Rhabdomyosarcoma Arising in Inflammatory Rhabdomyoblastic Tumor: A Genetically Distinctive Subtype of Rhabdomyosarcoma.

"Inflammatory rhabdomyoblastic tumor" (IRMT) is a recently coined name for a distinctive soft tissue neoplasm characterized by slow growth, a dense histiocytic infiltrate, scattered, bizarre-appearing tumor cells with morphologic and immunohistochemical evidence of skeletal muscle differentiation, a near-haploid karyotype with retained biparental disomy of chromosomes 5 and 22, and usually indolent behavior. There are 2 reports of rhabdomyosarcoma (RMS) arising in IRMT. We studied the clinicopathologic and cytogenomic features of 6 cases of IRMT with progression to RMS. Tumors occurred in the extremities of 5 men and 1 woman (median patient age, 50 years; median tumor size, 6.5 cm). Clinical follow-up (6 patients: median, 11 months; range 4-163 months) documented local recurrence and distant metastases in 1 and 5 of 6 patients, respectively. Therapy included complete surgical resection (4 patients) and adjuvant/neoadjuvant chemo/radiotherapy (6 patients). One patient died of disease, 4 were alive with metastatic disease, and one was without evidence of disease. All primary tumors contained conventional IRMT. Progression to RMS appeared as follows: (1) overgrowth of monomorphic rhabdomyoblasts with diminished histiocytes, (2) monomorphic spindle cell morphology with variably pleomorphic rhabdomyoblasts and low mitotic activity, or (3) morphologically undifferentiated spindle cell and epithelioid sarcoma. All but one were diffusely desmin-positive, with more limited MyoD1/myogenin expression. All RMS arising in IRMT, either primary or metastatic, demonstrated widespread loss of heterozygosity with retained heterozygosity of chromosomes 5 and 20, and all but one displayed additional gains and losses involving loci containing oncogenes/ tumor suppressor genes, most often CDKN2A and CDKN2B. RMS arising in IRMT have unique clinicopathologic and cytogenomic features, warranting classification as a distinct, potentially aggressive RMS subtype. It should be distinguished from other RMSs, particularly fusion-driven spindle cell RMS and pleomorphic RMS.

Fusion-driven Spindle Cell Rhabdomyosarcomas of Bone and Soft Tissue: A Clinicopathologic and Molecular Genetic Study of 25 Cases.

The evolving classification of rhabdomyosarcoma (RMS) now includes spindle cell RMS (SRMS). Bone/soft tissue SRMS often harbor TFCP2, or less often MEIS1 rearrangements. We studied 25 fusion-driven SRMS involving bone (n = 19) and soft tissue (n = 6). Osseous SRMS occurred in 13 women and 6 men (median age: 41 years) and involved the pelvis (5), sacrum (2), spine (4), maxilla (4), mandible (1), skull (1), and femur (2). Follow-up (median: 5 months) demonstrated local recurrence in 2/16 and distant metastases in 8/17 patients (median time to metastasis: 1 month). Eight patients died of disease; 9 were alive with disease. Soft tissue SRMS occurred in 4 men and 2 women (median: 50 years). Follow-up (median: 10 months) revealed distant metastasis at diagnosis (1), alive with unresected tumor (1), and no evidence of disease (4). Next-generation sequencing demonstrated FUS::TFCP2 (12), EWSR1::TFCP2 (3) and MEIS1::NCOA2 (2); FISH identified EWSR1 (2) rearrangements. Most TFCP2-rearranged SRMS (13/17) showed spindled/epithelioid morphology, rarely with rhabdomyoblasts. The bone tumors were diffusely desmin and MyoD1 positive with limited myogenin; 10/13 were ALK -positive and 6/15 were keratin positive. Soft tissue SRMS harbored EWSR1::TFCP2, MEIS1::NCOA2, ZFP64::NCOA2, MEIS1::FOXO1, TCF12::VGLL3 and DCTN1::ALK, and displayed spindled/epithelioid, leiomyomatous, and myxofibrosarcoma-like morphologies. Immunohistochemistry (IHC) was positive for MyoD1 (6/6), focal desmin (5/6), myogenin (3/6), and keratin (1/6). We conclude that TFCP2-rearranged SRMS of bone and soft tissue show consistent morphologic and IHC features, likely representing a distinct subset of RMS. Non-TFCP2 fusion-positive SRMS could represent a single RMS subset, multiple subtypes of RMS, or "fusion-defined" sarcomas with rhabdomyoblastic differentiation.

