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Tenosynovial giant cell tumor-diffuse type (diffuse TSGCT) is a benign but locally aggressive proliferative disorder of the synovium. Treatment is usually surgical, although in cases of extensive disease complete synovectomy is not possible and local recurrence rates are high. Pexidartinib (trade name Turalio®), a colony-stimulating factor-1 (CSF-1) inhibitor, was shown in a recent phase III trial to effectively treat diffuse TSGCT and is FDA approved for the treatment of adult patients with symptomatic diffuse TSGCT associated with severe morbidity or functional limitations and not amenable to improvement with surgery. Pexidartinib is available only through a restricted program under a risk evaluation and mitigation strategy (REMS) because of the risk of hepatotoxicity. Magnetic resonance imaging (MRI) is the preferred imaging modality for the diagnosis and surveillance of TSGCT. Here we present three patients with diffuse TSGCT of the knee who underwent multiple MRIs over several years while on pexidartinib. We describe the disease burden and signal characteristics on MRI and correlate with the response reported in the patients' medical records. Given that the use of pexidartinib and other CSF inhibitors is likely to increase, musculoskeletal radiologists should be aware of this novel non-operative treatment and the MRI appearance of diffuse TSGCT during therapy.

A tenosynovial giant cell tumor is a benign proliferative disease, mostly arising from the synovial membrane of tendon sheaths, bursae, and joints. Axial skeleton involvement is very rare, but it is often found in the cervical spine. Spinal tenosynovial giant cell tumors often arise at the facet joints; a completely extra-articular spinal tenosynovial giant cell tumor is rare. We report an extremely rare case of tenosynovial giant cell tumor in the upper cervical spine that extended from the posterior atlanto-occipital membrane rather than the facet joint. Herein, the clinical and radiological findings will be reviewed to better our understanding of the characteristics of spinal tenosynovial giant cell tumors, and to help improve their diagnosis despite their non-typical locations of origin.

We report on a 40-year-old male with a 9-month-long history of snapping of his right hip caused by a previously undescribed etiology of internal extra-articular snapping hip, namely due to a localized tenosynovial giant cell tumor. Both dynamic ultrasound evaluation and MRI proved to be crucial in the diagnosis of this rare entity. Auto-provocation of the snapping showed an anterior hip mass moving posteriorly to the psoas tendon which elucidated the pain and clicking sensation. Subsequent MRI demonstrated a peripheral low-intensity rim due to hemosiderin deposition around the synovial mass which is indicative for pigmented villonodular tenosynovitis. Treatment consisted of arthroscopic shaver burr resection. Immediately postoperatively, the snapping sensation could not be provoked anymore by the patient. The purpose of reporting on this case report is to emphasize several successive learning points. First, dynamic ultrasound aids in diagnosis and differentiation of the types of snapping hip. Second, specific MRI features are suggestive of tenosynovial giant cell tumor, recognizing these traits may prevent delayed diagnosis and subsequent aggravated clinical course. Third, localized pigmented villonodular tenosynovitis around the hip may present as an internal extra-articular snapping hip and is of consideration in the differential diagnosis of recurrent snapping hip.

To determine the frequency with which MRI of tenosynovial giant cell tumor demonstrates hemosiderin, visible intralesional fat signal, and proximity to synovial tissue.This is a retrospective study of 31 cases of tenosynovial giant cell tumors which had concomitant MRI. Images were examined for lesion size, morphology, origin, bone erosions, MRI signal characteristics, contrast enhancement, and blooming artifact, comparing prospective and retrospective reports. Histology was reviewed for the presence of hemosiderin and xanthoma cells.Eight lesions were diffuse and 23 were localized nodules. Three lesions were located in subcutaneous tissue and 4 adjacent to tendons beyond the extent of their tendon sheath. All lesions exhibited areas of low T1- and T2-weighted signal. Blooming artifact on gradient echo imaging was present in 86% of diffuse and only 27% of nodular disease. There was interobserver variability of 40% in assessing blooming. Iron was visible on HE or iron stain in 97% of cases. Fat signal intensity was seen in only 3% of cases, although xanthoma cells were present on in 48%. The correct diagnosis was included in the prospective radiology differential diagnosis in 86% of diffuse cases and 62% of nodular cases.Blooming on GRE MRI has low sensitivity for nodular tenosynovial giant cell tumors and is not universal in diffuse tumors. There was high interobserver variability in assessment of blooming. Intralesional fat signal is not a useful sign and may occur adjacent to tendons which lack a tendon sheath and may occur in a subcutaneous location.

Tenosynovial giant cell tumor (TGCT) is a benign condition that arises from tendon sheaths, synovium, or bursae and is classified according to the site of involvement (intra-articular versus extra-articular) and pattern of growth (localized versus diffuse). The diffuse form tends to present as peri-articular masses and are locally aggressive. It usually presents as a mono-articular process affecting larger joints. Spinal involvement is extremely rare, particularly the cervical spine. In this case report, we present a pediatric case of spinal TGCT involving the C1-C2 joint which was incidentally detected in a 13-year-old girl undergoing surveillance for medulloblastoma recurrence. Although spinal TGCT is a benign condition, it remains a diagnostic challenge, which specific to our case can raise the concern for malignancy or metastasis. We also described a percutaneous biopsy approach using a spring-loaded blunt tip coaxial needle to avoid inadvertent vascular injury. The imaging features of spinal TGCT and biopsy approach for atlantoaxial lesion are discussed together with a comprehensive review of the literature.

