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Tree-in-Bud Pattern in Neoplastic Pulmonary Emboli

¹ Department of Radiology, Centre Hospitalier Universitaire de Charleroi, 92 Blvd. Janson, B-6000 Charleroi, Belgium.
² Department of Pathology, Cliniques Universitaires de Bruxelles, Hôpital Saint-Luc, 10 Ave. Hyppocrate, B-1200 Bruxelles, Belgium.
³ Department of Radiology, Hôpital Erasme, 808 Rte. de Lennik, B-1070 Brussels, Belgium.

Received July 17, 2000; accepted after revision November 13, 2000.

 
Address correspondence to D. Tack.

Introduction

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The tree-in-bud pattern consists of the association of centrilobular nodules at the extremity of branching linear opacities and has been exclusively described in small airways disorders [1,2,3]. We report a case with a tree-in-bud pattern related to neoplastic pulmonary emboli from an abdominal desmoplastic small round-cell tumor.

Case Report

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A 31-year-old man complained of fatigue, cough, and moderate fever for 2 weeks, and of hemoptysis the previous day. The physical examination elicited only a few abnormal pulmonary sounds, but there was an abdominal mass in the right iliac fossa. The WBC was normal. A helical CT scan of the pulmonary arteries showed bilateral pulmonary emboli in the upper and lower lobes. An abdominal CT scan showed a solid, lobulated, heterogeneous tumor 11 cm in diameter in the retroperitoneum of the right iliac fossa and a thrombus in the inferior vena cava. A biopsy of the abdominal mass was obtained surgically; the inferior vena cava thrombus was neither biopsied nor removed. The histology was typical for a desmoplastic small round-cell tumor. The pulmonary emboli were treated with vitamin K inhibitors, and therapy with cisplatin, etoposide, and epirubicin was begun. Four months after onset, the patient's dyspnea had progressively increased. A new enhanced helical CT image of the chest showed an increase in the number and size of intraarterial emboli when compared with previous scans. Indirect signs of pulmonary hypertension were confirmed by pressure measurements (mean pulmonary pressure, 50 mm Hg). An inferior vena cava filter was inserted. The size of the abdominal mass remained essentially the same throughout the 6 months of therapy. The retroperitoneal mass was removed. Three weeks after surgery, the patient experienced very severe dyspnea. Helical CT images were then obtained that showed beaded central and peripheral pulmonary arteries and a tree-in-bud pattern (Fig. 1A). The patient died the next morning. The autopsy revealed intraarterial macroscopic tumor emboli in both the central and peripheral portions of the lungs, up to the centrilobular arteries (Fig. 1B). The inferior vena cava filter was also obstructed by tumor tissue.

View larger version (115K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —31-year-old man with neoplastic pulmonary emboli from abdominal desmoplastic small round-cell tumor. CT scan obtained with 5-mm-thick collimation and photographed with lung window. Enlarged and beaded segmental and subsegmental pulmonary arteries (A) are seen in right middle and lower lobes. Tree-in-bud pattern is visible in peripheral zone of right middle lobe (arrow).

View larger version (147K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —31-year-old man with neoplastic pulmonary emboli from abdominal desmoplastic small round-cell tumor. Photomicrograph of peripheral pulmonary arteries near pleural surface (arrowheads). Centrilobular arteries are filled with tumor cells (arrows).

Discussion

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To our knowledge, the branching of centrilobular micronodules resulting in a tree-in-bud pattern has not been described in vascular disorders, but only in airway diseases [1,2,3]. This pattern consists of centrilobular micronodular and linear branching opacities caused by dilatation and filling of the small airways. Because pulmonary arteries are parallel to the bronchi, this pattern should also be seen in arterial disorders characterized by vascular dilatation or filling as shown in this patient. The photograph in Figure 1B shows the arterial filling in a peripheral location, similar to the micronodules in the tree-in-bud pattern. Nonoccluded peripheral arteries in chronic pulmonary emboli or other vascular diseases of the lungs (e.g., vasculitis, pulmonary hypertension) may be dilated and characterized by centrilobular opacities on high-resolution CT [2]. However, these micronodular centrilobular opacities are not branching and do not result in a tree-in-bud pattern.

The beaded appearance of central pulmonary arteries filled with tumor emboli as in Figure 1A has been described by Shepard et al. [4]. They also described peripheral nodules, but not with a tree-in-bud appearance. The beaded arteries correspond to the deformity of the vessel walls by the impacted tumor emboli. The tree-in-bud pattern seen in the present case may be considered to be the result of the same process, applied to the peripheral pulmonary vasculature.

Pulmonary emboli in the lungs may differ according to the size of emboli. Microscopic emboli are located in the capillaries; their clinical features are pulmonary hypertension and acute cor pulmonale. Macroscopic tumor embolization has clinical presentation similar to thromboembolic disease. This diagnosis is difficult and is made correctly in only a small proportion of the cases [5]. It is commonly believed that microscopic tumor emboli are the source of lymphangitic carcinomatosis. CT features of lymphangitic carcinomatosis include peribronchovascular thickening, which may be difficult to distinguish from vascular enlargement, thickened septal lines, and micronodules. In our patient, such septal thickening was absent on CT scans as well as on pathology specimens (Fig. 1B), and did not show lymphangitic tumor spread.

Renal cell carcinoma is the most frequent origin of tumor emboli in the pulmonary arteries. A large variety of tumors have been described as potential sources of tumor emboli. The desmoplastic small round-cell tumor has not yet been described as potentially venoinvasive [6].

In summary, tumor embolization in the pulmonary arteries may present with patterns of vascular enlargement including the tree-in-bud pattern, which should no longer be considered specific for bronchiolar disease.

References

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1. Gruden JF, Webb WR, Warnock M. Centrilobular opacities in the lung on high resolution CT: diagnostic considerations and pathologic correlation. AJR 1994;162:569 -574[Abstract/Free Full Text]
2. Collins J, Blankenbaker D, Stern EJ. CT patterns of bronchiolar disease: what is "tree-in-bud"? AJR 1998;171:365 -370[Free Full Text]
3. Gruden JF, Webb WR, Naidich DP, McGuinness G. Multinodular disease: anatomic localization at thin-section CT—multireader evaluation of a simple algorithm. Radiology 1999;210:711 -720[Abstract/Free Full Text]
4. Shepard JA, Moore EH, Templeton PA, McLoud TC. Pulmonary intravascular tumor emboli: dilated and beaded peripheral pulmonary arteries at CT. Radiology 1993;187:797 -801[Abstract/Free Full Text]
5. Goldhaber SZ, Dricker E, Buring JE, et al. Clinical suspicion of autopsy-proven thrombotic and tumor pulmonary embolism in cancer patients. Am Heart J 1987;114:1432 -1435[Medline]
6. Pickhardt PJ, Fisher AJ, Balfe DM, Dehner LP, Huettner PC. Desmoplastic small round cell tumor of the abdomen: radiologic—histopathologic correlation. Radiology 1999;210:633 -638[Abstract/Free Full Text]

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