Multimodality imaging features of USP6-associated neoplasms.

Since the discovery of USP6 gene rearrangements in aneurysmal bone cysts nearly 20 years ago, we have come to recognize that there is a family of USP6-driven mesenchymal neoplasms with overlapping clinical, morphologic, and imaging features. This family of neoplasms now includes myositis ossificans, aneurysmal bone cyst, nodular fasciitis, fibroma of tendon sheath, fibro-osseous pseudotumor of digits, and their associated variants. While generally benign and in many cases self-limiting, these lesions may undergo rapid growth, and be confused with malignant bone and soft tissue lesions, both clinically and on imaging. The purpose of this article is to review the imaging characteristics of the spectrum of USP6-driven neoplasms, highlight key features that allow distinction from malignant bone or soft tissue lesions, and discuss the role of imaging and molecular analysis in diagnosis.

Multimodality imaging features of parosteal lipomas.

OBJECTIVE: To examine the multimodality imaging characteristics of parosteal lipomas. MATERIALS AND METHODS: With IRB approval, our institutional imaging database and medical record were retrospectively reviewed from 1990-2020 for cases of pathologically-proven and/or imaging diagnosed parosteal lipomas. RESULTS: There were 22 patients (12 males, 10 females) with a mean age of 57.1 ± 12.7 years (range 31-80 years). 11/22 cases (50%) were pathologically-confirmed on biopsy or surgical resection and 11/22 (50%) had imaging features compatible with parosteal lipoma. Lesions occurred most commonly along the femur (8/22, 36%), followed by the forearm (3/22, 14%). All cases demonstrated a juxtacortical fatty mass containing an osseous excrescence that was firmly attached to the cortical surface. The osseous excrescences were characterized as pedunculated in 16/22 (73%) and sessile in 6/22 (27%). The average largest dimension of the osseus excrescences was 2.4 ± 1.6 cm (range 0.8-6.1 cm) and the lipomatous portions 7.8 ± 3.8 cm (range 2.0-19.5 cm). The excrescences contained mature bone in 12/22 (55%) cases and a mixture of mature bone and radiating bone spicules in 10/22 (45%). There were non-lipomatous elements in the fatty portion of the mass in 13/22 (59%) of cases. Most cases (19/22, 85%) had cortical thickening/periostitis near the base of the osseous stalk. Two patients had a bone scan that demonstrated uptake in the osseous excrescence, and two patients had an FDG PET/CT that demonstrated no uptake. CONCLUSION: Parosteal lipomas are a rare benign lipomatous tumor with pathognomonic multimodality imaging features that may obviate the need for biopsy.

PET imaging characteristics of neuromuscular choristoma and associated desmoid-type fibromatosis.

