Recurrent diffuse tenosynovial giant cell tumor of the posterior knee: a rare presentation with synovial herniation (Baker’s cyst) in a young patient

Abstract

Introduction

Tenosynovial giant cell tumor (TGCT), previously referred to as pigmented villonodular synovitis (PVNS), is a rare, locally aggressive proliferative disorder of the synovium. It typically affects large joints, most commonly the knee. Posterior compartment involvement in the knee is less common compared to anterior or suprapatellar involvement, and it presents unique diagnostic and therapeutic challenges due to the complex anatomy and proximity to neurovascular structures. While popliteal (Baker’s) cysts may coexist with intra-articular TGCT, they are considered synovial herniation cysts rather than true extra-articular involvement, which can be associated with diagnostic and therapeutic challenges.

Case Presentation

This case report describes a 24-year-old male with recurrent diffuse TGCT of the knee, predominantly involving the posterior compartment, along with a large Baker’s cyst and synovial thickening adjacent to the medial femoral condyle. Magnetic resonance imaging (MRI) revealed extensive synovial proliferation with characteristic low T2 signal intensity, confirming the diagnosis and guiding surgical planning. The patient underwent arthroscopic-assisted synovectomy to address both the suprapatellar and posterior compartments while preserving critical neurovascular structures. Postoperatively, the patient had improved knee function and was referred for adjuvant therapy to minimize recurrence risk.

Conclusion

This case highlights the importance of accurate imaging, meticulous surgical planning, and a multidisciplinary approach in managing rare presentations of TGCT. Long-term follow-up and consideration of adjuvant therapies such as radiotherapy or systemic therapies, including Pexidartinib, remain essential to minimize recurrence and optimize outcomes.

Introduction

Tenosynovial giant cell tumor (TGCT), formerly known as pigmented villonodular synovitis (PVNS), is a rare, benign but locally aggressive proliferative disorder of the synovium, typically affecting large joints, most commonly the knee [1, 2]. TGCT is characterized by hemosiderin deposition, multinucleated giant cells, and chronic synovial inflammation, which can lead to progressive joint damage if untreated [3]. The condition predominantly involves intra-articular synovium, including the anterior and suprapatellar regions, which are rich in synovial tissue [4]. In contrast, posterior compartment involvement is common in diffuse TGCT due to its intra-articular nature. However, cases with predominant involvement of the posterior compartment, as seen in this report, are less frequently discussed in the literature and pose unique diagnostic and management challenges due to the region’s anatomical complexity [5, 6]. Posterior compartment involvement of TGCT is often misdiagnosed as other posterior knee pathologies, including Baker’s cysts, soft tissue tumors, or popliteal tendinopathy [7]. Baker’s cysts, commonly referred to as popliteal cysts, are synovial herniation cysts caused by increased intra-articular pressure and are frequently associated with intra-articular pathologies such as TGCT [8]. However, they do not represent true extra-articular involvement of TGCT, which would require direct synovial tumor extension into surrounding tissues outside the joint capsule [6, 9]. This report describes a rare case of diffuse TGCT with predominant posterior compartment involvement, a large Baker’s cyst, and synovial thickening in the popliteal tendon sheath and medial femoral condyle. While TGCT is a well-documented entity, its posterior localization is noteworthy due to its associated diagnostic and therapeutic challenges. This case highlights the importance of MRI and precise surgical planning in managing TGCT in this anatomically complex region.

Case presentation

A 24-year-old male presented with recurrent pain and swelling in the right knee. He was initially diagnosed with tenosynovial giant cell tumor (TGCT), previously referred to as pigmented villonodular synovitis (PVNS), in 2019 and underwent an open posterior synovectomy at that time. A recurrence occurred in 2021, which was treated with arthroscopic synovectomy. By 2024, the patient reported persistent knee effusion and pain, limiting his daily activities despite prior interventions. On physical examination, there was mild swelling and tenderness over the suprapatellar region, with a restricted range of motion. Ligamentous stability and neurovascular status were intact. Magnetic resonance imaging (MRI) revealed diffuse synovial thickening with nodular features and characteristic low T2 signal intensity, consistent with diffuse TGCT. The imaging demonstrated a large multilobulated Baker’s cyst measuring 3.8 × 10 cm, located posteriorly, consistent with a synovial herniation cyst secondary to intra-articular TGCT [Fig. 1]. Additionally, MRI revealed synovial thickening adjacent to the medial femoral condyle, with no evidence of direct extra-articular tumor extension [Fig. 2]. Also, there were cartilage changes in the tibial plateau with minimal focal myxoid degeneration and evidence of small partial-thickness cartilage loss [Fig. 2]. Axial imaging confirmed the size and extent of the Baker’s cyst [Fig. 3]. The findings were significant for disease complexity, particularly involving the posterior compartment. The patient underwent arthroscopic-assisted synovectomy under spinal anesthesia. Diagnostic arthroscopy revealed inflamed synovium with cartilage changes in the patella, medial, and lateral compartments. Posteromedial and posterolateral portals were utilized to access the posterior compartment, allowing for thorough visualization and synovectomy. Synovectomy was performed in a systematic, stepwise manner, starting in safer peripheral regions and working toward critical areas to minimize the risk of iatrogenic injury, with careful protection of the neurovascular bundle. This was achieved by maintaining a clear surgical plane, using blunt-tipped instruments, and avoiding excessive dissection near neurovascular structures. The Baker’s cyst, identified as a secondary synovial herniation, was excised by removing its wall and contents to minimize recurrence risk. Postoperatively, the patient started physical therapy to regain knee range of motion. During the two-week follow-up, the patient reported mild residual effusion but was progressing well with rehabilitation. The surgical wound was healing satisfactorily, and there were no signs of infection or complications. Given the diffuse nature of TGCT and the high recurrence rates associated with the condition, the patient was referred to oncology for evaluation. The decision for adjuvant therapy, including radiotherapy or systemic treatment with Pexidartinib, was deferred to the oncology team in consultation with the patient. The options discussed included radiotherapy or systemic treatment with Pexidartinib, a colony-stimulating factor 1 receptor (CSF1R) inhibitor, both of which have shown efficacy in reducing recurrence risk. Ultimately, the choice of adjuvant treatment was left to be further evaluated by oncology during follow-up visits.

