THE CT HALO SIGN

1. CHEST IMAGING : CH 12 THE CT HALO SIGN H.FOURATI, W.FEKI, E.DAOUD, H.ABID*, S.HADDAR*, M.A.KAMOUN, Z.MNIF AYADI Radiology service, HediChaker 's Hospital *Radiology service, HabibBourguiba Hospital

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

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

4. 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.

5. RESULTS The diagnosis was: Invasive pulmonary aspergillosis (12 cases) Lymphoma (2 cases)  Bronchioloalveolar carcinoma  (1 case)   Pulmonary candidiasis  (1 case) Wegener granulomatosis (1 case) BronchiolitisObliterans Organizing Pneumonia ( BOOP) (1case)

6. RESULTS CASE N°1: Transverse CT scan obtained in a 60-year-old man withBronchioloalveolarcarcinoma: Multiple nodules surrounded by a halo of ground glass opacity.

7. RESULTS CASE N°2: Pulmonarylymphomain a 35-year-old man with a history of acute respiratoryfailure. Theses sections CT shows multiple masses and nodules with a surrounding halo of ground glass opacity in both lungs.

8. RESULTS CASE N°3: A girl, 16 years-old , LAM4, 2 parenchymal nodules surrounded by ground-glass attenuation. Aspergillus antigenemiawas positive. The diagnosisretained :Invasive pulmonary aspergillosis.

9. RESULTS CASE N°4: 15 years-old , LAM4, febrile neutropenia, dry cough A- Thin sagittal reconstruction: The Air crescent signB - coronal reconstruction: The CT halo sign Invasive pulmonary aspergillosis

10. RESULTS CASE N°5: 23 years-old, Hodgkin lymphoma, control after 4 cures of chemotherapy. Multiple parenchymal nodules surrounded by ground-glass attenuation. Pulmonary Candidiasis

11. RESULTS CASE 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 lungfield.

12. DISCUSSION Although it was initially proposedas 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 +++

13. 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 .

14. DISCUSSION EXPLANATION At pathologic examination: the nodules represent foci of infarction the 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.

15. DISCUSSION INFECTIOUS DISEASES

16. DISCUSSION Infectiousdiseases 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.

17. DISCUSSION Infectiousdiseases Other angioinvasive fungal species: Mucormycosis(opportunisticinfection usually seen in immunocompromised patients or patientswith 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.

18. DISCUSSION Infectiousdiseases Other infectious diseases: Cryptococcosis(cryptococcosis may display solitary or multiplepulmonary nodules with or without the CT halo sign, particularlyin immunocompromised patients) Cytomegalovirus Herpes Simplex Virus • Major causes of pulmonary morbidity and mortality in theimmunocompromised host. • These viruses may cause interstitialpneumonia, haemorrhagic nodules, and diffuse alveolar damage,and predominantly show areas of ground glass attenuation and/orfocal areas of consolidation. • Nodules with the CT halo signare rarelypresent.

19. DISCUSSION Infectiousdiseases Some infectious diseases have been reported to show the halosign of uncertain pathological causes: Mycobacteriumavium complex Coxiellaburnetti Myxovirus Septic embolism Tuberculosis (The cause of the halo sign in patients with a pulmonarytuberculoma was presumed inflammation or perilesionalhaemorrhagedue to rupture of an arterial vessel )

20. DISCUSSION NEOPLASTIC DISEASES

21. DISCUSSION Neoplasticdiseases Lung metastases from hypervascular tumors : angiosarcoma, choriocarcinoma, osteosarcoma and melanoma (perilesional hemorrhage secondary to the fragility of neovascular tissue). Pulmonary Kaposi sarcoma (typically manifestsas ill-defined nodules predominantly seen in a peribronchovasculardistribution. The disease may also show haemorrhagic noduleswith the halo sign ). Bronchioloalveolarcarcinoma commonly appears as a solitary peripheral nodule associatedwith ground glass attenuation was reported to be the most commoncondition showing the CT halo sign in immunocompetent patients may also show pseudocavitationIn the presence of this sign, the CT halo sign is characteristic enoughto suggest bronchioloalveolar carcinoma .

22. DISCUSSION Neoplasticdiseases Pulmonary lymphoproliferative disorders ( lymphomaor post-transplantation lymphoproliferative disorders): solitaryor multiple pulmonary nodules are the most common radiographicfindings. The lesion is often associated with a surroundinghalo of ground glass opacity Metastatic pulmonary neoplasms Lung metastases from extrapulmonaryadenocarcinoma

23. DISCUSSION NON-NEOPLASTIC NON-INFECTIOUS DISEASES

24. DISCUSSION Non-neoplastic non-infectiousdiseases Wegener's granulomatosis Pulmonaryendometriosis with catamenialhaemorrhage Hydatidiform mole Eosinophilic lung diseases parasitic infestation suchas schistosomiasis, simple pulmonary eosinophilia (Loefflersyndrome) , or idiopathic hypereosinophilic syndrome BronchiolitisObliterans Organizing Pneumonia ( BOOP) Iatrogenic injuries :Pulmonary artery catheterizationTransbronchial biopsy Lung transplants

25. DISCUSSION The radiologistsshould be familiar with THE CT HALO SIGN because clinical settingsand associated radiological features help to narrow the differentialdiagnosis. In immunocompromised patients: Multiple nodules + The CT halo sign =~suggest infectious diseases Kaposi's sarcoma lymphoproliferativepulmonary disorders “Particularly in patients with acute leukaemiaand bone marrow transplant recipients with fever, the presenceof the CT halo sign strongly suggests invasive pulmonary aspergillosis”.

26. DISCUSSION In 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.

27. DISCUSSION Table .: List of diseases showing the CT halo sign

28. 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.