BACKGROUND: Neuromuscular choristoma (NMC) is a rare peripheral nerve lesion characterized by abnormal presence of muscle within nerve. Associated desmoid-type fibromatosis (NMC-DTF) often develops. We report 18F-fluorodeoxyglucose positron emission tomography (FDG PET) characteristics of NMC and NMC-DTF and propose that increased FDG activity within NMCs may be associated with subclinical NMC-DTF or NMC-DTF "precursor" tissue. METHODS: Our institutional database was searched for all NMC cases. Inclusion criteria were 1) confirmed diagnosis of NMC with or without biopsy, and 2) available PET and MRI studies. PET data included SUVmax and SUVmean of NMCs, contralateral limb normal skeletal muscle and unaffected nerves, and SUVmax of NMC-DTF if present. SUV values were compared using paired t-test. A p value of < 0.05 was considered statistically significant. RESULTS: Our cohort consisted of 9 patients with NMC, 8 cases involving sciatic nerve and 1 of brachial plexus. On PET imaging, all NMC-affected nerve segments showed significantly higher FDG uptake (SUVmax/mean) compared to both contralateral normal nerve and normal skeletal muscle (all P < 0.05). Similar to sporadic DTF, NMC-DTF was highly FDG-avid (average SUVmax of 4.2). SUVmax in NMC with or without concurrent NMC-DTF did not differ (p = 0.76). Within NMC-affected nerve segment, FDG activity was relatively higher in areas with low T1/T2 MR signal. CONCLUSION: All NMCs were more FDG avid compared to both normal skeletal muscle and contralateral unaffected nerve, arguing against the presence of heterotopic muscle in NMC as the source of FDG avidity. FDG avidity within NMC may reflect subclinical NMC-DTF or a precursor lesion, as NMC-DTF are highly FDG-avid, and the highest regions of FDG avidity in NMC occurred in regions with MR characteristics associated with NMC-DTF (i.e., lower T1/T2 signal). We believe that the integration of FDG PET with serial MR imaging in patient follow up will clarify its utility in both detection and surveillance of NMC-DTF.

Novel imaging techniques using 18 F-florbetapir PET/MRI can guide fascicular nerve biopsy in amyloid multiple mononeuropathy.

BACKGROUND: Multiple mononeuropathy is a rare presentation of primary (AL) amyloidosis and nerve biopsy is usually needed for diagnosis. Conventional imaging is useful to identify proximal nerve involvement but may be inadequate. We report a patient with multiple mononeuropathy whose presentation was suggestive of AL amyloid neuropathy and in whom repeated tissue biopsies were negative for amyloid (including two sensory nerves and one muscle). METHODS: The patient underwent magnetic resonance imaging (MRI) and whole body 18 F-florbetapir positron emission tomography (PET)/MRI. RESULTS: Whole body 18 F-florbetapir PET/MRI revealed abnormal low-level florbetapir uptake in the right proximal tibial and peroneal nerves, which provided a target for a sciatic bifurcation fascicular nerve biopsy that was diagnostic of AL amyloidosis. CONCLUSIONS: 18 F-florbetapir PET/MRI imaging is a promising diagnostic tool for patients with suspected peripheral nerve amyloidosis (including multiple mononeuropathy) in whom conventional imaging and nerve and muscle biopsies miss the pathology.

Frequency and Characteristics of Nodal and Deltoid FDG and 11C-Choline Uptake on PET Performed After COVID-19 Vaccination.

