# The reverse halo sign in emergency chest CT: A diagnostic guide across diverse pulmonary conditions

## TL;DR

This paper explains how a specific CT scan pattern called the reverse halo sign helps doctors diagnose various lung conditions quickly.

## Contribution

It provides a diagnostic guide for recognizing and interpreting the reverse halo sign in emergency chest CT scans across diverse pulmonary conditions.

## Key findings

- The reverse halo sign is observed in organizing pneumonia and other pathologies.
- It aids in differential diagnosis and patient management in emergency settings.
- The sign appears in infectious, inflammatory, vascular, malignant, and traumatic conditions.

## Abstract

The atoll sign, also known as the reverse halo sign (RHS), is defined by a central ground-glass opacity encircled by a rim of consolidation. Originally described in the context of organizing pneumonia, it is now recognized across a spectrum of conditions—including infectious, inflammatory, vascular, malignant, and traumatic pathologies. This pictorial essay examines the various clinical scenarios in which the RHS is observed on emergency CT, highlighting its crucial role in differential diagnosis and patient management.

The online version contains supplementary material available at 10.1007/s10140-025-02337-2.