CHEST IMAGING : CH 12. Transverse CT scan obtained in a 60-year-old man with Bronchioloalveolar carcinoma: Multiple nodules surrounded by a halo.

THE CT HALO SIGN

H.FOURATI, W.FEKI, E.DAOUD, H.ABID*, S.HADDAR*, M.A.KAMOUN, Z.MNIF AYADI Radiology service, Hedi Chaker 's Hospital*Radiology service, Habib Bourguiba Hospital

CHEST IMAGING : CH 12

INTRDODUCTION

The Computed Tomographic (CT) Halo Sign refers to a zone of ground-glass attenuation surrounding a pulmonary nodule or mass on CT images.

OBJECTIVES

Our purpose is to show different pathological conditions related to this sign.

MATERIALS AND METHODS

A retrospective study about 18 patients.

The average age ranged from 15 to 60 years old.

All of our patients underwent a chest CT with thin reconstructions.

RESULTS

The diagnosis was:

Invasive pulmonary aspergillosis (12 cases) Lymphoma (2 cases) Bronchioloalveolar carcinoma (1 case) Pulmonary candidiasis (1 case) Wegener granulomatosis (1 case) Bronchiolitis Obliterans Organizing Pneumonia ( BOOP) (1case)

RESULTSCASE N°1:

Transverse CT scan obtained in a 60-year-old man with Bronchioloalveolar carcinoma: Multiple nodules surrounded by a halo of ground glass opacity.

RESULTSCASE N°2:

Pulmonary lymphoma in a 35-year-old man with a history of acute respiratory failure.Theses sections CT shows multiple masses and nodules with a surrounding halo of ground glass opacity in both lungs.

RESULTSCASE N°3:

A girl, 16 years-old , LAM4, 2 parenchymal nodules surrounded by ground-glass attenuation.Aspergillus antigenemia was positive.The diagnosis retained : Invasive pulmonary aspergillosis.

RESULTSCASE N°4:

15 years-old , LAM4, febrile neutropenia, dry coughA- Thin sagittal reconstruction: The Air crescent signB - coronal reconstruction: The CT halo signInvasive pulmonary aspergillosis

RESULTSCASE N°5:

23 years-old, Hodgkin lymphoma, control after 4 cures of chemotherapy. Multiple parenchymal nodules surrounded by ground-glass attenuation. Pulmonary Candidiasis

RESULTSCASE N°6:

BOOP in a 48-year-old man who consults for hemoptysis when he stopped steroids . These sections CT demonstrates multiple masses with the CT halo sign in the right lung field.

DISCUSSION

Although it was initially proposed as an early, specific finding of invasive pulmonary aspergillosis, the CT halo sign can be caused by many other pathological conditions (infection, neoplastic and inflammatory diseases).

Thus, the sign itself is non-specific. However, in the appropriate clinical setting, the sign may be very helpful +++

DISCUSSION EXPLANATION

The presence of a halo of ground-glass attenuation is usually associated with hemorrhagic nodules .

This CT appearance was described by Kuhlman et al in patients with invasive aspergillosis.

In severely neutropenic patients, the CT halo sign is highly suggestive of infection by an angioinvasive fungus, most commonly Aspergillus. Vascular invasion by this fungus results in thrombosis of small- to medium-sized vessels, which causes ischemic necrosis .

DISCUSSION EXPLANATION

At pathologic examination:the nodules represent foci of infarctionthe halo of ground-glass attenuation results from alveolar hemorrhage .

Although it is less common, the halo sign may also be observed in nonhemorrhagic nodules, in which case either tumor cells or inflammatory infiltrate account for the halo of ground-glass attenuation.

DISCUSSION

INFECTIOUS DISEASES

DISCUSSIONInfectious diseases

Early recognition of pulmonary or systemic fungal infection is critical because this disease is associated with a high mortality rate (50% 90%) .The frequency of the halo sign in patients with invasive aspergillosis is relatively high in the early stages of the disease, but alters with time and becomes progressively less frequent. The air crescent sign ,which has also been associated with invasive aspergillosis, may be found later in the course of the disease, when the patient is recovering from neutropenia.

Kami et al showed that chest CT is more sensitive in the diagnosis of early invasive aspergillosis than is currently available serologic testing used to detect circulating Aspergillus antigens.

