J Orthopaed Traumatol (2010) 11:251–255 The case presented here is quite unusual, but the clinical presentation reﬂects the typical case found in the literature: an adolescent male, already treated for a large osteochon- droma in an area with high risk of neurovascular com- pression, reporting a sport-related injury. The differential diagnosis included malignant transformation and Ewing’s sarcoma, so we performed contrast-enhanced MRI and angiographic MRI to rule out these diagnoses. MRI is mandatory for evaluating such atypical masses in children and adolescents [22]. Moreover, malignant transformation is extremely rare in adolescence [1], and Ewing’s sarcoma often presents with other signs and symptoms, such as fever, increased serum lactate dehydrogenase and eryth- rocyte sedimentation rate, leukocytis, and anemia [23], which were not present in our patient. Therefore, according to the patient’s history of blunt trauma, to MRI features, and to the surgical ﬁndings of close proximity of the pseudoaneurysm to a cartilaginous spur, the diagnosis was traumatic pseudoaneurysm caused by an osteochondroma. This case shows how important it is to perform adequate resection of a large osteochondroma arising in close proximity to neurovascular structures. On the other hand, osteochondromas in adolescence may spontaneously regress [15] or recur, even after adequate resection, so that a radiographic follow-up is mandatory [1]. In conclusion, we emphasize the importance of correct treatment and follow-up of large osteochondromas in dangerous regions in order to avoid such complications. We also encourage the orthopedic oncologist to include pseudoaneurysms in the differential diagnosis of soft tissue masses, especially when there is a history of osteochon- droma resection. Conﬂict of interest None. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. Campanacci M (1999) Exostosis. In: Campanacci M (ed) Bone and soft tissue tumors, 2nd edn. Springer-Verlag, Padova, pp 179–196 2. Porter DE, Simpson AH (1999) The neoplastic pathogenesis of solitary and multiple osteochondromas. J Pathol 188:119–125 3. Stieber JR, Pierz KA, Dormans JP (2001) Hereditary multiple exostoses: a current understanding of clinical and genetic advances. Univ PA Orthop J 14:39–48 255 4. Garrison RC, Unni KK, McLeod RA et al (1982) Chondrosar- coma arising in osteochondroma. Cancer 49(9):1890–1897 5. Ahmed AR, Tan TS, Unni KK et al (2003) Secondary chondro- sarcoma in osteochondroma: report of 107 patients. Clin Orthop Relat Res 411:193–206 6. Solomon L (1974) Chondrosarcoma in hereditary multiple exostosis. S Afr Med J 48(16):671–676 7. Pierz KA, Womer RB, Dormans JP (2001) Pediatric bone tumors: osteosarcoma, Ewing’s sarcoma, and chondrosarcoma associated with multiple hereditary osteochondromatosis. J Pediatr Orthop 21:412–418 8. Mirra JM (1989) Benign cartilaginous exostoses: osteochon- droma and osteochondromatosis. In: Mirra JM (ed) Bone tumors: clinical, radiologic and pathologic correlations Vol 2. Lea & Febiger, Philadelphia, pp 1626–1659 9. Lange RH, Lange TA, Rao BK (1984) Correlative radiographic, scintigraphic, and histological evaluation of exostoses. J Bone Joint Surg Am 66(9):1454–1459 10. Kenney PJ, Gilula LA, Murphy WA (1981) The use of computed tomography to distinguish osteochondroma and chondrosarcoma. Radiology 139(1):129–137 11. Lee JK, Yao L, Wirth CR (1987) MR imaging of solitary os- teochondromas: report of eight cases. AJR Am J Roentgenol 149(3):557–560 12. Aoki J, Sone S, Fujioka F et al (1991) MR of enchondroma and chondrosarcoma: rings and arcs of Gd-DTPA enhancement. J Comput Assist Tomogr 15(6):1011–1016 13. De Beuckeleer LH, De Schepper AM, Ramon F (1996) Magnetic resonance imaging of cartilaginous tumors: is it useful or nec- essary? Skeletal Radiol 25(2):137–141 14. Bottner F, Rodl R, Kordish I et al (2003) Surgical treatment of symptomatic osteochondroma. A three- to eight-year follow-up study. J Bone Joint Surg Br 85(8):1161–1165 15. Arkader A, Dormans JP, Gaugler R et al (2007) Spontaneous regression of solitary osteochondroma: reconsidering our approach. Clin Orthop Relat Res 460:253–257 16. Wiater JM, Farley FA (1999) Popliteal pseudoaneurysm caused by an adjacent osteochondroma: a case report and review of the literature. Am J Orthop 28:412–416 17. Vasseur MA, Fabre O (2000) Vascular complications of osteo- chondromas. J Vasc Surg 31(3):532–538 18. Tobias AM, Chang B (2004) A rare brachial artery pseudoan- eurysm 13 years after excision of a humeral osteochondroma. Ann Plast Surg 52(4):419–422 19. Gerrand CH (1997) False aneurysm and brachial plexus palsy complicating a proximal humeral exostosis. J Hand Surg [Br] 22(3):413–415 20. Villanueva-Garcia E, Bas-Hermida P, Espinosa-Lledo C (1995) Pseudoaneurysm of the brachial artery caused by an osteochon- droma: a report of two cases. Int Orthop 19:248–250 21. Koenig SJ, Toth AP, Martinez S et al (2004) Traumatic pseu- doaneurysm of the brachial artery caused by an osteochondroma, mimicking biceps rupture in a weightlifter: a case report. Am J Sports Med 32(4):1049–1053 22. Brisse H, Orbach D, Klijanienko J et al (2006) Imaging and diagnostic strategy of soft tissue tumors in children. Eur Radiol 16(5):1147–1164 23. Bacci G, Balladelli A, Forni C et al (2007) Ewing’s sarcoma family tumours. Differences in clinicopathological characteristics at presentation between localised and metastatic tumours. J Bone Joint Surg Br 89(9):1229–1233 123