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Background
An angiomyoma is a rare benign smooth muscle tumour originating from the tunica media of the vessel walls. 1 2 As the histological origin suggests, it can occur in any part of the body with the favoured site being the extremities, particularly lower limbs in females and upper limbs in males. Pain associated with a slowly growing subcutaneous mass is the most common presentation of angiomyomas. 1-3
Angiomyomas have rarely ever been correctly diagnosed clinically or radiologically, first because of their relative rarity of occurrence and, more importantly, due to the paucity of relevant radiological literature. The purpose of this case report is to highlight the imaging findings of angiomyoma and to sensitise clinicians, particularly radiologists, to consider angiomyoma as an important differential in the approach to a painful subcutaneous soft tissue mass.
Case presentation
A 36-year-old man presented with a slow-growing, mildly painful mass around the left knee joint for the past 2 years. There was no history of trauma or difficulty in walking. On examination, a 3x2 cm soft, fluctuant mass was seen on the medial side of the knee along the patellar tendon. The mass lesion was mobile from the underlying bone and tendon with 'slip sign' positive. There was no ulceration or discolouration of the overlying skin and the skin could be easily pinched from the lesion. Temperature and touch sensation of the overlying skin was normal. Thus, a clinical diagnosis of ganglion cyst was made and the patient was referred for an ultrasound examination.
Investigations
Ultrasound revealed a well-defined, oval, homogenously hypoechoic solid mass lesion in the subcutaneous tissue of the medial aspect of knee joint, showing rich internal vascularity on colour Doppler. Subsequently, MRI of the knee was performed revealing a well-defined, smooth and marginated, oval subcutaneous soft tissue mass measuring 3x2.5 cm on the medial aspect of the knee anterior to the patellar tendon. The lesion was hypoisointense to muscle on T1-weighted images and hyperintense on T2-weighted and showed thin interlacing internal septa with a thin peripheral hypointense rim on T2-weighted images ( figure 1 A, B). There was no evidence of any haemorrhage or calcification seen. Postcontrast, there was intense homogenous enhancement and a small vessel was seen leading up to and ending near the superior...