Teaching Case

2-year-old patient came to our attention for acute right-leg pain, palpable muscle thickening and walking impairment due to painful leg press-up referred after a mild effort.
There was no significant clinical history.

On admission, plain film revealed cortical bone sclerosis of right femoral diaphysis (Fig.1). Ultrasound showed an inhomogeneous mass, 8x3 cm on maximum diameter, placed into the deep muscle-layer of the thigh (Fig.2a,b). Lesion appeared well defined, quite squeezable using the US-convex probe with clear colour Doppler signals (Fig.2c,d). MR examination was performed: lesion appeared isointense in SE T1W images (Fig.3a), inhomogeneously hyperintense on STIR sequences (Fig.3b,c) with multiple signal-void areas on FFE T2W sequences (Fig.3d), after paramagnetic cm iv-administration a significant inhomogeneous enhancement was also achieved. Moreover, the involved muscle appeared replaced by the lesion rather than really compressed (Fig.3e,f). CT examination showed the diffuse cortical bone thickening better without any appreciable cortical breaks (Fig.4).
Based on these findings, differential diagnosis of mesenchimal sarcoma could not be excluded, for this reason surgical biopsy was performed. Finally, artero-venous malformation was confirmed on histologic evaluation (Fig.5).

The International Society for the Study of Vascular Anomalies classification, based on cellular features, subdivides vascular anomalies in vascular tumours and vascular malformations (simple or combined). Jackson et al classify haemangiomas, vascular malformations, and lymphatic malformations on the basis of vascular dynamics. Malformations with arterial components are considered high-flow lesions and those without arterial components are considered low-flow lesions.
US is an essential, noninvasive tool used to examine superficial vascular lesions. Colour Doppler imaging permits analysis of arterial and venous flow and measurement of flow velocities, it also results in an important method for monitoring patients who have undergone therapy, but it is limited in the assessment of deep lesions and lesions adjacent to interfering air or bone.
CT with iv cm-administration is useful for assessment of vascular malformations; to estimate the presence of calcification or thrombus, distal runoff (when lesions are located in the extremities) and concomitant lesions. Because CT involves considerable exposure to ionising radiation and provides less information about blood flow, MR imaging has replaced CT in the evaluation of vascular malformations.
MR imaging is the most valuable modality for the classification of vascular malformations. It depicts the anatomic relations between the vascular lesion and adjacent organs. Slow-flow venous malformations have high signal intensity on T2-weighted images, whereas high-flow arteriovenous malformations and fistulas contain a signal void. Phleboliths and calcifications also show signal voids in all image sequences. Dynamic study with a gradient pulse sequence is useful for evaluating the flow velocity (slow, intermediate, or high) of lesions and in monitoring patients who have undergone therapy.