Peh, WCG

Wong, WC

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Title Radiological conference. Bronchogenic cystAuthor(s) Wong, WC; Peh, WCGCitation Hong Kong Practitioner, 1998, v. 20 n. 3, p. 149-152Issued Date 1998URL http://hdl.handle.net/10722/44666Rights Creative Commons: Attribution 3.0 Hong Kong LicenseClinical History:A 75-year-old man complained of abdominal pain for one month. Barium enema and colonoscopy revealed amalignant tumour in the colon. A pre-operative chest radiograph was performed (Figure 1), followed by computedtomography (CT) (Figure 2) to further investigate the incidental radiographic finding.Figure 1: Frontal chest radiograph Figure 2: Unenhanced CT of the thorax (level ofaortic arch)Answeronpage 150What is the diagnosis?a) Aortic arch aneurysmb) Pulmonary metastasisc) Mediastinal lymphadenopathyd) Lateral thoracic meningocoelee) Bronchogenic cystThis radiology case was prepared by: Dr. W.C. Wong,Senior Medical Officer.Professor W.C.G. Pen,Department of Diagnostic Radiology,The University of Hong Kong,Queen Mary Hospital.149Radiological ConferenceRADIOLOGICAL CONFERENCEAnswer:e) Bronchogenic cystRadiological findingsThe chest radiograph (Figure 3) shows a largeoval-shaped soft t issue opaci ty in the r ightmediastinum. Its lateral border is smooth and well-defined, whi le parts of its medial border areinseparable from the adjacent mediastinal soft tissuestructures. The trachea is compressed and displaced tothe left side by this mass. No obvious calcification orcavitation is detected wi th in this lesion. There is noapparent bony erosion, abnormal splaying of ribs ordestruction of vertebral pedicles.Figure 3: Same radiograph as Figure 1 with theaddition of arrows. Convex lateralborder of the right mediastinal mass isarrowed. Part of its medial bordercompresses the trachea (arrowheads).Adjacent bony structures have a normalappearanceFigure 4: Same CT section as Figure 2 with theaddition of arrows. This unenhancedimage shows a well-defined smoothmass ( a r r o w s ) w i t h l o w - d e n s i t yhomogeneous contents. Its relationshipto surrounding structures, such as thetrachea (T) , oesophagus (O) andvertebral body (V), are preciselydemarcatedFigure 5: Same CT section as Figures 2 & 4,taken af ter in travenous contrastadminis trat ion . There is intenseopacification of the major vessels suchas the aorta (A), the left subclavian (S),left common carotid (C) and innominate(I) arteries, and the innominate veins(V). The bronchogenic cyst does notshow any enhancement, except of itsvery thin walls (small arrows)150Hong Kong Practitioner 20 (3) March 1998RADIOLOGICAL CONFERENCE| The radiographic f indings are more precisely| delineated on CT (Figures 4 and 5). In particular,• there is no evidence of calc i f icat ion, cavitation ori invasion of the surrounding mediastinal structures and! vertebrae. Measurement of the CT attenuation numberI confirms the mass to be wholly fluid-filled, withoutj any contrast enhancement. No lung parenchymal lesion| is detected u s i n g the l u n g w i n d o w se t t ings .j Appearances are typical of those of a bronchogeniccyst.DiscussionAortic arch aneurysmAortic aneurysm usually presents as either a roundor oval mediastinal mass, or widening of mediastinumon the chest radiograph of an elderly patient . Thepresence of a p e r i p h e r a l rim of c a l c i f i c a t i o n isI character is t ic and is a usefu l d iagnos t ic s ign . Onc o n t r a s t - e n h a n c e d CT images , the l u m e n of theaneurysm demonstrates intense opacification which iss i m i l a r to tha t of the ad jacen t ar ter ies . In theinvestigation of aortic aneurysms, CT scans can(1) conf i rm the d i agnos i s by showing i ts d i rec torigination from and communication with the aorticlumen,(2) delineate extent of involvement, and(3) detect complications such as thrombosis, dissectionor leakage.The f indings of f luid density of the lesion andcomplete lack of contrast enhancement in our patientj exclude the diagnosis of aortic aneurysm.Pulmonary metastasisMetastases usually disseminates to the lungs byhaematogeneous spread. They have a predilection forthe peripheral subpleural zones of the lungs. However,up to 25% of pulmonary metastases are solitary. Beingin t r a -pu lmonary lesions, pu lmonary metastases arecompletely surrounded by air. This accounts for theirwell-defined borders on chest radiographs, in contrast tomediastinal lesions which always have