T2 weighted (a) and STIR (b) images
Gradual filling with contrast was observed during the course of examination. Prominent venous structure was noted at the cranial border of the formation. MRI signs of aggressive growth such as oedema were absent. Furthermore, ultrasound with colour Doppler was performed, confirming low-flow vascular malformation with predominantly venous signal.
Abnormal proliferation of blood vessels is distinctive for common venous malformations  - benign vascular lesions, which typically manifest themselves in first two or three decades of life [2, 3]. They may present in any vascularized tissue, most commonly in subcutaneous and mucosal tissues. On the other hand, intramuscular venous malformations, arising from skeletal muscles, are rare - they account for less than 1% and only 14% of these occur in head and neck musculature [2-7]. Most frequently affected muscle is the masseter muscle, while the involvement of the temporal muscle is extremely rare . Moreover, only 27 cases of venous malformations in the temporal muscle were reported till July 2014 . Etiologically, there have been hypotheses of both congenital and postnatal causes, such as trauma and hormonal change [2, 5].
Intramuscular common venous malformations usually presents with pain and discomfort or cause cosmetic deformities due to progressive enlargement [2, 3, 6]. Since they are infrequent, located in relatively deep tissues and have quite uncharacteristic presentation, these formations may be challenging to diagnose .
MRI is the imaging modality of choice, being able to differentiate the lesion and its vascular structure from surrounding tissues. These lesions are located within the muscle and appear isointense on T1-weighted images and hyperintense on T2-weighted images [2, 5, 6, 7]. Phleboliths, which are presented in around 20% of intramuscular lesions, appear mostly hypointense on T1/T2-weighted images . These formations have endothelial-lined vascular channels with fibrous or fatty tissue in-between. Also hemosiderin depositions or thrombi may be present [2, 5]. Ultrasound with Colour Doppler sonography is useful for distinguishing from other pathological lesions, clearly demonstrating blood flow characteristics . CT and arteriography are possibilities as well, but are less commonly used [2, 5].
Different treatment options exist, from simple observation, irradiation (inadvisable for children) and sclerosation to corticosteroids, embolization and surgical excision [2, 5]. Treatment approach should be individualized, but nevertheless, surgical excision is the treatment of choice [5, 6]. Long term follow-up after excision is advised due to relatively high recurrence rate (9-28%) of these lesions [2, 6, 7].
Intramuscular common vascular malformations arising from temporal muscle are very rare. These lesions can be fairly confidently diagnosed by using MRI, however ultrasound may be helpful as well, revealing blood flow characteristics.
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