BACKGROUND. COVID-19 vaccination may trigger reactive lymphadenopathy, confounding imaging interpretation. There has been limited systematic analysis of PET findings after COVID-19 vaccination. OBJECTIVE. The purpose of this study was to evaluate the frequency and characteristics of abnormal FDG and 11C-choline uptake on PET performed after COVID-19 vaccination. METHODS. This retrospective study included 67 patients (43 men and 24 women; mean [± SD] age, 75.6 ± 9.2 years) who underwent PET examination between December 14, 2020, and March 10, 2021, after COVID-19 vaccination and who had undergone prevaccination PET examination without visible axillary node uptake. A total of 52 patients received the BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech; hereafter referred to as the Pfizer-BioNTech vaccine), and 15 received the SARS-CoV-2 mRNA-1273 vaccine (Moderna; hereafter referred to as the Moderna vaccine). Sixty-six of the patients underwent PET/CT, and one underwent PET/MRI. Fifty-four PET examinations used FDG, and 13 used 11C-choline. PET was performed a median of 13 and 10 days after vaccination for patients who had received one (n = 44) and two (n = 23) vaccine doses, respectively. Two nuclear medicine physicians independently reviewed images and were blinded to injection laterality and the number of days since vaccination. Lymph node or deltoid SUVmax greater than the blood pool SUVmax was considered positive. Interreader agreement was assessed, and the measurements made by the more experienced physician were used for subsequent analysis. RESULTS. Positive axillary lymph node uptake was observed in 10.4% (7/67) of patients (7.4% [4/54] of FDG examinations and 23.1% [3/13] of 11C-choline examinations); of the patients with positive axillary lymph nodes, four had received the Pfizer vaccine, and three had received the Moderna vaccine. Injection laterality was documented for five of seven patients with positive axillary lymph nodes and was ipsilateral to the positive node in all five patients. PET was performed within 24 days of vaccination for all patients with a positive node. One patient showed extraaxillary lymph node uptake (ipsilateral supraclavicular uptake on FDG PET). Ipsilateral deltoid uptake was present in 14.5% (8/55) of patients with documented injection laterality, including 42.9% (3/7) of patients with positive axillary lymph nodes. Interreader agreement for SUV measurements (expressed as intraclass correlation coefficients) ranged from 0.600 to 0.988. CONCLUSION. Increased axillary lymph node or ipsilateral deltoid uptake is occasionally observed on FDG or 11C-choline PET performed after COVID-19 vaccination with the Pfizer-BioNTech or Moderna vaccine. CLINICAL IMPACT. Interpreting physicians should recognize characteristics of abnormal uptake on PET after COVID-19 vaccination to guide optimal follow-up management and reduce unnecessary biopsies.

Chordoma: 18F-FDG PET/CT and MRI imaging features.

OBJECTIVE: Examine the 18F-FDG PET/CT and MRI imaging characteristics of chordoma. MATERIALS AND METHODS: Biopsy-proven chordoma with a pre-therapy 18F-FDG PET/CT from 2001 through 2019 in patients > 18 years old were retrospectively reviewed. Multiple PET/CT and MRI imaging parameters were assessed. RESULTS: A total of 23 chordoma patients were included (16 M, 7 F; average age of 60.1 ± 13.0 years) with comparative MRI available in 22 cases. This included 13 sacrococcygeal, 9 mobile spine, and one clival lesions. On 18F-FDG PET/CT, chordomas demonstrated an average SUVmax of 5.8 ± 3.7, average metabolic tumor volume (MTV) of 160.2 ± 263.8 cm3, and average total lesion glycolysis (TLG) of 542.6 ± 1210 g. All demonstrated heterogeneous FDG activity. On MRI, chordomas were predominantly T2 hyperintense (22/22) and T1 isointense (18/22), contained small foci of T1 hyperintensity (17/22), and demonstrated heterogeneous enhancement (14/20). There were no statistically significant associations found between 18F-FDG PET/CT and MRI imaging features. There was no relationship of SUVmax (p = 0.53), MTV (p = 0.47), TLG (p = 0.48), maximal dimension (p = 0.92), or volume (p = 0.45) to the development of recurrent or metastatic disease which occurred in 6/22 patients over a mean follow-up duration of 4.1 ± 2.0 years. CONCLUSION: On 18F-FDG PET/CT imaging, chordomas demonstrate moderate, heterogeneous FDG uptake. Predominant T2 hyperintensity and small foci of internal increased T1 signal are common on MRI. The inherent FDG avidity of chordomas suggests that 18F-FDG PET/CT may be a useful modality for staging, evaluating treatment response, and assessing for recurrent or metastatic disease.

BRAF inhibitor-induced panniculitis in patients treated for stage IV metastatic melanoma: a case series.

