J Orthopaed Traumatol (2010) 11:251–255 DOI 10.1007/s10195-010-0116-9 C A S E R E P O R T Pseudoaneurysm overlying an osteochondroma: a noteworthy complication Celeste Scotti • Enrico M. Marone • Laura E. Brasca • Giuseppe M. Peretti • Roberto Chiesa • Alessandro Del Maschio • Gianfranco Fraschini • Francesco Camnasio Received: 29 May 2009 / Accepted: 19 October 2010 / Published online: 20 November 2010 The Author(s) 2010. This article is published with open access at Springerlink.com Abstract Pseuodaneurysms are an extremely rare com- plication of osteochondromas. We describe a case of traumatic pseudoaneurysm of the brachial artery presenting as a soft tissue mass in a patient who was treated for an osteochondroma 3 years earlier. This case demonstrates that radiographic follow-up of large osteochondromas is mandatory and that, in patients with soft tissue masses and a history of osteochondroma, pseudoaneurysms should be included in the differential diagnosis. Keywords Pseudoaneurysm Osteochondroma Soft tissue mass Brachial artery Introduction Osteochondromas are hamartomas derived from an aber- rant subperiosteal germ of the physeal cartilage and grow by normal enchondral ossiﬁcation [1]. They are the most C. Scotti G. M. Peretti G. Fraschini F. Camnasio (&) Department of Orthopaedics and Traumatology, San Raffaele Scientiﬁc Institute, Via Olgettina 60, 20132 Milan, Italy e-mail: camnasio.francesco@hsr.it E. M. Marone R. Chiesa Department of Vascular Surgery, San Raffaele Scientiﬁc Institute, Via Olgettina 60, 20132 Milan, Italy L. E. Brasca A. Del Maschio Department of Radiology, San Raffaele Scientiﬁc Institute, Via Olgettina 60, 20132 Milan, Italy G. M. Peretti Faculty of Exercise Sciences, University of Milan, Via Kramer 4/A, 20129 Milan, Italy common benign tumors of bone, accounting approximately for one third of benign lesions of the skeleton [2]. Never- theless, as they are usually asymptomatic, the real inci- dence is probably higher [3]. Patients usually present during the second decade of life [1]. Malignant transfor- mation has been reported as a very rare complication, accounting for \1% and occurring after puberty more frequently in the limb girdles [1, 4, 5]. In cases of hered- itary multiple osteochondromas, the risk of sarcomatous change is higher [1, 6, 7]. The radiographic appearance of this tumor is often diagnostic: as a matter of fact, the continuity of the lesion with the underlying native bone cortex and medullary canal is pathognomonic of osteochondroma. Computed tomog- raphy (CT) and magnetic resonance (MR) imaging are useful for identifying and studying complications such as malignant transformation, bone fracture, vascular compro- mise, neurologic sequelae, and overlying bursa formation. The thickness of the cartilage cap is typically 1–3 cm in young patients, whereas in adults, it is often only a few millimeters thick or entirely absent [4, 8–10]. A continu- ously growing lesion and a hyaline cartilage cap [1.5-cm thick, after skeletal maturity, suggest malignant transfor- mation. Cortical bone is devoid of mobile protons and shows low signal intensity in all pulse MR sequences, whereas the medullary component has the appearance of yellow marrow. MR imaging is the best radiologic modality for visualizing the effect of the lesion on surrounding structures and evaluating the hyaline cartilage cap. The high water content in nonmineralized portions of the cartilage cap has an intermediate to low signal intensity on T1-weighted MR images and very high signal intensity on T2-weighted images. These features typically allow accu- rate measurement of the cartilage cap thickness and dis- tinction from overlying muscle on MR images [4, 11–13]. 123