DISCUSSIONInfectious diseases

Other angioinvasive fungal species: Mucormycosis (opportunistic infection usually seen in immunocompromised patients or patients

with diabetes mellitus or renal disease)

Pulmonary Candidiasis (disseminated miliary nodules, each less than 1 cm in diameter, which is usually distinct from invasive pulmonary aspergillosis)

Coccidioidomycosis.

DISCUSSIONInfectious diseases

Other infectious diseases:

Cryptococcosis (cryptococcosis may display solitary or multiple pulmonary nodules with or without the CT halo sign, particularly in immunocompromised patients)

Cytomegalovirus

Herpes Simplex Virus

• Major causes of pulmonary morbidity and mortality in the immunocompromised host. •These viruses may cause interstitial pneumonia, haemorrhagic nodules, and diffuse alveolar damage, and predominantly show areas of ground glass attenuation and/or focal areas of consolidation. •Nodules with the CT halo sign are rarely present.

DISCUSSIONInfectious diseases

Some infectious diseases have been reported to show the halo

sign of uncertain pathological causes:

Mycobacterium avium complexCoxiella burnettiMyxovirus Septic embolismTuberculosis (The cause of the halo sign in patients with a pulmonary tuberculoma was presumed inflammation or perilesional haemorrhage due to rupture of an arterial vessel )

DISCUSSION

NEOPLASTIC DISEASES

DISCUSSIONNeoplastic diseases

Lung metastases from hypervascular tumors : angiosarcoma, choriocarcinoma, osteosarcoma and melanoma (perilesional hemorrhage secondary to the fragility of neovascular tissue).

Pulmonary Kaposi sarcoma (typically manifests as ill-defined nodules predominantly seen in a peribronchovascular distribution. The disease may also show haemorrhagic nodules with the halo sign ).

Bronchioloalveolar carcinoma commonly appears as a solitary peripheral nodule associated with ground glass attenuation was reported to be the most common condition showing the CT halo sign in immunocompetent patients

may also show pseudocavitation In the presence of this sign, the CT halo sign is characteristic enough to suggest bronchioloalveolar carcinoma .

DISCUSSIONNeoplastic diseases

Pulmonary lymphoproliferative disorders ( lymphoma or post-transplantation lymphoproliferative disorders): solitary or multiple pulmonary nodules are the most common radiographic findings. The lesion is often associated with a surrounding halo of ground glass opacity

Metastatic pulmonary neoplasms

Lung metastases from extrapulmonary adenocarcinoma

DISCUSSION

NON-NEOPLASTICNON-INFECTIOUS

DISEASES

DISCUSSIONNon-neoplastic non-infectious diseases

Wegener's granulomatosis Pulmonary endometriosis with catamenial haemorrhage Hydatidiform mole

Eosinophilic lung diseases parasitic infestation such as schistosomiasis, simple pulmonary eosinophilia (Loeffler

syndrome) , or idiopathic hypereosinophilic syndrome Bronchiolitis Obliterans Organizing Pneumonia ( BOOP) Iatrogenic injuries :Pulmonary artery catheterization

Transbronchial biopsy • Lung transplants

DISCUSSIONThe radiologists should be familiar with THE CT HALO SIGN because clinical settings and associated radiological features help to narrow the differential diagnosis.

In immunocompromised patients: Multiple nodules + The CT halo sign =~ suggest infectious diseases Kaposi's sarcomalymphoproliferative pulmonary disorders “Particularly in patients with acute leukaemia and bone marrow transplant recipients with fever, the presence of the CT halo sign strongly suggests invasive pulmonary aspergillosis”.

DISCUSSIONIn a study by Jasmer et al:Nodules < 1 cm, especially those with a centrilobular distribution, suggested an infectious etiology. A peribronchovascular distribution was suggestive of KS.

In immunocompetent patients: A solitary nodule + the CT halo sign + pseudocavitation bronchioloalveolar.

DISCUSSION

Table .: List of diseases showing the CT halo sign

CONCLUSION•The CT halo sign may be seen with a wide spectrum of pulmonary diseases.

•It is most commonly associated with hemorrhagic nodules and is more rarely associated with tumor cell or inflammatory infiltrate.

•Notwithstanding this wide spectrum of associated diseases, the CT halo sign is a useful diagnostic clue in the appropriate clinical setting and may be the first evidence of pulmonary fungal infection.