Beyond schwannomas and neurofibromas: a radiological and histopathological review of lesser-known benign lesions that arise in association with peripheral nerves.

Peripheral nerve sheath tumors comprise a significant percentage of both benign and malignant soft tissue tumors. The vast majority of these lesions are schwannomas and neurofibromas, which most radiologists are familiar with including the well-described multimodality imaging features. However, numerous additional often under-recognized benign entities associated with nerves exist. These rarer entities are becoming increasingly encountered with the proliferation of cross-sectional imaging, particularly magnetic resonance imaging (MRI). It is important for the radiologist to have a basic understanding of these entities as many have near-pathognomonic MR imaging features as well as specific clinical presentations that when interpreted in concert, often allows for a limited differential or single best diagnosis. The ability to provide a prospective, pre-intervention diagnosis based solely on imaging and clinical presentation is crucial as several of these entities are "do not touch" lesions, for which even a biopsy may have deleterious consequences. To our knowledge, the majority of these benign entities associated with nerves have only been described in scattered case reports or small case series. Therefore, the aim of this article is to provide a radiopathologic comprehensive review of these benign entities that arise in association with nerves with a focus on characteristic MRI features, unique histopathologic findings, and entity specific clinical exam findings/presentation.

Soft-Tissue Tumors of the Hand-Imaging Features.

Imaging studies of the hands and fingers are common, and radiologists are generally comfortable with traumatic and degenerative conditions which arise frequently in daily practice. However, a variety of common and uncommon soft-tissue tumors also occur in the hand, the appropriate diagnosis of which can be a source of confusion for both clinicians and radiologists. These lesions often have overlapping imaging characteristics; however, a structured approach can help provide a focused differential diagnosis and impact further workup and management. We discuss several such tumors, categorizing them as cystic-appearing, noncystic masses along tendons and aponeuroses, adipocytic tumors, vascular lesions, and miscellaneous lesions with imaging features that can aid diagnosis.

Update on Imaging of Knee Arthroplasties: Normal Findings and Hardware Complications.

Total knee arthroplasty (TKA) is the most common joint replacement performed. This article reviews the normal appearance of TKA including the most common types of arthroplasties as well as complications. Common complications at the present time are infection, aseptic loosening, and instability. Rarer complications such as polyethylene wear, periprosthetic fracture, and soft tissue pathology are also discussed. Although the mainstay of imaging is radiographs, newer techniques in TKA imaging such as computed tomography and magnetic resonance imaging are also reviewed.

Infarct-Associated Bone Sarcomas: Multimodality Imaging Findings.

OBJECTIVE: The objective of our study was to characterize infarct-associated bone sarcoma and its imaging features. MATERIALS AND METHODS: Our databases were searched for instances of sarcoma arising in association with osteonecrosis. Demographic and imaging data were recorded. The imaging studies of 258 patients with sarcomas were reviewed to determine whether underlying osteonecrosis was present. Radiographic and MRI studies of patients with bone infarction were reviewed to categorize the various appearances of infarction and to determine if sarcomas tended to arise in a particular pattern. A literature review was performed. RESULTS: Nine infarct-associated bone sarcomas were found in eight patients: seven malignant fibrous histiocytomas (MFHs) and two osteosarcomas. All occurred in the femur or tibia; multifocal infarction was documented in all patients except one. Sarcomas were commonly associated with a so-called "mature"-type pattern of osteonecrosis-that is, with well-defined calcified margins. Osteolysis of infarct-associated MFHs was often overlooked at initial presentation and was often detected only after pathologic fracture. CT and MRI revealed cortical penetration in all cases; infarct margin disruption was evident, but preservation of fat within the infarct was typical. Increased radiotracer activity with relative central photopenia was characteristic of large infarct-associated bone sarcomas on scintigraphy. All lesions, including those treated at our institution and those found in the literature, were metaphyseal or diaphyseal, and although epiphyseal extension of sarcoma from a metadiaphyseal infarct was common, no purely epiphyseal lesions were encountered. CONCLUSION: Radiologists must remain vigilant for this rare occurrence, especially in patients with new pain in an area of known bone infarction.

Imaging Diagnosis of Solitary Tumors of the Phalanges and Metacarpals of the Hand.

OBJECTIVE: Tumors and tumorlike lesions of the tubular bones of the hand, often incidentally discovered lesions, present a unique but challenging differential diagnosis. CONCLUSION: Imaging, including both radiography and cross-sectional imaging, can allow the radiologist to generate a clinically useful differential diagnosis based on the distinguishing features of these entities. Recognition of these lesions is important because clinical management and treatment by orthopedic oncologists vary depending on the diagnosis.

