Teaching Case

A 52-year-old gentleman, with hypertension and atrial fibrillation (anti-coagulated with apixaban), presented with left-calf pain following a fall into a badger hole. Clinical examination showed gross swelling of the left calf, loss of ankle plantar flexion, and positive Simmonds# test. An ultrasound of the left calf was arranged.

Initial duplex ultrasound of the left calf showed a partial thickness tear of the left Achilles tendon. Deep to the tendon at its anterior mid-portion, a vascular lesion was seen visible with a characteristic ying-yang sign in keeping with pseudoaneurysm (Fig. 1). A subsequent CT angiogram revealed the pseudoaneurysm arising from a small perforating branch of the posterior tibial artery, measured 28 x 23 x 48 mm with a small arterial enhancing lumen measuring 17 x 14 x 13 mm (Fig. 2). An MRI confirmed the presence of a partial-thickness Achilles tendon rupture, with 70% fibre disruption (Fig. 3).
Following consultation in interventional radiology, the patient underwent ultrasound-guided thrombin injection (0.2ml) into the pseudoaneurysm resulting in complete thrombosis (Fig. 4). The patient was managed conservatively for the Achilles tendon injury.

Pseudoaneurysm of the crural arteries is a rare condition, predominately caused by iatrogenic intervention, trauma, or collagen vascular disorders [1-3]. A review of the literature demonstrates this is the first case to describe a pseudoaneurysm associated with an Achilles tendon tear following blunt trauma. In this case, the patient denied any previous percutaneous instrumentation or endovascular treatment. There were no identifiable risk factors for a collagen vascular disorder. The patient did report past repetitive football-related injuries.

Duplex ultrasonography is the mainstay imaging modality for diagnosis and evaluation of an extremity pseudoaneurysm. The pseudoaneurysm demonstrates a characteristic ‘to and from’ Doppler waveform on ultrasound, described as the ying-yang sign [4]. CT angiogram may be used for further evaluation when ultrasound is inconclusive or endovascular treatment is planned. In this case, extensive soft tissue oedema limited sonographic evaluation of the origin of the pseudoaneurysm and a CT was performed.

Contained by the adventitia and perivascular soft tissue, small pseudoaneurysms may undergo spontaneous thrombosis and can be managed conservatively. However larger lesions are often symptomatic and in the setting of continuous anticoagulation, as in this case, usually require treatment to prevent enlargement, rupture and subsequent potential leg ischaemia. Treatment options range from ultrasound-guided compression, thrombin injection, endovascular coiling or stenting, and surgical ligation when the limb is threatened [5]. Following discussion with our vascular surgery colleagues and consultation with the patient, thrombin injection under ultrasound guidance was performed with an excellent outcome as confirmed on repeat ultrasound with near complete absence of flow at the aneurysm neck. There were no adverse clinical sequelae, and the patient made a good recovery.  

In conclusion, pseudoaneurysm of the lower crural arteries is a rare entity following blunt trauma. Initial investigation with ultrasound is recommended in all patients with symptomatic calf swelling which may reveal the presence of a characteristic vascular lesion or guide further evaluation with cross-sectional imaging. Treatment should be evaluated on a case-by-case basis, following multi-disciplinary discussion with interventional radiology and vascular surgery, as well as appropriate consultation with the patient.

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