BRAF and MEK inhibitor combination therapy is the standard treatment for patients with BRAF V600E mutant metastatic melanoma. Neutrophilic panniculitis is a known rare complication of BRAF inhibitor therapy and can act as a potential mimic of melanoma metastases on 18F-FDG PET/CT. In this case series, we present three cases of BRAF inhibitor-induced panniculitis in patients being treated for BRAF-mutant metastatic melanoma and emphasize the use of ultrasound to differentiate between panniculitis lesions, which are typically ill-defined echogenic masses and subcutaneous soft tissue melanoma metastases, which present as hypoechoic vascular masses.

Fluorodeoxyglucose-Positron Emission Tomography Predicts Bone Marrow Involvement in the Staging of Follicular Lymphoma.

BACKGROUND: Standard bone marrow biopsy (BMB) and bone involvement with follicular lymphoma (FL) on positron emission tomography (PET)/computed tomography (CT) both predict early clinical failure in FL. The key clinical question is whether PET/CT findings can obviate the need for BMB. The goal of this study was to determine the value of PET/CT in determining bone involvement in FL, using posterior iliac crest BMB as the gold standard. MATERIALS AND METHODS: A total of 548 patients with newly diagnosed grade 1-3A FL were included. The presence, pattern, and location of bone involvement, spleen involvement, and standardized uptake values (SUVs) in the L3 vertebral body were recorded for all patients and compared with the BMB report. RESULTS: Excluding patients with focal bone lesions on PET/CT, the sensitivity and specificity of PET/CT in detecting bone or marrow involvement, compared with BMB, were 53% and 88%, respectively. The sensitivity and specificity of spleen involvement on PET/CT in predicting a positive BMB were 55% and 86%, respectively. An L3 SUVmax of less than 2.0 resulted in a negative predictive value (NPV) of 96% for marrow involvement on BMB; an L3 SUVmean below 1.4 resulted in an NPV of 100%. CONCLUSION: In newly diagnosed FL, PET/CT-detected bone and splenic involvement is highly specific for a positive BMB, and very low SUV values (<2.0 SUVmax and < 1.4 SUVmean ) in the lumbar spine have a high NPV for a negative BMB. Routine BMB may be obviated in these patients. BMB remains necessary to definitively exclude bone marrow involvement in a large majority of patients with a negative PET. IMPLICATIONS FOR PRACTICE: Predicting early clinical failure in follicular lymphoma (FL) is important but difficult. Bone marrow involvement by FL is associated with early clinical failure, and determining this involvement is a key component of the initial staging. This study highlights that in certain patients, positron emission tomography/computed tomography is sufficient in determining bone or marrow involvement, without the need for a confirmatory bone marrow biopsy (BMB). An algorithm is provided based on these findings to help clinicians determine which patients would benefit from BMB and when it can be avoided.

Role of imaging in multiple myeloma.

With rapid advancements in the diagnosis and treatment of multiple myeloma (MM), imaging has become instrumental in detection of intramedullary and extramedullary disease, providing prognostic information, and assessing therapeutic efficacy. Whole-body low dose computed tomography (WBLDCT) has emerged as the study of choice to detect osteolytic bone disease. Positron emission tomography/computed tomography (PET/CT) combines functional and morphologic information to identify MM disease activity and assess treatment response. Magnetic resonance imaging (MRI) has excellent soft-tissue contrast and is the modality of choice for bone marrow evaluation. This review focuses on the imaging modalities available for MM patient management, highlighting advantages, disadvantages, and applications of each.

Quantitative Musculoskeletal Tumor Imaging.

The role of quantitative magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT) techniques continues to grow and evolve in the evaluation of musculoskeletal tumors. In this review we discuss the MRI quantitative techniques of volumetric measurement, chemical shift imaging, diffusion-weighted imaging, elastography, spectroscopy, and dynamic contrast enhancement. We also review quantitative PET techniques in the evaluation of musculoskeletal tumors, as well as virtual surgical planning and three-dimensional printing.

Extraneural perineurioma: CT and MRI imaging characteristics.