From tumor to trauma: etiologically deconstructing a unique differential diagnosis of musculoskeletal entities with high signal intensity on T1-weighted MRI.

OBJECTIVE: This article reviews the neoplastic and nonneoplastic abnormalities of the musculoskeletal system that contain high signal intensity on T1-weighted MRI. The physical properties accounting for the increased signal intensity as well as the key clinical and imaging characteristics of each entity are discussed. CONCLUSION: Recognition of high signal intensity within musculoskeletal lesions on T1-weighted MRI can limit the differential diagnosis and can also have important clinical implications.

Osteoma of long bone: an expanding spectrum of imaging findings.

Osteoma of long bone is an extremely rare, benign bone-forming surface lesion with the largest published case series consisting of only 14 patients. The most important and often most difficult lesion to differentiate from osteoma of long bone radiographically is parosteal osteosarcoma, which is a rare, low-grade surface osteosarcoma with the potential for dedifferentiation. Reports of imaging studies of osteoma of long bone depict a well-defined ossified mass arising from the surface of the diaphysis or metadiaphysis of a long bone. A characteristic feature is the homogeneity of the mass, with uniform density near or equal to that of cortical bone from the base of the lesion to its periphery. The 45-year-old female in this case presented with left hip fullness and was subsequently found to have a proximal femoral osteoma, which was unique in that it contained large fatty marrow spaces that corresponded to bands of relatively low density on plain radiography and computed tomography, giving it a heterogeneous appearance atypical of osteoma of long bone. Furthermore, the osteoma reported here was associated with a small but separate nodular focus of ossification in the adjacent soft tissue. These findings led to a presumptive diagnosis of parosteal osteosarcoma with a local soft tissue metastasis or satellite nodule resulting in radical resection of the tumor. Definitive diagnosis of osteoma was made on histology of both the parent lesion and ossified nodule as no neoplastic spindle cell proliferation was present to establish a diagnosis of low-grade osteosarcoma. This represents, to the best of our knowledge, the first such presentation of osteoma of long bone.

Musculoskeletal manifestations of neurofibromatosis type 1.

OBJECTIVE: We will describe and illustrate various musculoskeletal manifestations of neurofibromatosis type 1 (NF1) encountered on imaging studies. CONCLUSION: Because NF1 is one of the most common genetic disorders, radiologists should be familiar with its imaging manifestations.

Musculoskeletal aspiration procedures.

With advances in imaging technology, there has been a significant increase in the number and range of interventional musculoskeletal image-guided procedures. One of the most commonly performed image-guided musculoskeletal interventions is the diagnostic and therapeutic percutaneous aspiration and drainage of multiple types of intra-articular, juxta-articular, and intramuscular pathologic fluid collections. These procedures may be performed under fluoroscopic, ultrasound, computed tomography, or even magnetic resonance guidance depending on the location to be accessed, type of pathology, patient characteristics, and operator preference. Musculoskeletal image-guided aspiration and drainage procedures are minimally invasive and generally very safe while offering valuable diagnostic information as well as therapeutic benefit. This article focuses on the appropriate indications, contraindications, and general technique for accessing the major joints via imaging guidance. For each joint, we discuss pertinent anatomy, appropriate imaging modalities, and preferred approaches to gaining intra-articular access. Additionally, the article discusses some of the more frequently encountered juxta-articular and intramuscular fluid collections that can be accessed and aspirated via percutaneous intervention, with mention of the importance of recognizing extremity sarcomas that can mimic these benign collections.

Factors associated with recurrence of primary aneurysmal bone cysts: is argon beam coagulation an effective adjuvant treatment?

