A 42-year-old woman suffered from repeated episodes of inflammatory right knee pain with associated swelling for ten years.
The therapeutic effect of joint aspiration was transient.
Clinical examination showed a painful knee on the medial and inferior aspect of the patella at the femoro-patellar joint, and associated swelling.
Knee radiographs revealed a joint effusion with a mass in the Hoffa's fat pad (Fig. 1a, 1b).
MRI showed a lobulated intra-articular mass in the infra-patellar pouch, hypointense on T1WI without intralesional fat (Fig. 2a) and homogeneously hyperintense on T2WI (Fig. 2b), with hypointense linear structures throughout the mass in keeping with vascular structures. No haemosiderin deposits were identified (Fig. 2c).
After injection of gadolinium contrast medium, marked enhancement was seen (Fig. 2d).
The lesion invaded the inferior aspect of the patella.
There was associated synovial enhancement and joint effusion.
CT confirmed invasion of the patella by the lesion (Fig. 3a, 3b) and subsequent CT guided percutaneous biopsy revealed a vascular malformation (Fig. 3c).
The patient underwent surgical arthroscopic excision of the lesion and histological examination confirmed a cavernous haemangioma with venous malformation.
Soft-tissue haemangiomas are commonly encountered benign vascular tumours. Children and adolescents are most frequently affected [1, 2].
Haemangiomas involving the synovium are rare compared to other localisations (cutaneous, subcutaneous, intramuscular), representing only 1% of all haemangiomas. The knee is the most commonly affected joint (60%), especially on the supra-patellar aspect [3].
In contradistinction to cutaneous haemangiomas, which are readily diagnosed because they cause discolouration of the skin [1], diagnosis of deep-seated haemangiomas is difficult to make without imaging [2, 4].
Patients with joint haemangiomas present with pain, swelling, spontaneous haemarthrosis [1, 2, 5], and occasionally limitation of movement. They can, however, be asymptomatic [3].
Plain film findings are not specific [5], including joint effusion, mass effect, occasional phleboliths and bone erosion in advanced stages [6]. In some cases, plain films can also be normal [2, 3, 7].
MRI is the modality of choice for diagnosing joint haemangiomas.
Typical imaging findings include intermediate signal on T1WI [2, 4, 5, 6], and heterogeneous signal on T2WI with multiple areas of high-signal representing vascular structures containing slow-flowing or stagnant blood that resemble a bunch of grapes [2, 3, 4, 5, 6]. After injection of gadolinium contrast, there is usually heterogeneous enhancement [6].
Sometimes, a peripheral high-signal-intensity is observed on T1WI, corresponding to intra-lesional fat [2, 4].
Intra-lesional fluid-fluid levels can be seen on T2WI, as well as thrombosis, appearing as a round low-signal-intensity resembling a phlebolith [4, 6].
Our case was atypical, showing hypointense linear structures on T2WI, representing high flowing blood.
MR imaging can also detect osseous changes such as periostal, cortical or medullary reaction [1, 3], as well as invasion of the menisci and surrounding tissues [3].
Careful analysis of the lesion extent on MR imaging is very useful to decide which surgical approach should be chosen (arthroscopic or open excision).
Percutaneous biopsy is usually not required before surgery if MRI findings are characteristic [8]. However, in more atypical cases, the decision to perform a pre-surgical biopsy is often made at a multidisciplinary team meeting.
Histopathology findings are variable ranging from cavernous/venous/or mixed synovial haemangioma to nonspecific synovitis. Fibrofatty septa are often seen [2].
In conclusion, synovial haemangiomas are rare benign tumours that most commonly affect the knee joint. MRI imaging is key to the diagnosis, permitting characterization of the lesion and to delineate disease extension. The final diagnosis is made by histological examination of the biopsy or surgical specimen.
Synovial haemangioma of the knee.
1. On the anteroposterior and lateral X-rays of the knee, there is mild soft tissue swelling around the right knee joint, with the joint space essentially preserved. There is no obvious sign of bone erosion or destruction, and no apparent osteophyte formation or calcification.
2. CT reveals a soft tissue density image located suprapatellar or alongside the patella, with relatively clear margins. Some areas show heterogeneous densities; on close inspection, small low-density foci or vascular channel-like structures may be observed. There is no significant bony destruction, only mild cortical indentation beneath the articular surface.
3. MRI provides the most critical diagnostic information for this condition: on T1-weighted images, the lesion typically appears as intermediate or low signal intensity, while on T2-weighted images it shows a high-signal region, with heterogeneous high-signal areas and linear low-signal bands indicating blood vessels or flow voids. After contrast administration, it demonstrates marked enhancement in multiple regions or patchy areas. The lesion is mainly located in the synovium around the patella (or synovial structures of the knee joint) and may invade surrounding soft tissue, forming a mass or grape-like clusters.
Based on the patient’s 10-year history of recurrent pain and swelling, combined with the above imaging findings, possible diagnoses include:
In summary, synovial haemangioma is more consistent with the heterogeneous T2 high signal and vascular flow signal characteristics observed here, and it correlates well with the clinical presentation of recurrent pain and swelling.
Taking into account the patient’s age, a ten-year disease course with recurrent joint swelling and pain, along with MRI findings of heterogeneous T2 high signal, marked enhancement post-contrast, and possible vascular channels, the most likely diagnosis is
Synovial haemangioma of the knee joint.
If uncertainty remains, a multidisciplinary team discussion followed by arthroscopic or open surgical biopsy may be considered for further confirmation.
Surgical Intervention: For patients with significant symptoms and a confirmed or highly suspected synovial haemangioma, arthroscopic or open surgical resection is the primary treatment. Intraoperative identification of the lesion’s boundary is crucial to avoid residual tissue.
Conservative Management: If the lesion is small and symptoms are mild, oral analgesics and anti-inflammatory medications may be attempted while monitoring for lesion progression; however, long-term efficacy is often limited.
Postoperative Management: In the early postoperative phase, immobilization and cold therapy help reduce joint swelling. When necessary, joint aspiration under professional supervision can be performed for decompression.
Rehabilitation Principles: Focus on protecting the joint and gradually restoring range of motion and muscle strength, adhering to a progressive and individualized approach.
FITT-VP Example:
• Frequency: Begin with 3-4 sessions weekly of low-intensity joint movement exercises, increasing to 5 per week as tolerated.
• Intensity: Start with low-intensity isometric training (e.g., straight leg raises, quadriceps contraction with the knee slightly flexed), and gradually progress to moderate resistance exercises. If significant pain occurs, reduce the intensity appropriately.
• Time: Each session can start at 10-15 minutes, gradually increasing to 20-30 minutes. For sets, aim for 5-10 repetitions with a 30-second to 1-minute rest between sets.
• Type: In early stages, perform non-weight-bearing or light weight-bearing activities, such as seated or supine active range of motion exercises. In later stages, introduce weight-bearing flexion and extension training in a standing position, stationary cycling, or swimming.
• Progression: Once joint stability improves and pain subsides, gradually increase weight-bearing and range of motion. Eventually, include strengthening and proprioceptive training.
• Volume and Pattern can be adjusted according to the patient’s condition, ensuring no significant discomfort or acute exacerbation of pain.
Precautions: If severe pain, bleeding tendency, or significant cardiopulmonary issues are present, reduce exercise intensity and seek medical review promptly.
This report is a reference analysis based on the available medical history and imaging data, and it cannot replace in-person evaluation or the professional judgment of a qualified physician. If you have any further questions or if your symptoms worsen, please seek medical attention promptly.
Synovial haemangioma of the knee.