OBJECTIVE: To examine the CT and MRI characteristics of extraneural perineuriomas. MATERIALS AND METHODS: With IRB approval, our institutional imaging database was retrospectively reviewed for cases of pathologically proven extraneural perineuriomas. CT and MRI features were recorded, correlative imaging analyzed, and the electronic medical record cross-referenced. RESULTS: We identified ten patients [(seven males, three females, mean age 49.4 ± 18.3 years (range, 16-70 years)]. All cases were pathologically confirmed. Nine cases were conventional soft tissue extraneural perineuriomas, including one with "reticular" features and one with histologic features of malignancy; the tenth case contained admixed Schwann cells (hybrid perineurioma/schwannoma). Six out of ten patients underwent CT and ten of ten MRI evaluation. Nine out of ten MRIs were performed with IV contrast. Five lesions were subcutaneous, four intermuscular, and one intramuscular. Mean lesion diameter was 4.3 ± 2.7 cm (range, 0.9-10.2 cm). Nine out of ten lesions were well circumscribed; one had irregular margins. On CT, five of six were hypodense and one isodense compared to skeletal muscle. Most lesions were T1 isointense (5/10) or hypointense (4/10) and T2 hyperintense (7/10) relative to skeletal muscle, and demonstrated solid enhancement (6/9). There was no evidence of muscular denervation on any MRI exam, and a nerve of origin was identified in two out of ten cases. CONCLUSIONS: Extraneural perineuriomas have a distinctly different imaging appearance from intraneural perineuriomas, manifesting as rounded or ovoid soft tissue masses, without evidence of muscular denervation, and usually without an apparent nerve of origin. Because these features mimic other benign and malignant soft tissue lesions, including sarcomas, biopsy or excision is needed for definitive diagnosis.

Unusual manifestations of diffuse-type tenosynovial giant cell tumor in two patients: importance of radiologic-pathologic correlation.

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.

Neuromuscular choristoma-associated desmoid-type fibromatosis: Establishing a nerve territory concept.

INTRODUCTION: Desmoid-type fibromatosis (DTF) frequently arises in patients with neuromuscular choristoma (NMC). We hypothesize that NMC-associated DTF occurs in soft tissues innervated by the NMC-affected nerve, and arises from CTNNB1-mutated (myo) fibroblasts within or directly adjacent to the NMC. MATERIALS AND METHODS: A retrospective review of patients treated at our institution was performed for patients with biopsy-confirmed diagnosis of NMC-DTF. Clinical presentation, physical examination, electrodiagnostic findings and radiological features (MR and FDG PET/CT images for each NMC-DTF) and pathologic re-review of available materials were analyzed. A literature review was also performed. RESULTS: Eight patients from our institution met the inclusion criteria. All patients presented with neuropathic symptoms and soft tissue or bone changes in the nerve territory innervated by the NMC. All MR images (N=8 cases) showed the characteristic features of NMC, and also showed direct contact between unifocal (N=5) or multifocal (N=3) DTF(s) and the NMC-affected nerve NMC. FDG PET/CT (N=2 cases) showed diffuse, increased FDG uptake along the entire affected nerve segment, contiguous with the FDG-avid DTF. In all cases, the DTFs arose in the soft tissues of the NMC-affected nerve's territory. No patient developed DTF at any other anatomic site. CONCLUSIONS: These data demonstrate that NMC-DTF arises solely within the NMC-affected nerve territory, and has direct contact with the NMC itself. Based on all these findings and the multifocality of NMC in several cases, we recommend imaging and surveillance of the entire NMC-affected nerve (from spine to distal extremity) to identify clinically-occult DTF in patients with NMC.

Molecular characterization of known and novel ACVR1 variants in phenotypes of aberrant ossification.