Diffuse-type tenosynovial giant cell tumor (TSGCT) is a rare, locally aggressive neoplasm. It most commonly occurs in the knee, followed by the hip, and has distinctive imaging features, including mass-like foci of low T2 signal intensity, "blooming" on gradient-echo MRI, and pronounced uptake on FDG PET/CT. Histologically, TSGCT demonstrates a neoplastic population of mononuclear cells admixed with hemosiderin-laden macrophages, foamy histiocytes, inflammatory cells, and osteoclast-like giant cells. In cases where diffuse-type TSGCT presents in an uncommon location or with atypical features, the imaging diagnosis may be challenging. Furthermore, because of its polymorphous appearance, it may be mistaken microscopically for other neoplastic and non-neoplastic histiocytic lesions. Herein, we present two cases of diffuse-type TSGCT presenting as large masses, and underscore the importance of radiologic-pathologic correlation for accurate diagnosis.

Desmoplastic fibroblastoma is an uncommon, benign fibrous soft tissue tumor that usually occurs in the arms, shoulders, neck, hands, and feet in the fifth to seventh decades of life. In general, it is commonly located in the subcutaneous tissue and skeletal muscle. The authors report an unusual case of a desmoplastic fibroblastoma mimicking tenosynovial giant cell tumor encasing a tendon of the foot in a 72-year-old woman. Ultrasonography revealed an inhomogeneously hypoechoic lobulated soft tissue lesion completely wrapped around the extensor digitorum longus tendon. Color Doppler study revealed increased vascularity in the internal and peripheral portions of the lesion. Magnetic resonance imaging revealed a well-defined, lobulated soft tissue mass encasing the extensor digitorum longus tendon with predominantly isointense signal with some areas of hypointense signal on T1-weighted images, predominantly hyperintense signal with some areas of hypointense signal on T2-weighted images, and inhomogeneous enhancement on fat-suppressed contrast-enhanced T1-weighted images. Surgical excision was performed, and the mass was diagnosed on pathological examination as a desmoplastic fibroblastoma. There has been no previously published radiologic case of a desmoplastic fibroblastoma encasing a tendon of the foot in the literature.

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms composed of perivascular epithelioid cells that are immunoreactive for both melanocytic and myogenic markers. Recently, a fibroma-like PEComa associated with tuberous sclerosis complex (TSC) has been identified. We describe the first intra-articular case of a fibroma-like PEComa in a 44-year-old man who presented with a hypointense intra-articular knee mass, which was mistaken for tenosynovial giant cell tumor, diffuse type. This case report demonstrates that fibroma-like PEComa should be included in the extended differential diagnosis of intra-articular soft tissue masses. In addition, given their strong association with TSC mutations, a diagnosis of fibroma-like PEComa should trigger an evaluation for TSC.

In 2013, the WHO revised the terminology for the family of lesions previously described as giant cell tumor of the tendon sheath and pigmented villonodular synovitis. The correct current terminology is tenosynovial giant cell tumors, further subclassified by the extent (localized or diffuse) and location (intraor extraarticular) [1]. Intraarticular lesions are usually monoarticular and usually affect the knee [2]. The localized intraarticular lesion was formerly termed as localized pigmented villonodular synovitis. The diffuse intraarticular diffuse type affects the entire joint synovium, and patients typically present with a long history of pain, swelling, restricted movement and occasional hemarthrosis [2, 3]. Localized intraarticular tenosynovial giant cell tumor is characterized by limited involvement of the synovium presenting as an intraarticular nodule or mass, which can result in mechanical symptoms, including locking, as presented in our case [2, 4]. Localized intraarticular tenosynovial giant cell tumor of the knee is usually located in the meniscocapsular junction, anterior tibial eminence, intercondylar notch region or lateral recesses. It is rarely located in the fat pad, medial femoral condyle, mediopatellar synovial plica or inside a popliteal cyst [2, 3]. Infrequently, the pedicle can be subject to torsion, resulting in tumor infarction [2]. Our patient suffered from sudden knee pain with movement limitation. A radiograph revealed a persistent secondary ossification center of the tibial tuberosity; however, this was considered irrelevant to his clinical symptoms (Fig. 1 testyourself question). An immediate MR imaging examination confirmed a nodular lesion in the anterior aspect of the femorotibial joint, which was predominantly hypointensive on PD and PD fat-suppressed images, with profoundly hypointensive signal on GRE images (Fig. 2 test-yourself question), consistent with a hemosiderin-laden lesion [4–6]. Additional MR imaging sequences were performed the following morning after resolution of the patient’s symptoms, presumed to be due to spontaneous relocation of the nodule, for further lesion characterization and included T1W, T2W and enhanced fat-suppressed T1W images (Fig. 3 testyourself question). Decreased signal intensity was again seen with a prominent peripheral rind of enhancement and mild inner enhancement [2, 4, 5, 7]. The diagnosis of intraarticular localized tenosynovial giant cell tumor was suggested, and the mass was subsequently removed arthroscopically [2, 3, 7]. Arthroscopy confirmed a pedunculated lesion arising beneath the synovial surface with histology demonstrating synoviallike mononuclear cells, scattered osteoclast-like cells, siderophages and areas of hemosiderin deposition (Fig. 4 test-yourself question). As described, localized intraarticular tenosynovial giant cell tumor can present with transient knee locking, which typically suggests a differential diagnosis that includes meniscal lesions, chondral lesions and loose bodies [2, 7]. MR imaging was indispensable in this case, showing a hemosiderin-laden nodule in Hoffa’s fat. Localized intraarticular lesions such as synovial hemangioma, synovial lipoma, ganglion, a multifocal synovial chondromatosis or primary intraarticular The case presentation can be found at doi:10.1007/s00256-015-2287-1.