Case 74. (27 Mar. 1999)

Diagnosis: Behcet's Disease

Findings
    Chest radiograph shows an ill-defined patchy opacity in the right lower lung zone and a thin-walled cavitary lesion in the left lower lung zone. Focal bulging of the proximal right interlobar artery is also suspected. Blunting of the left costophrenic angle is seen, suggesting pleural thickening with or without small effusion.
Chest CT scans demonstrate mild dilatation of the left interlobar artery with low-density thrombus at the peripheral portion of the lumen. Dilatation with thrombus was also noted in the right interlobar artery (not shown here). Multiple ill-defined airspace nodules are also noted in both lower lobes, and one of them in left lower lobe has cavity. A low-attenuation material (probable thrombus) is seen within the right ventricle. On abdominal CT scan, saccular aneurysm is present in the abdominal aorta.

Brief Review
    Behcet's disease is a rare form of vasculitis of obscure etiology. Any large or small artery, vein, or organ may be involved in an unpredictable combination. According to the criteria set by the International Study Group for Behcet's Disease, the diagnosis is based on the presence of recurrent oral ulcers plus two of the following:
recurrent genital ulcers, eye lesions (anterior or posterior uveitis, retinal vasculitis), skin lesions (erythema nodosum, pseudofolliculitis, papulopustular lesions, acneiform nodules), or a positive pathergy test (pustule formation 24-48 hr after skin prick). Patients are usually 20-30 years old at the time of onset of the disease. The prevalence is considerably higher in Mediterranean countries, the Middle East, and the Far East than in the rest of the world.
Intrathoracic manifestation of Behcet's disease consist mainly of thromboembolism of the superior vena cava and/or other mediastinal veins; aneurysm of aorta and pulmonary arteries; pulmonary infarct and hemorrhage; pleural effusion; and, rarely, myocardial or pericardial involvement, cor pulmonale, and mediastinal or hilar lymphadenopathy.
    Chest radiography is the best diagnostic method for evaluating thoracic involvement in Behcet's disease, and shows mediastinal widening, air-space consolidation, and lung mass. Sudden hilar enlargement or intraparenchymal round opacities is a sign of pulmonary artery aneurysm. CT scan shows that that mediastinal widening was due to
thrombosis or narrowing of the superior vena cava which caused mediastinal edema; that air-space consolidation was due to pulmonary hemorrhage or infarction; and that lung mass was due to aneurysm of the right or left pulmonary artery. They may recur, progress, or resolve, either spontaneously, within a few weeks to several months, or with corticosteroid therapy. Although no comparative studies are available, CT and MR angiography appear to be imaging techniques of choice for evaluating vascular involvement. CT also can demonstrate pulmonary parenchymal changes such as air-space nodules, cavities, and mosaic areas of lung attenuation.
Recently, helical CT findings of pulmonary artery aneurysms during treatment for Behcet¢®?s disease were reported. Pulmonary artery aneurysms may become smaller or disappear with medical treatment. Mural thrombotic changes may be observed during the regression of pulmonary artery aneurysms. Perianeurysmal consolidation and
air-space nodules, and mosaic attenuation areas may disappear during or after treatment.
    Differential diagosis includes Hughes-Stovin syndrome that has indentical histologic and clinical features except for oral and genital ulcers. Both Reiter's syndrome and relapsing polychondritis may complicated by aortitis and aortic aneurysms with some overlapping clinical features. Arterial narrowings and occlusions, producing symptoms
of vascular insufficiencies in Behcet's disease, may clinically mimic Takayasu's arteritis.

References
1. Tunaci A, Berkmen YM, Gokmen E. Thoracic involvement in Behcet's disease: pathologic, clinical, and imaging
features. AJR 1995;164:51-56.
2. Tunaci M, Ozkorkmaz B, Tunaci A, Gul A, Engin G, Acunas B. CT findings of pulmonary artery aneurysms during treatment for Behcet's disease. AJR 1999;172:729-33.
3. Ahn JM, Im JG, Ryoo JW, et al. Thoracic manifestations of Behcet syndrome: radiographic and CT findings in nine patients. Radiology 1995;194:199-203.

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