Diffuse idiopathic skeletal hyperostosis (DISH) is a disorder principally characterized by calcification and ossification of spinal ligaments and entheses. Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant disabling disorder characterized by progressive ossification of skeletal muscle, fascia, tendons, and ligaments. These conditions manifest phenotypic overlap in the ossification of tendons and ligaments. We describe herein a patient with DISH, exhibiting heterotopic ossification of the posterior longitudinal ligament where clinical whole exome sequencing identified a variant within ACVR1, a gene implicated in FOP. This variant, p.K400E, is a novel variant, not identified previously, and occurs in a highly conserved region across orthologs. We used sequence-based predicative algorithms, molecular modeling, and molecular dynamics simulations, to test the potential for p.K400E to alter the structure and dynamics of ACVR1. We applied the same modeling and simulation methods to established FOP variants, to identify the detailed effects that they have on the ACVR1 protein, as well as to act as positive controls against which the effects of p.K400E could be evaluated. Our in silico molecular analyses support p.K400E as altering the behavior of ACVR1. In addition, functional testing to measure the effect of this variant on BMP-pSMAD 1/5/8 target genes was carried out which revealed this variant to cause increased ID1 and Msx2 expression compared with the wild-type receptor. This analysis supports the potential for the variant of uncertain significance to contribute to the patient's phenotype.

Detection of extranodal and spleen involvement by FDG-PET imaging predicts adverse survival in untreated follicular lymphoma.

Predicting early clinical failure in patients with untreated follicular lymphoma (FL) is important but difficult. This study aimed to determine the incidence and patterns of extranodal (EN) and spleen disease using PET/CT, and assess their utility in predicting early clinical failure. PET/CT images from 613 cases of untreated FL (2003-2016) were reviewed. The location and number of EN sites, patterns of bone involvement, and splenic involvement were recorded. Outcomes were assessed using event-free survival (EFS), overall survival (OS), and early clinical failure at 24 months (EFS24). So, 49% (301/613) of patients had PET/CT-detected EN involvement, and 28% (171/613) had spleen involvement. The presence of ≥2 EN sites, spleen, bone or soft tissue involvement all predicted failure to achieve EFS24. Presence of ≥2 EN sites and bone involvement pattern were also predictive of OS in a univariate analysis. In a multivariate analysis with FLIPI-2 factors, spleen involvement, pattern of bone involvement, and soft tissue involvement independently predicted a lower EFS (HR 1.49 (1.11-2.00), P = .007; HR 1.71 (1.10-2.65), P = .017; and HR 1.67 (1.06-2.62), P = .026, respectively). When the multivariate analysis was performed using PRIMA-PI factors (marrow and B2M), the number of EN sites was an independent prognostic factor for inferior OS (HR 2.28; P = .05). Baseline PET/CT identifies EN involvement in nearly half of patients with untreated FL. The presence of ≥2 EN sites, bone, soft tissue, or splenic involvement predicts early clinical failure. These results, when combined with other factors, may better identify high-risk patients and guide therapy.

Imaging features of phosphaturic mesenchymal tumors.

OBJECTIVE: To examine the CT and MR imaging features of phosphaturic mesenchymal tumors (PMTs). MATERIALS AND METHODS: With IRB approval, our institutional radiology/pathology database was reviewed for pathologically-proven PMTs. CT and MRI examinations were reviewed in consensus noting several imaging features, and if available, comparative molecular imaging tests were analyzed. RESULTS: We identified 39 patients (21 male, 18 females) with 40 PMTs [mean age, 52.9 ± 14.9 years (range, 14-78)], including 20 bone and 20 soft tissue lesions. Mean maximal lesion diameter was 3.4 ± 2.0 cm (range, 1.1-9.8). 12/18 primary bone lesions (66.6%) were osteolytic and 15/20 (75.0%) had a narrow zone of transition. Internal matrix was present in 18/32 (56.3%) lesions. PMTs were most commonly T1 isointense (31/37, 83.8%), T2 hyperintense (14/36, 38.9%), and solidly enhancing (21/30, 70.0%). The majority (32/36, 88.9%) contained areas of dark T2 signal. 8/9 PMTs were positive by 99mTc-sestamibi scintigraphy, 2/4 by 111In-pentetreotide scintigraphy, 2/2 by 68Ga-DOTATATE PET/CT and 11/13 by 18F-FDG PET/CT. On FDG PET/CT, the mean SUVmax was 4.1 ± 2.5 (range, 1.5-10.8). CONCLUSIONS: Osseous PMTs are commonly osteolytic with a narrow zone of transition. Both bone and soft tissue PMTs often contain matrix and areas of dark T2 signal on MRI, independent of the presence of matrix. However, PMTs may mimic other bone and soft tissue neoplasms, including fibrous dysplasia, tenosynovial giant cell tumor, and even atypical lipomatous tumor. As such, clinical presentation and laboratory correlation are critical to PMT recognition and accurate diagnosis.

