Eur. Radiol. 5, 666-668 (1995) © Springer-Verlag 1995

European Radiology

Chest radiology Intramural hydatid cysts of pulmonary arteries: CT and MR findings H. Alper, N. Yiinten, R. N. ~ener Department of Radiology, Ege University Hospital, Bornova, Izmir, TR-35100, Turkey Received 14 October 1994; Revision received 4 April 1995; Accepted 19 May 1995

Case report

Introduction Hydatid disease most commonly affects the liver and lungs, and approximately 10-15 % of the lesions are seen elsewhere in the body. Rarely, vital organs, such as the heart and brain, can be affected [1-7]. Although involvement of the walls of the cardiac chambers, interventricular septum, and pericardium have been reported as sites of location of hydatid cysts [1-4], to the best of our knowledge, intramural pulmonary artery involvement with subsequent occlusion of the lumen has not been reported previously. The condition apparently resulted from embryos of the parasite, which entered the "vasa vasorum" of the involved arteries.

Correspondence to: R. N. Sener

A 55-year-old man was referred to our institution for dyspnea apparently increasing with activity, which he felt more during the past 6 months. His history revealed several operations for liver and lung hydatid disease 7 years prior. These were shown to be due to Echinococcus granulosus. A right lower lobectomy was performed for a large lung cyst, and later he was again operated on for a bronchobiliary fistula. A chest radiogram showed changes consistent with previous lobectomy, several nodular parenchymal lesions consistent with hydatid cysts, and a prominence of the left lower lobe artery. On CT low-density lesions were evident in the right main pulmonary artery and in the artery of the left lower lobe, the latter with a well-defined oval shape and with water density (Fig. i a,b). On M R the latter lesion showed hypointensity on Tl-weighted images (Fig. i c) and hyperintensity on T2-weighted images (such as cerebrospinal fluid) suggesting a cystic lesion (Fig. i d). The lesion in the right main pulmonary artery remained moderately hyperintense on all sequences, suggesting thrombosis (Fig. 1 c, d). An MR angiogram revealed occlusion of the relevant arteries (Fig. le). A conventional pulmonary angiography revealed total occlusion of these arteries (Fig. i f). An operation was undertaken by total circulatory arrest. It was noted that the right main pulmonary was dissected first and a thrombus was evacuated from this artery and from the artery of the upper lobe. There was no thrombus in the left main pulmonary artery; however, a soft lesion was observed within the lumen of the left lower lobe artery and was left intact because this lesion was suggested to be a hydatid cyst based on preoperative CT and MR imaging findings. Histopathological examination of the thrombus material obtained from the right main pulmonary artery revealed hemorrhage, fibrin, necrosis, and intermixed pieces of parasitic membranes. The pathologist suggested a ruptured intramural hydatid cyst complicated with thrombosis.

H. Alper et al.: Intramural hydatid cysts of pulmonary arteries

Fig.la-f. A 55-year-old man with intramural hydatid cysts of pulmonary arteries, a A CT scan shows intraluminal hypodensities within the right main pulmonary artery (arrow), and the artery of the left lower lobe (curved arrow). Note that the latter lesion is spherical in shape and causes expansion of the artery. It had water density, b A CT scan at lower level than a again shows the cystic lesion within the left lower lobe artery (curved arrow). A septation is seen in the lesion, c A Tl-weighted MR image shows hyperintensity of the lesion within the right main pulmonary artery (star) suggesting thrombosis (see ti). The lesion in the left lower lobe artery is hypointense (asterisk; this was best seen on original film; see d). d A T2-weighted MR image shows the lesion in the right

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main pulmonary artery again to be hyperintense (thrombosis; star). At operation parasitic membranes of a ruptured hydatid cyst intermixed with thrombosis were found. Note that the lesion in the left lower lobe artery is now hyperintense suggesting a fluid-filled structure (hydatid cyst; arrow). This lesion was left intact at operation to avoid rupture, e Flow-sensitive MR image (two-dimensional gradient-echo sequence; flip angle/TR/TE/number of excitations: 30/30/12/1) shows occlusion of the involved arteries, f Conventional pulmonary angiography shows total occlusion of the right main pulmonary artery and the artery of the left lower lobe. Only the artery of the left upper lobe is patent

668 Discussion With regard to involvement of the cardiovascular system with hydatid disease, several reports are available on cardiac involvement, which reportedly comprises 0.02-2 % of cases. Most often the left ventricular wall is affected and other locations are the interventricular septurn, pericardium, right ventricle, and atriums, with decreasing frequency [1-4]. To our knowledge, intramural pulmonary artery involvement has not been reported previously. It seems that the only explanation for how the cysts were lodged within the walls of the pulmonary arteries in our patient is that the embryos of the parasite must have entered the walls of the arteries via the "vasa vasorum." Then they grew slowly toward the lumina to completely occlude them, enabling sufficient time for development of sufficient perfusion from the bronchial arteries. The patient's chronic symptoms (dyspnea for several months) support this conjecture. We believe that this represents a previously unrecognized mechanism for dissemination of echinococcosis. The M R appearance of a hydatid cyst is usually characteristic of a spherical lesion with signal intensity identical to cerebrospinal fluid, and it shows a hypointense rim on T2-weighted M R images, which is believed to represent the pericyst consisting of dense fibrous capsule from reactive host tissue [1-4]. In our patient the signal pattern of the lesion involving the left lower lobe artery was consistent with this (Figs. 1 c, d). On CT uncomplicated hydatid cysts usually show low attenuation values (like water), and this was the case for the left lower lobe artery lesion (Figs. 1 a, b). The hydatid cyst within the wall of the right main pulmonary artery was ruptured and intermixed with thrombus. Therefore, it had higher values on CT (Figs. 1 a,b), and its signal was high on T1- and T2-weighted M R images (Fig. i c, d). With regard to the differential diagnosis, it has been reported that an intraluminal filling defect on CT can be seen in pulmonary thromboembolism and primary

H. Alper et al.: Intramural hydatid cysts of pulmonary arteries pulmonary artery sarcoma [8, 9]. The signal pattern of such lesions does not follow that of cerebrospinal fluid on MR imaging, and in case of a tumor enhancement is expected after administration of contrast medium [9]. A lesion with cerebrospinal fluid intensity on CT and M R is likely to be a cystic structure such as the lesion in the left lower lobe artery in our patient (Figs. lc, d). It is highly probable that this lesion represented an intramural hydatid cyst (with subsequent complete occlusion of the lumen), because the patient was a known hydatid disease victim and because hydatid cysts with similar intensity patterns on M R have been reported in the walls of the heart.

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