MRI of diffuse-type tenosynovial giant cell tumour in the knee: a guide for diagnosis and treatment response assessment

Abstract

Tenosynovial giant cell tumour (TGCT) is a rare soft-tissue tumour originating from synovial lining of joints, bursae and tendon sheaths. The tumour comprises two subtypes: the localised-type (L-TGCT) is characterised by a single, well-defined lesion, whereas the diffuse-type (D-TGCT) consists of multiple lesions without clear margins. D-TGCT was previously known as pigmented villonodular synovitis. Although benign, TGCT can behave locally aggressive, especially the diffuse-type. Magnetic resonance imaging (MRI) is the modality of choice to diagnose TGCT and discriminate between subtypes. MRI can also provide a preoperative map before synovectomy, the mainstay of treatment. Finally, since the arrival of colony-stimulating factor 1-receptor inhibitors, a novel systemic therapy for D-TGCT patients with relapsed or inoperable disease, MRI is key in assessing treatment response. As recurrence after treatment of D-TGCT occurs more often than in L-TGCT, follow-up imaging plays an important role in D-TGCT. Reading follow-up MRIs of these diffuse synovial tumours may be a daunting task. Therefore, this educational review focuses on MRI findings in D-TGCT of the knee, which represents the most involved joint site (approximately 70% of patients). We aim to provide a systematic approach to assess the knee synovial recesses, highlight D-TGCT imaging findings, and combine these into a structured report. In addition, differential diagnoses mimicking D-TGCT, potential pitfalls and evaluation of tumour response following systemic therapies are discussed. Finally, we propose automated volumetric quantification of D-TGCT as the next step in quantitative treatment response assessment as an alternative to current radiological assessment criteria.

Keywords: 3D segmentation; Colony-stimulating factor 1; Diffuse-type TGCT; Magnetic resonance imaging; Tenosynovial giant cell tumour.

Fig. 1

Schematic overview of synovial recesses in the knee. a–d Sagittal drawings from lateral (a) to medial (d). e–h axial drawings from superior (e) to inferior (h)

Fig. 2

A case of D-TGCT demonstrating pre and post synovectomy findings on MRI. a Sagittal T2 weighted image shows multilobular posterior tumour with low signal intensity, and adjacent cyst-like components present within tumour in the popliteal cyst. Anterior, in the medial gutter of the suprapatellar recess smaller synovial proliferations are present. b Sagittal T1 SPIR post contrast performed 3 months after anterior and posterior synovectomy shows surgical clips with metal artefact anterior and posterior in the soft tissues, thickening of the quadriceps tendon, subcutaneous oedema and marked enhancement in Hoffa’s fatpad (asterisk) and along the posterior cortex of the tibia (subpopliteal recess). This mass-like enhancement can be post operative but residual tumour cannot be excluded at this time. MRI performed 3 years post synovectomy: c Sagittal T1 shows a bone erosion centrally in the tibial plateau (arrow). Furthermore, soft tissue masses posteriorly in the knee are present containing foci of low signal intensity. d Axial PD SPAIR shows a typical location of a lesion containing cystic components at the medial retrocondylar recess (arrow). e Sagittal T1 SPIR post contrast demonstrates enhancement of tumour within the tibia plateau erosion and of the posterior mass lesions. Note that Hoffa’s fat pad shows normalisation of fatty signal intensity except for a rim of tumour enhancement in the central synovial recess and inferior infrapatellar recess. f, g Time intensity curve of the tumour based on the region of interest (orange line) of the lesion demonstrated in d, showing early enhancement within 10 s after the artery (blue line) followed by a plateau phase (type III curve suggestive of a benign lesion)

Fig. 3

Blooming artefact. a Sagittal PD-weighted MR image of the knee in a patient with D-TGCT demonstrates multiple low signal intensity synovial lesions posterior to the PCL, along the posterior cortex of the femoral metaphysis and in the collapsed suprapatellar recess. b Sagittal T2- gradient echo weighted MR image of the knee showing blooming artefact: the low signal intensity synovial lesions containing hemosiderin increase in size and are ill defined, appearing as cloud-like dark areas. c Schematic illustration of hemosiderin signal intensities on gradient echo (GRE) weighted sequences versus T1- and T2-weighted sequences. Gradient echo images show increased size of the hemosiderin foci with irregular margins, this is called “blooming”

Fig. 4

Differential diagnosis: gout in the knee. a Lateral radiograph demonstrates marked pre-patellar soft tissue swelling containing increased density and several ill-defined calcifications (arrow). b Sagittal T1 shows a prepatellar, low signal intensity oval shaped soft tissue mass and a subchondral cyst in the patella. c Axial T2 FS confirms the prepatellar, low signal intensity mass invading the quadriceps tendon (arrows) and shows joint effusion containing multiple small synovial proliferations in the suprapatellar recess (asterisk). Aspiration of joint fluid with crystals confirmed the diagnosis of gout. d Axial T2 FS demonstrates low signal intensity soft tissue lesions in keeping with gout tophi deep to the collateral ligaments, causing erosion of the medial and lateral femoral condyles (arrows)

Fig. 5

Differential diagnosis: synovial chondromatosis in the knee. a Lateral radiograph illustrating multiple punctiform masses in the soft tissues of the knee containing speckled calcifications (arrows). These calcifications are present in Hoffa and posterior in the knee. b Sagittal T1 SPIR post contrast showing rim enhancement of the synovial lesions, which contain low signal intensity foci corresponding to the calcifications on X-ray. Only minimal joint effusion is present surrounding the cruciate ligaments with rim enhancement. c Axial T2 DIXON shows posterior extracapsular extension into the lateral head of gastrocnemius muscle (arrow)

Fig. 6

Differential diagnosis: lipoma arborescens. a Sagittal T1 demonstrates a hyperintense soft tissue mass in the suprapatellar recess, containing multiple villous proliferations (arrow). b Sagittal T1 SPIR post contrast shows the signal of the villi is suppressed and rim enhancement is present. In addition, there is mucoid degeneration of the anterior cruciate ligament and enhancing synovitis in the central synovial recess (arrowhead), superior and inferior infrapatellar recesses (asterisks), PCL and subpopliteal recess (arrows). c Axial T2 DIXON confirms fat suppression of the villi in the suprapatellar recess. These findings are in keeping with a lipoma arborescens, which is not a true neoplasm but rather a reactive process associated with rheumatoid or psoriatic arthritis or osteoarthritis

Fig. 7

MRI findings after treatment of D-TGCT with a CSF1R inhibitor. a Axial PD SPAIR images in a patient with intra-articular D-TGCT. Baseline image showing a target lesion (two axial diameters measured according to modified RECIST, dotted lines) in the medial suprapatellar recess. Note a smaller similar lesion in the lateral suprapatellar recess. b After 8 weeks on CSF1R-inhibitor therapy, the tumour showed a significant decrease in size and signal intensity. Joint effusion was resolved (not shown). The patient experienced improvement in symptoms of pain and swelling. c After 36 weeks, residual low signal intensity hemosiderin “scars” remained both in the medial and lateral suprapatellar recesses

Fig. 8

Volumetric segmentations of D-TGCT performed with Brainlab software on sagittal T1 SPIR-weighted sequences post gadolinium. a Tumour is segmented in the PCL recess (volume shown in red). Volume: 3.8 cm³. b Tumour segmentation in anterior, middle and posterior compartments. Volume: 86.2 cm³. c Tumour segmentation of a case with marked posterior disease, present in the PCL recess, subgastrocnemius synovial recesses, Baker’s cyst, and extending extra-articular in the popliteal fossa. Volume: 91.9 cm³