B-cell peripheral neurolymphomatosis: MRI and 18F-FDG PET/CT imaging characteristics.

OBJECTIVE: To examine the MRI and 18F-FDG PET/CT imaging characteristics of peripheral neurolymphomatosis. MATERIALS AND METHODS: All institutional cases of neurolymphomatosis with an MRI or 18F-FDG PET/CT from 2000 to 2017 were retrospectively reviewed. Included cases were biopsy-proven neurolymphomatosis or lymphoma patients with clinical and imaging evidence of neurolymphomatosis that resolved after chemotherapy. Multiple imaging parameters and clinical characteristics were recorded. RESULTS: There were 27 cases of B-cell neurolymphomatosis in 25 patients (18 M, 7 F; mean age 64.6 ± 10.0 years). Of the total cases, 85% (23/27) were biopsy-proven. Most were diagnosed after disease progression or recurrence (20/27, 74%), and presented with isolated nerve involvement (18/27, 67%). Bone marrow biopsy (17/19, 89%) and CSF cytology (16/23, 70%) were usually negative. On 18F-FDG PET/CT, neurolymphomatosis presented as a linear or fusiform (23/26, 88%), FDG-avid (average SUVmax: 7.1 ± 4.5, range, 1.5-17.0) mass, and on MRI as a T2-weighted hyperintense (21/22, 95%), enhancing (21/22, 95%), linear or fusiform mass (19/22, 86%), with associated muscle denervation (14/22, 64%). FDG avidity was significantly higher in patients with muscular denervation on MRI (mean SUVmax 8.2 ± 4.6 vs. 4.3 ± 2.3, p = 0.04). CONCLUSIONS: B-cell neurolymphomatosis most commonly manifests as T2-weighted hyperintense, enhancing linear or fusiform neural enlargement associated with muscular denervation on MRI, with intense FDG activity on PET/CT. It is most often an isolated site of disease, presenting after progression or recurrence. A familiarity with the imaging appearance of neurolymphomatosis can help refine the differential diagnosis, direct biopsy, and aid in accurate diagnosis.

Applications of PET-MRI in musculoskeletal disease.

New integrated PET-MRI systems potentially provide a complete imaging modality for diagnosis and evaluation of musculoskeletal disease. MRI is able to provide excellent high-resolution morphologic information with multiple contrast mechanisms that has made it the imaging modality of choice in evaluation of many musculoskeletal disorders. PET offers incomparable abilities to provide quantitative information about molecular and physiologic changes that often precede structural and biochemical changes. In combination, hybrid PET-MRI can enhance imaging of musculoskeletal disorders through early detection of disease as well as improved diagnostic sensitivity and specificity. The purpose of this article is to review emerging applications of PET-MRI in musculoskeletal disease. Both clinical applications of malignant musculoskeletal disease as well as new opportunities to incorporate the molecular capabilities of nuclear imaging into studies of nononcologic musculoskeletal disease are discussed. Lastly, we discuss some of the technical considerations and challenges of PET-MRI as they specifically relate to musculoskeletal disease. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 3 J. Magn. Reson. Imaging 2018;48:27-47.