indistinctness ofpart of their medial border. The "incomplete" borderappearance, typical of a mediastinal lesion, is a helpfulsign in determining the relative location of an intra-thoracic lesion to adjacent structures (Silhouette sign).On CT, pulmonary metastases are most frequently ofsoft-tissue density and usually demonstrate some degreeof e n h a n c e m e n t . The m e d i a s t i n a l l o c a t i o n , CTcharacteristics of the lesion and absence of pulmonarylesions in our patient are features against the diagnosisof pulmonary metastasis.Mediastinal lymphadenopathyOn radiographs, mediastinal lymphadenopathy areu s u a l l y seen as masses wi th s m o o t h l y lobulatedcontours. They may arise in a variety of diseases,i n c l u d i n g u n d e r l y i n g n e o p l a s m , i n f e c t i o n a n dsarcoidosis. Mediastinal lymphadenopathy may be thefirst presentation of mal ignancy such as small cellcarcinoma of lung. In lymphoma, lymphadenopathy isusually bilateral in distribution. Primary infection bytuberculosis leads to enlarged hilar and/or mediastinallymph nodes which together with the primary pulmonaryfocus, constitute the Ghon complex. On CT, lymphnodes are soft tissue in density and display mild degreesof enhancement. This diagnosis is unlikely based on thenon-enhancing cystic appearance of the mediastinallesion.Lateral thoracic meningocoeleA lateral thoracic meningocoele is an extraspinalcerebrospinal fluid (CSF) - filled protrusion of dura andarachnoid mater . It extends la tera l ly through an151Radiological Conferenceenlarged neural foramen and then anteriorly through theadjacent intercostal space into the extrapleural aspect ofthe thoracic gutter. Neurofibromatosis is a frequentassociation, being present in about 85% of affectedpa t ien ts . Expans ion of the s p i n a l c ana l andintervertebral foramen, and associated spinal scoliosis,are frequent findings. Radiographs and CT show theparavertebral lesion and demonstrate any underlyingbony changes. On CT, the lesion is typically of CSF(or fluid) density. Continuity of the lesion with theintra-spinal arachnoid space and skeletal changes areoptimally displayed on CT. None of these findingswere present in our patient.Bronchogenic cystBronchogenic cysts are uncommon, usually isolated,lesions representing a branching abnormality of thet r a c h e o b r o n c h i a l tree d u r i n g i t s e m b r y o g e n i cdevelopment. Most of these lesions arise in themediastinum or hilar region while a small number occurwithin the lung parenchyma. Clinical features arevariable. In infants, these lesions may be discoveredwhen the patient presents as a result of pressure effectson the tracheobronchial airway and oesophagus. Manyolder children and adults are however asymptomaticwith the lesion being incidentally detected on routinechest radiographs, usually before the 4th decade of life.On CT, a sharply-outlined thin-walled cyst is seen.While the cyst contents are usually of homogeneousfluid density, the CT attenuation number may be higherif the cyst is complicated by haemorrhage or infection.On rare occasions, a bronchogenic cyst may undergorapid increase in size as result of haemorrhage, infectionor distension with air. These cysts are usually found inclose proximity to the major airways, with the mostfrequent sites being immediately adjacent to the lowertrachea and the proximal main bronchus. The diagnosisof bronchogenic cyst can be confirmed non-operativelyby needle aspiration of its fluid contents, which shouldbe examined to exclude malignant cells. The diagnosisof bronchogenic cyst in the appropriate c l in ica lcircumstances obviates the need for surgical removal. •References1. Felson B, Felson H: Localisation of intrathoracic lesions by means of thepostero-anterior roentgenogram: the silhouette sign. Radiology 1950;55:363-374.2. Barkovich AJ. Paediatric Neuroimaging. 2nd edition. New York, RavenPress. 1995;pp477-540.3. Armstrong P. The medias t inum. In: Grainger RG, All ison DJ.Diagnostic Radiology. 2nd edition. Edinburgh, Churchill Livingstone,1992;ppl85-211.4. Dee P. Congenital disorders of the lungs and airways. In: Armstrong P,Wilson AG, Dee P, Hansell DM. Imaging of diseases of the chest. 2ndedition. St. Louis, Mosby, 1995;pp609-640.152

Radiological conference. Bronchogenic cyst

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Radiological conference. Bronchogenic cyst

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