252 Fig. 1 Preoperative clinical image Surgical excision is limited to symptomatic osteochon- dromas; as a matter of fact, when the tumor is asymp- tomatic, surgery is not recommended [1, 14]. Indications for surgical resection are pain, deformity, compression to a neurovascular bundle, continuous growth, and suspected malignant transformation [1, 14, 15]. However, when a child presents with a large osteochondroma close to a neurovascular bundle, surgery is indicated to avoid further enlargement, which would make surgery more challenging with a higher risk of neurovascular complications. Pseu- doaneurysm represents an extremely rare complication of J Orthopaed Traumatol (2010) 11:251–255 osteochondroma and typically involves the popliteal and femoral arteries [16, 17]. We present a case of posttrau- matic pseudoaneurysm of the brachial artery occurring after incomplete resection of an osteochondroma and pre- senting as a soft tissue mass. Case report A 14-year-old boy referred to our department for a slowly growing, nonpainful swelling in the medial upper right arm that he had noticed for 8 months. He had undergone partial resection of an osteochondroma in the posterior aspect of the proximal humerus 3 years earlier. Follow-up was unremarkable. He recalled a blunt trauma in his right upper arm while riding a horse; however, swelling presented some weeks later and was characterized by a gradual enlarge- ment. An X-ray was performed and showed a large sessile osteochondroma in the median side of the proximal humerus. An MRI was performed to study the cartilaginous cap of the osteochondroma for malignant transformation and the soft tissues for a soft tissue tumor. MRI was con- sidered suggestive of a soft tissue tumor, and the patient was referred to our department. Physical examination demon- strated a ﬁrm, nonpulsatile, 8-cm swelling in the medial upper arm that was painless during palpation (Fig. 1). There were no signs of vascular or neurologic failure. No enlarged lymph nodes were palpable in the axilla. Bone scan revealed increased uptake at the site of the osteochondroma. MRI performed in our Institute revealed a large, complex mass close to the osteochondroma and the humeral artery. The nonhomogeneous lamellar structure of the mass on MRI, the hyperintensity on T1-weighted sequences, and the reg- ularly capsulated aspect of the contours were suggestive of hematoma–thrombosis (Figs. 2a–c, 3a). Due to these char- acteristics, the hypothesis of malignant transformation was difﬁcult to asses. The MR angiography facilitated the diagnosis, as it showed a pseudoaneurysm arising from the compressed brachial artery with extravasation of contrast Fig. 2 Axial magnetic resonance image (MRI) T2 (a), T1 (b) and T1 turbo spin echo (TSE) fat-saturation (c) sequences. The mass has inhomogeneous signal on T2- (a) and T1- (b) weighted sequence, concentric aspect, regular contours (a, b) and did not diffusely enhance due to the presence of pseudoaneurysm, thrombus, and hematoma (c) 123