BACKGROUND: Our goal was to assess the effectiveness and safety of argon beam coagulation as an adjuvant treatment for primary aneurysmal bone cysts, to reevaluate the adjuvant effectiveness of the use of a high-speed burr alone, and, secondarily, to identify predictors of aneurysmal bone cyst recurrence. METHODS: We retrospectively reviewed the records of ninety-six patients with primary aneurysmal bone cysts who were managed at our institution from January 1, 1983, to December 31, 2008. Forty patients were managed with curettage, a high-speed burr, and argon beam coagulation; thirty-four were managed with curettage and a high-speed burr without argon beam coagulation; and the remaining twenty-two were managed with curettage with argon beam coagulation alone, curettage with no adjuvant treatment, or resection of the entire lesion. Demographic, clinical, and radiographic data were viewed comparatively for possible predictors of recurrence. Kaplan-Meier survival analysis with a log-rank test was performed to measure association and effectiveness. RESULTS: The median age at the time of diagnosis was fifteen years (range, one to sixty-two years). The median duration of follow-up was 29.5 months (range, zero to 300 months). The overall rate of recurrence of aneurysmal bone cyst after surgical treatment was 11.5%. The rate of recurrence was 20.6% after curettage and high-speed-burr treatment alone and 7.5% after curettage and high-speed-burr treatment plus argon beam coagulation. The five-year Kaplan-Meier survival estimate was 92% for patients managed with curettage and adjuvant treatment with a high-speed burr and argon beam coagulation, compared with 73% for patients managed with curettage and a high-speed burr only (p = 0.060). CONCLUSIONS: Surgical treatment of aneurysmal bone cyst with curettage and adjuvant argon beam coagulation is effective. Postoperative fracture appears to be a common complication of this treatment and needs to be studied further. Treatment with curettage and high-speed burr alone may not reduce recurrence.

Radiofrequency ablation of solitary eosinophilic granuloma of bone.

OBJECTIVE: This article about our initial clinical experience describes the novel application of radiofrequency ablation for the treatment of two cases of solitary eosinophilic granuloma of the bone. CONCLUSION: Technical success was achieved in both cases with a prompt clinical response and no treatment-related complications. To our knowledge, this is the first description of the application of radiofrequency ablation for the treatment of solitary eosinophilic granuloma of the bone.

Pitfalls in MR image interpretation prompting referrals to an orthopedic oncology clinic.

Patients referred to the authors' hospital for evaluation on suspicion of a bone or soft-tissue malignancy frequently present to the Orthopaedic Oncology Clinic with magnetic resonance (MR) images that show typical features of nonmalignant or nonneoplastic entities. The purpose of this article is to review the benign entities that may be mistaken by the radiologist for a malignancy and thus lead to needless referral to an orthopedic oncologist. Normal hematopoietic marrow and marrow edema due to a stress reaction may mimic a neoplasm at MR imaging, but knowledge of the typical patterns and locations of these features allows an accurate radiologic interpretation. The MR imaging appearance of osteonecrosis, Paget disease, benign bone lesions, and rheumatologic conditions may be confusing; in such circumstances, radiographic findings may help formulate a correct diagnosis. Knowledge of the common locations and appearances of bursae and ganglia is necessary so that radiologists do not misinterpret these benign entities as soft-tissue sarcomas. Soft-tissue trauma and inflammation also may mimic tumors at MR imaging, but a familiarity with the imaging patterns of nonneoplastic change in muscle allows the avoidance of misinterpretation. The clinical history, as always, is an important component of proper diagnosis. The radiologist can be especially useful to both the clinician and the patient by recognizing entities that are highly unlikely to represent malignancy and by confidently reporting those entities as benign, thereby sparing the patient an unnecessary trip to the orthopedic oncologist.

Staging of bone tumors: a review with illustrative examples.

OBJECTIVE: The radiologist plays an important role in the workup and staging of bone tumors. The purpose of this article is to review that role and to discuss recent changes to the primary malignant bone tumor staging system developed by the American Joint Committee on Cancer. CONCLUSION: Knowledge of staging parameters for the diagnosis and management of bone tumors will help the radiologist to generate meaningful reports for the referring physician.

Endometriosis of the vastus lateralis muscle.

We report an unusual case of a woman who sought medical attention for a painful mass within her anterolateral left thigh. The patient's symptoms waxed and waned with her menses. Magnetic resonance imaging revealed a 3 cm mass isointense to muscle and surrounded by a rim of decreased signal intensity on T1-weighted images. T2-weighted images with fat saturation revealed a low signal intensity mass with a surrounding rind of high signal intensity edema. Based on its magnetic resonance imaging characteristics, the lesion was initially thought to represent the sequela of prior trauma or perhaps a small fibrous tumor. An excisional biopsy of the mass, however, revealed endometrial tissue, and a pathologic diagnosis of intramuscular endometriosis was rendered.

Multifocal metachronous giant cell tumor in a 15-year-old boy.

We report a case of multifocal metachronous giant cell tumor (GCT) that involved the fibula, tibia, and sacrum of a 15-year-old boy. Multifocal GCT of bone presenting in children is an exceedingly rare phenomenon; however, there is evidence that multifocal GCT presents, on average, at a younger age than solitary GCT. Pediatric radiologists should be aware of this when encountering a single lesion with characteristic radiographic features of GCT and when encountering multiple lytic skeletal lesions.