A 25-year-old woman presented with 9 months history of swelling of the anterior aspect of the left knee associated with pain during knee flexion. There was no history of traumatic injury, complaints in other joints or systemic symptoms.
The initial plain film demonstrated opacification of the infrapatellar (Hoffa’s) fat pad, which contained a small ovoid calcification. No other relevant radiographic abnormalities were noted.
MRI showed a lobulated mass in the infrapatellar fat pad, with invasion of the patellar tendon anteriorly. This lesion demonstrated marked high signal intensity on fluid-sensitive sequences and intermediate signal on T1-weighted images. Fluid-fluid levels and an internal small focus of low signal in all sequences was also noted, in keeping with the phlebolith depicted in the plain film.
There was no joint effusion, marrow signal abnormality or other abnormalities.
Synovial haemangioma is an uncommon benign vascular malformation that occurs most frequently around the knee, but has also been reported in other joints and tendon sheaths. It may occur as a focal or diffuse lesion. The average age of onset is adolescence and early adulthood [1].
The initial clinical presentation often includes pain, swelling, mechanical symptoms and haemarthrosis. On examination, the mass is frequently palpable, compressible and spongy [2].
Plain films are normal or non-specific, often demonstrating a soft tissue mass. Phleboliths are occasionally seen.
MR imaging features of synovial haemangioma are frequently very characteristic. Generally there is a lobulated mass, with low to intermediate signal on T1 weighted images and marked hyperintensity on fluid sensitive sequences, reflecting blood pooling in vascular spaces. Thin hypointense fibrofatty septa can be present. Identification of fluid/fluid levels in the vascular spaces and small rounded signal voids compatible with phleboliths are not uncommon [3]. Siderotic synovitis associated with repetitive episodes of haemarthrosis presents with synovial thickening and hypointensity, more pronounced on gradient echo images. Sometimes the lesion can infiltrate the surrounding soft tissues.
Treatment usually consists of open or arthroscopic surgical excision. Recurrence is common in cases of diffuse synovial haemangioma [4].
Synovial haemangioma
Based on the provided X-ray and MRI images of the left knee, the following main features can be observed:
Considering the patient’s age (25 years), clinical symptoms (9 months of anterior knee swelling accompanied by pain during activity), and the above radiological features, the following differential diagnoses can be considered:
Taking into account the patient’s young age, duration of symptoms, and imaging findings (in particular, the lobulated lesion showing slightly low T1 signal and intense high T2 signal with visible vascular septations), the most likely diagnosis is synovial hemangioma (Synovial Haemangioma).
Should further exclusion of other pathologies be necessary, arthroscopic evaluation and histopathological examination can be utilized for confirmation.
Even though synovial hemangioma is a benign lesion, it can repeatedly bleed and cause joint symptoms and functional impairment; therefore, active treatment is recommended. Typical management options include:
During rehabilitation, the knee should be closely monitored for any increase in swelling or pain, and prompt medical evaluation is advised if symptoms worsen significantly.
Disclaimer: This report is based solely on the currently provided imaging and clinical history, and does not replace in-person consultation or professional medical judgment. In the event of any concerns or worsening of symptoms, please seek medical attention or consult a specialist without delay.
Synovial haemangioma