Fig. 1

Sagittal T2-weighted MRI scan of the knee demonstrating diffuse synovial thickening in the posterior compartment and a large multilobulated Baker's cyst (synovial herniation cyst) indicated by the white arrow

Fig. 2

Coronal T1-weighted MRI scan of the knee joint using a 3D LAVA Flex sequence with contrast (In Phase) demonstrating synovial thickening indicated by the black arrow

Fig. 3

Axial T1-weighted MRI scan of the knee using a 3D LAVA Flex sequence with contrast (Out Phase) demonstrating popliteal (Baker) cyst indicated by the white arrow

Discussion

Tenosynovial giant cell tumor (TGCT) is a rare, locally aggressive synovial proliferative disorder with an estimated incidence of 1.8 cases per million per year [1]. Diffuse TGCT often leads to extensive joint involvement, pain, and recurrent effusion. This case is noteworthy due to the predominant involvement of the posterior compartment and associated features, including a large Baker’s cyst and synovial thickening adjacent to the medial femoral condyle. The Baker’s cyst in this context represents a synovial herniation cyst caused by increased intra-articular pressure secondary to TGCT, rather than true extra-articular involvement [6, 8]. Synovial thickening adjacent to the medial femoral condyle, as seen on imaging, does not represent extra-articular tumor extension but rather localized synovial involvement. MRI remains the gold standard for diagnosing TGCT and assessing disease extent. The low T2 signal intensity seen on MRI is characteristic due to hemosiderin deposition [8]. In this case, MRI confirmed the diagnosis and guided surgical planning, particularly in addressing the posterior compartment and adjacent structures. Surgical management of diffuse TGCT, particularly in the posterior compartment, requires meticulous planning due to the proximity of critical neurovascular structures. Posteromedial and posterolateral portals provide safe and effective access to the posterior compartment, and anatomical landmarks such as the gastrocnemius heads should guide their placement [9, 10]. Intraoperative visualization can be enhanced using continuous irrigation and a 30-degree arthroscope, particularly for hard-to-reach areas [8]. Blunt-tipped instruments, such as synovial shavers and graspers, should be used to minimize the risk of iatrogenic injury [6]. A layer-by-layer approach to dissection, starting from peripheral regions and progressing toward critical areas, is recommended to preserve the neurovascular bundle [10]. For Baker’s cysts associated with TGCT, complete excision of the cyst wall and its content is critical to prevent recurrence [6]. Postoperative care, including early mobilization and physical therapy, plays a crucial role in optimizing recovery and minimizing complications [10, 11]. Despite optimal surgical management, recurrence rates for diffuse TGCT remain high, ranging from 8 to 56% [10]. Adjuvant therapies, including radiotherapy (e.g., intra-articular yttrium-90 or external beam radiation), have shown efficacy in reducing recurrence rates [11]. Recently, systemic therapies such as Pexidartinib, a colony-stimulating factor 1 receptor (CSF1R) inhibitor, have demonstrated promising results in managing refractory TGCT [12]. This case underscores the importance of a multidisciplinary approach, including orthopedic surgeons, radiologists, and oncologists, to optimize outcomes. Advanced imaging and surgical planning are critical for managing TGCT. Long-term follow-up is essential to detect recurrence early and implement additional therapies as needed.

Conclusion

This case highlights the rarity of diffuse TGCT with extensive intra-articular involvement in a young patient, emphasizing the importance of considering TGCT in the differential diagnosis of posterior knee pathologies, especially when associated with Baker’s cysts. The coexisting Baker’s cyst represents a synovial herniation cyst secondary to TGCT, rather than true extra-articular tumor extension. Early diagnosis, accurate imaging, and meticulous surgical planning are essential for optimal management. Arthroscopic synovectomy provides a minimally invasive approach to symptom relief, though the high recurrence rate of TGCT necessitates long-term follow-up and consideration of adjuvant therapies such as radiotherapy or systemic treatments like Pexidartinib. Multidisciplinary collaboration remains crucial in managing this challenging condition and improving patient outcomes.