Edema Surrounding Benign Tumors and Tumor-Like Lesions

Objective To explore the incidence and significance of intra- and extra-osseous edema associated with benign tumors and tumor-like diseases. Methods Magnetic resonance imaging (MRI) data from 300 benign osseous tumors and tumor-like diseases diagnosed by pathology were retrospectively reviewed. Borderline tumors, cases associated with pathological fractures, and skull lesions were excluded from the study. Bone marrow and soft tissue edema were defined on T2WI with fat suppression on MRI in all cases. The incidence rate of edema in benign tumors and tumor-like diseases was determined using the χ2 test. The preoperative diagnoses were reviewed, and the effect of edema on the differential diagnosis of benign and malignant tumors was analyzed. Results The incidence rate of bone marrow and soft tissue edema associated with benign tumors and tumor-like diseases was 35.7% (107/300), including 84.4% (27/32) Langerhans cell histiocytosis, 86.4% (19/22) osteoblastoma, 93.9% (31/33) osteoid osteoma, and 85.2% (23/27) chondroblastoma cases. There was no statistically significant difference in the incidence of edema among the four diseases (χ2 = 1.7, P > 0.05). Of 107 cases associated with edema, 49 (45.8%) were misdiagnosed as malignant tumors by MRI preoperatively. Conclusion Bone marrow and soft tissue edema are a common finding associated with benign bone tumors and tumor-like diseases, and they are frequently detected in Langerhans cell histiocytosis, osteoblastoma, osteoid osteoma, and chondroblastoma.


Introduction
e incidence of bone tumors and tumor-like lesions is 2%-3%, and the ratio of benign to malignant tumors is 0.83 : 1 [1]. e incidence of benign tumors and tumor-like lesions is 0.91%-1.36%; however, the incidence may be underestimated because benign lesions are usually asymptomatic and frequently remain undiscovered [2]. Benign tumors and tumor-like lesions are more likely to occur in patients aged 11-30 years with a ratio of men to women of 1.5 : 1, and the most common locations are the femur and tibia. e treatment of benign bone tumors and tumor-like lesions includes surgery, chemotherapy, radiotherapy, and interventional therapy. Asymptomatic benign tumors and tumor-like lesions can be monitored as a follow-up [3].
Bone marrow and so tissue edema are a common finding associated with benign and malignant tumors or tumor-like diseases. In routine clinical practice, a lesion that is associated with remarkable surrounding edema is considered as an invasive active tumor by radiologists [4][5][6]. Yamamura et al. [7] showed that obvious surrounding edema disappeared and high serum levels of prostaglandin decreased a er the resection of lesions in patients with osteoid osteoma and osteoblastoma.
is phenomenon suggests that the inflammatory medium may lead to the development of so tissue and marrow edema. e destruction of trabeculae increased pressure inside the bone marrow, discharging of inflammatory medium, and liquid exudate from capillary vessels inside tumors were suggested as possible causes of marrow and so tissue edema surrounding a lesion [8,9]. Hence, differentiating benign from malignant lesions with surrounding edema is important to prevent unnecessary surgery or over-resection of lesions with a larger area [10]. We retrospectively reviewed pathologically proven benign bone tumors and tumor-like diseases to explore the occurrence rate and characteristics of edema surrounding these lesions. e diagnosis of bone marrow and so tissue edema was based on the following criteria: magnetic resonance imaging (MRI) was used because it is sensitive for the detection of edema [5]. An abnormal signal, such as long T1 and long T2 compared with the surrounding normal bone marrow or so tissue, and a high signal on T2WI with fat-suppression or a STIR sequence with a vague margin were considered indicators of bone marrow or so tissue edema [6].

Patients.
Between January 2016 and January 2019, 300 pathologically proven (a er surgical operation or biopsy) benign bone tumors and tumor-like diseases with integrated MR data from our hospital were retrospectively analyzed. Informed consent was obtained from all participants included in the study. Borderline tumors such as giant-cell tumor of bone and desmoplastic fibroma, lesions with pathological fractures, and cranial lesions were excluded from the study. A total of 300 patients were included in the study, and the age and gender distribution of participants are shown in Figure 1.

Examination.
All patients underwent MR plain scan within 10 days before the surgical procedure or other treatments. Enhanced MRI was performed in 50 cases. Followup MRI was performed 2 weeks to 3 months a er treatment. e location of lesions is shown in Figure 2. MRI examination was performed using the GE Signa HDXT 3.0T MR scanner. e MR scan sequence and parameters are shown in Table 1.

Image Analysis.
Two senior musculoskeletal radiologists reviewed all images on the PACS system, and differences in opinion were resolved by consensus. e presence of bone marrow and so tissue edema was first determined using MR images. e types of tumor and tumor-like diseases associated with bone marrow and so tissue edema and the numbers of preoperative misdiagnosis were determined using the pathology results. Post-operative changes in the incidence of edema were assessed.

Statistical Analysis.
e occurrence rates of surrounding edema in different kinds of benign bone tumor and tumor-like diseases were compared. Statistical analyses were performed using the Chi-square test and SPSS so ware (version 20.0, IBM   Corporation, Armonk, NY). All values were two-sided, and a -value <0.05 was considered statistically significant.

Pathological Diagnosis.
e 300 cases of benign bone tumors and tumor-like diseases included osteoid osteoma, osteoblastoma (Figure 3 Table 2.

