Search tips
Search criteria 


Logo of thijTexas Heart Institute JournalSee also Cardiovascular Diseases Journal in PMCSubscribeSubmissionsTHI Journal Website
Tex Heart Inst J. 2009; 36(3): 264–265.
PMCID: PMC2696502

The Air Crescent Sign

Causes and Characteristics
Raymond F. Stainback, MD, Section Editor
Department of Adult Cardiology, Texas Heart Institute at St. Luke's Episcopal Hospital, 6624 Fannin Street, Suite 2480, Houston, TX 77030

A 41-year-old man who was undergoing chronic hemodialysis for end-stage renal disease presented with new-onset hemoptysis. His chest radiograph showed an opacified middle lobe (Fig. 1), a change from earlier radiographs. Two weeks later, the middle lobe contained a large cavity with a nonmobile, intracavitary, rounded mass (Fig. 2). Core biopsy of the cavitary lesion disclosed necrotic tissue with intravascular fungal elements (Fig. 3); culture grew Aspergillus fumigatus.

figure 20FF1
Fig. 1 Chest radiograph shows cardiomegaly with bilateral alveolar infiltrates and opacification of the middle lobe.
figure 20FF2
Fig. 2 Chest radiograph shows a large cavity in the middle lobe with an intracavitary fungus ball (arrows).
figure 20FF3
Fig. 3 Photomicrograph shows necrotic tissue with fungal elements (arrows) in the wall and lumen of a blood vessel (H & E, orig. ×200).


The air crescent sign (ACS), also called the meniscus or cap sign,1 appears on radiographs or computed tomographic scans of the chest as air interposed between an intracavitary, ball-like mass and the cavity wall. Its shape ranges from crescent-like to that of total encapsulation,2 and its volume varies greatly.

By far the most common cause of the ACS is the fungus ball of angioinvasive aspergillosis.1,2 Formed of condensed hyphae, the ball can be large or small, solitary or multiple.1,2 It may move when the patient's position changes3,4 or remain fixed, projecting into the cavity's lumen like a polyp.1 Occasionally, the ball partially calcifies,1,5 or it may disintegrate and exit as particles in the sputum.1 Although often indolent with few or no symptoms,5 the process frequently presents with hemoptysis, which can sometimes be fatal.3

Additional causes of the ACS include pulmonary hydatid cyst,1,6 other fungi,1,2,5 blood clot or Rasmussen aneurysm in a tuberculous cavity,1 lung abscess with inspissated pus,1 staphylococcal pneumonia,6 nocardial infection,1,2 carcinoma of the lung,4 and pulmonary gangrene or hematoma.1


Address for reprints: Herbert L. Fred, MD, MACP, 8181 Fannin St., Suite 316, Houston, TX 77054


1. Felson B. Chest roentgenology. Philadelphia: WB Saunders Co.; 1973. p. 319, 327–9.
2. Abramson S. The air crescent sign. Radiology 2001;218(1): 230–2. [PubMed]
3. Karas A, Hankins JR, Attar S, Miller JE, McLaughlin JS. Pulmonary aspergillosis: an analysis of 41 patients. Ann Thorac Surg 1976;22(1):1–7. [PubMed]
4. Wang LF, Chu H, Chen YM, Perng RP. Adenocarcinoma of the lung presenting as a mycetoma with an air crescent sign. Chest 2007;131(4):1239–42. [PubMed]
5. Levin EJ. Pulmonary intracavitary fungus ball. Radiology 1956;66(1):9–16. [PubMed]
6. Gold W, Vellend H, Brunton J. The air crescent sign caused by Staphylococcus aureus lung infection in a neutropenic patient with leukemia. Ann Intern Med 1992;116(11):910–1. [PubMed]

Articles from Texas Heart Institute Journal are provided here courtesy of Texas Heart Institute