging modalities. These patterns can resemble familiar real-life phenomena, including cosmic bodies that surround us. We present in this article a compilation of radiologic signs across various modalities that take inspiration from cosmic phenomena. For each sign, we summarize its defining imaging appearance, typical clinical context, and common pitfalls; where available, we note diagnostic performance (e.g., sensitivity/specificity) to guide appropriate weighting in practice. By coupling memorable imagery with succinct clinical guidance, this pictorial review aims to support a faster, more accurate pattern recognition that is applicable in both low-resource and tertiary care settings, while recognizing that these signs function as educational aids rather than validated diagnostic tests. In familiarizing themselves with these classic signs, training radiologists can benefit from an engaging and memorable way of recognizing various pathological conditions.

Keywords: cosmic signs; pattern recognition; radiographic image interpretation; radiologic diagnosis; radiological signs; radiology interpretation.

Figure 1

Small calcific/crystalline highly reflective structure causing reverberation artifact on ultrasound of the thyroid (yellow arrows) (b), axial CT of the chest showing a curvilinear opacity extending from a subpleural mass toward the ipsilateral hilum with distortion of vessels and bronchi (red arrow) (c), and tail of soft tissue extending from a calcification, representing the collapsed/scarred/thrombosed parent vein on a non-enhanced CT of the pelvis (green arrow) (d), all resembling a comet tail (a).

Figure 2

The Earth as it appears from outer space (a), with resemblance to the flattening and posterior displacement of the heart by the tension pneumomediastinum on a plain chest radiograph (b). Figure used with permission of the author G. A. O. Carillo; The Lancet, 2014 [19].

Figure 3

An image depicting a far galaxy (a) with resemblance to the CT view of the chest showing mass-like regions composed of numerous smaller granulomas with a central core and peripheral nodules seen in sarcoidosis (red arrows) (b).

Figure 4

Plain radiograph of the shoulder showing lateral displacement of the humeral head with respect to the glenoid, losing the half-moon overlap (black arrow) (a), compared to a plain radiograph of a normal shoulder, illustrating the half-moon overlap (b).

Figure 5

A rendering of the Milky Way galaxy as it appears from space (a), resembling the junction between the fibroglandular tissue and the retromammary fat, with an appearance analogous to that of a dark galaxy studded with stars seen on mediolateral oblique (MLO) (b) and craniocaudal (CC) (c) views of the left breast (yellow arrows). The galaxy also resembles the multiple punctate regions of high T2 surrounding the main component of the lesion in PML (red arrows) (d,e).

Figure 6

The appearance of a starfield pattern in space (a), which holds resemblance to the multiple bright foci on MR diffusion weighted images on axial cuts of the brain (red arrows) (b).

Figure 7

Coronal CT images of the abdomen and pelvis showing a conglomerate of inflamed bowel loops interconnected by multiple fistulous tracts (b,c), giving a star-shaped configuration (yellow arrows) resembling its natural counterpart (a).

Figure 8

The appearance of a starry sky (a), resembling bright echogenic dots throughout a background of decreased liver parenchymal echogenicity on ultrasound (green arrows) (b), and small innumerable T2 hyperintense bile duct hamartomas and biliary microhamartomas, scattered throughout the T2 hypointense hepatic parenchyma (red arrows) (c).

Figure 9

A sunburst appearance observed in nature (a), which resembles the aggressive periosteal reaction with stretching of Sharpey’s fibers perpendicular to the humeral bone on plain radiograph (red arrows) (b), the spoke wheel pattern of vessels in meningioma viewed in cross-section, diverging from dural attachment on brain MRI (green arrows) (c), sagittal T2 images of the brain showing radial orientation of the sulci from the roof of the third ventricle due to dysgenesis of the cingulate gyrus and corpus callosum (green arrows) (d), and the appearance of arterial blush seen at selective arterial DSA of a renal angiomyolipoma (blue arrows) (e).

Figure 10

Alternating colors on Doppler signal behind a reflective object (such as a calculus) (yellow arrows) (b), giving the appearance of turbulent blood flow and resembling a twinkling sky (a).

Figure 11

The appearance of a waxing gibbous, soon to be a crescent moon (a) resembling a linear cleft due to subchondral fracture in the setting of osteonecrosis seen on plain shoulder radiograph (yellow arrows) (b).

Figure 12

Unenhanced chest CT with findings of the hyperdense crescent sign noted along the left lateral wall of a saccular aneurysm arising from the distal aortic arch (white arrow).

Figure 13

Compression and lateral displacement of the inguinal canal contents by the hernia to form a semicircle of tissue seen lateral to the hernia on axial CT images of the pelvis (yellow arrows) (b), resembling a crescent moon (a).

Figure 14

Axial CT of the chest showing a nodular opacity with retracted infarcted lung and crescentic and circular cavitation in pulmonary aspergillosis (red arrows).

Figure 15

The appearance of a halo surrounding the sun (a), resembling a ground glass opacity surrounding a pulmonary nodule, which represents hemorrhage in a case of early pulmonary aspergillosis on axial CT images of the chest (red arrows) (b).

Figure 16

Fat halo sign in longstanding ulcerative colitis. Infiltration of the submucosa with fat between the muscularis propria and the mucosa at the level of the sigmoid colon on axial CT images of the pelvis (red arrows).

Figure 17

Axial images of the chest showing central ground-glass opacity surrounded by denser air-space consolidation in the shape of a crescent or a ring in organizing pneumonia (red arrow and circle).