MRI Findings.
Occurrence rate of surrounding edema: Surrounding edema was detected in 107 cases and the occurrence rate was 35.7% (107/300), among which eight cases (7.5%, 8/107) were only surrounding bone marrow edema ( Figure 4(b)), six cases (5.6%, 6/107) were only surrounding so tissue edema (Figure 3(b)), and 93 cases (86.9%, 93/107) were surrounding bone marrow edema together with so tissue edema ( Figure 5(b)). Contrast-enhanced MRI was performed in 50 cases, of which 38 were associated with surrounding edema. Among the 38 cases enhanced by contrast agent injection, the degree of enhancement of the edema was higher than that of the lesion in 12 cases, lower than that of the lesion in 13 cases, and comparable to that of the lesion in 13 cases (Table 3).

Follow-Up and Changes in the Surrounding Edema a er
Treatment. Among 107 cases with surrounding edema, 89 underwent surgery; 19 cases were followed-up by MR during a period of 2 weeks to 3 months postoperatively. e surrounding edema disappeared a er surgery in 17 cases, including  benign bone tumors and tumor-like diseases. In the present study, the occurrence rate of surrounding edema was 84.4% (27/32) in Langerhans cell histiocytosis, which was slightly lower than that of 91% (20/22) reported by Jeh et al. [12]. e occurrence rate of surrounding edema in osteoblastoma was 86.4% (19/22), which was comparable to that of other studies. Kroon et al. [13] reported that the three cases of osteoblastoma analyzed were associated with surrounding edema. Shaikh et al. [14] reported that 10 of 11 cases of vertebral osteoblastoma were accompanied by surrounding edema. e occurrence rate of surrounding edema in osteoid osteoma in the present study was 93.9% (31/33), which was higher than that of 88.37% (38/43) reported by Davies et al. [15]. Surrounding edema was found in 85.2% (23/27) of chondroblastoma cases in the present study, which was comparable to the rate of 77-92% reported previously [16,17]. Although the three cases of capillary hemangioma of bone included in the present study were associated with surrounding edema, the sample was too small, and the results need to be confirmed in a greater number of cases. Surrounding edema was found in 18.2% (2/11) of aneurysmal bone cysts in our study, which was a lower rate than that of 33% reported by Woertler et al. [18]. Because aneurysmal bone cysts are o en accompanied by pathological fracture, whether the surrounding edema is caused by the pathological fracture or the expanding cortex in cases of aneurysmal bone cyst needs to be determined.

e Performance of Contrast-Enhanced MRI.
Among 50 cases that underwent contrast-enhanced MRI, 38 had surrounding edema, and all cases showed enhancement. No new surrounding edema was observed in the enhanced images, and there was no significant difference in the incidence of surrounding edema between the plain scan and the enhanced scan. ese results were consistent with those reported by Giraudo et al. [19]. e boundaries of surrounding edema and lesions are clearer in contrast enhanced than in non-contrast enhanced images, as shown by Liu et al. [20], who reported that enhanced MRI imaging can depict osteoid osteomas with greater accuracy than non-enhanced MRI, facilitating the detection of the size and morphology of the lesions.

Limitations of the Study.
e present study had several limitations. Firstly, we did not examine the relationship between tumor size and surrounding edema or the relationship between the size of edema and the properties of the lesions. Secondly, although contrast-enhanced MRI was included, dynamic contrast-enhanced MRI was not performed.
irdly, bone marrow and so tissue edema were not examined separately because they were detected together in most cases (86.9%, 93/107). In addition, the disease types included in the present study were limited, and the inclusion of a larger cohort is needed. Foti et al. [21] reported that dual-energy CT represents an accurate imaging tool for bone marrow edema of the ankle compared with MRI. We did not perform a comparative study of MRI and dual-energy CT.
tumor nests in second surgical operations, the surrounding edema disappeared (Figures 6(a)-6(c)). e pathology of the specimen from the second operation showed fibro-vascular mesenchyma between trabeculae constructed by osteoid tissue or woven bone ( Figure 6(d)).
Four cases of Langerhans cell histiocytosis underwent chemotherapy; the range of surrounding edema was reduced a er 2 weeks. Two cases underwent radiotherapy, and the range of edema was reduced a er 2 weeks.
Twelve cases did not receive treatment; there was no significant change in the surrounding edema a er 2 weeks.

Occurrence Rate of Surrounding Edema in Benign Bone Tumors and Tumor-Like Diseases.
e results of the study by Kroon et al. [11] showed that surrounding bone marrow edema and so tissue edema are detected in 42% (10/24) and 58% (14/24) of benign bone tumors and tumor-like diseases, respectively, which was a higher rate than that of the present study at 35.7% (107/300). One possible explanation for this difference is that the patient population was small (24 cases) and there were few disease types (7 kinds) included in the study by Kroon et al. [11]. e occurrence of surrounding edema is closely related to the numbers of patients and disease types. In the present study, surrounding edema was not detected in nonossifying fibroma, fibrous dysplasia of bone, chondroma, simple bone cyst, osteoma, and ganglion cyst of bone. e inclusion of additional cases of these diseases may have decreased the occurrence rate of surrounding edema. Regardless of the higher or lower occurrence rate of edema, the above results indicate that surrounding edema was not a specific indicator of malignant bone tumors.

Surrounding Edema in Different Types of Benign Bone Tumor and Tumor-Like Diseases.
e occurrence rates of surrounding edema are relatively high in certain kinds of

Conclusion
Marrow and so tissue edema are a common occurrence associated with benign bone tumors and tumor-like diseases. ere was no statistically significant difference in the incidence of edema between Langerhans cell histiocytosis, osteoblastoma, osteoid osteoma, and chondroblastoma.
Data Availability e data used to support the findings of this study are available from the corresponding upon request.

Ethical Approval
is article does not contain any studies with human participants or animals performed by any of the authors.