Vanishing tumour | Radiology Signs

Answer:

A vanishing tumour, or phantom tumour, is a well-defined, homogeneous, elliptical or lenticular opacity produced by pleural fluid loculated within an interlobar fissure, which mimics a pulmonary mass. It is classically seen in decompensated heart failure, where raised hydrostatic pressure drives transudate into the fissure, and it is favoured by pre-existing pleural adhesions that prevent the fluid dispersing. The minor (horizontal) fissure on the right is the commonest site, followed by the major fissures; involvement may be bilateral. The diagnostic hallmark is complete resolution, sometimes within days, once the heart failure is treated with diuresis, which is what gives the lesion its name. Its fissural location and lens shape on the lateral film usually suggest the diagnosis, and CT confirms fluid attenuation with tapering margins along the fissure; ultrasound can also demonstrate the collection. The differential includes a genuine pulmonary nodule or mass, a pleural fibrous tumour, empyema, haemothorax and asbestos-related pleural disease.

Why is it called so?

The opacity looks like a tumour but vanishes when the underlying heart failure is treated.

Pathophysiology

In cardiac failure, elevated pulmonary capillary and systemic venous pressures increase transudation into the pleural space beyond the capacity of lymphatic reabsorption. Where visceral pleural surfaces are adherent from previous inflammation, the fluid entering the interlobar fissure cannot spread freely and is trapped as a discrete loculus. Confined between two pleural leaves, it assumes a biconvex lenticular shape with tapering ends that follow the plane of the fissure, and on the frontal projection, viewed obliquely, the well-defined margins of that lens simulate a solid mass. Restoring the pressure balance with diuresis allows reabsorption and the collection disappears.

Alternative names: Phantom tumour, pseudotumour of the lung, disappearing tumour

Other associated named signs: Incomplete border sign, comet tail sign of rounded atelectasis, and the meniscus sign of free pleural fluid

References

1. Mohamed MM, Iyow SN, Ahmed MS, Abdilahi JF, Ahmed AA, Hökenek NM. Fissural pleural effusion mimicking a lung mass: a diagnostic pitfall in the Emergency Department. Int J Emerg Med. 2026;19(1). PMID: 42032466.