Case Reports

A 17-year-old boy presented to our department with dyspnea and diplopia lasted for approximately one month. MRI demonstrated 6 x 4 x 4 cm mass with irregular contour in the orbital region. On MRI, one left cervical and one submandibular lymph node were also detected. Embryonal rhabdomyosarcoma (RMS) was diagnosed by biopsy. To better define the lesion prior to surgery and in a search for distant metastases, we performed a combined FDG PET/CT whole-body scan. PET/CT revealed the primary lesion with irregular contours. Maximum calculated standardized uptake value (SUVmax) of the lesion was 9.82 PET/CT also demonstrated bilateral cervical and submandibular lymph nodes showing intense FDG accumulation (SUVmax 9.44). Additionally, there were pathological accumulations in pelvic bones, bilateral proximal femora, bilateral humeri, scapula, sternum, clavicles, ribs, and vertebrae (Figure 1). The patient could not undergo complete resection because of the local invasion on computed tomography and magnetic resonance imaging and distant metastases. Chemoradiotherapy was initiated. In our patient, FDG-PET combined with simultaneous low-dose CT transmission tomography, permitted the detection of distant metastases that was not clinically evident. PET/CT also showed pathological contralateral cervical lymph nodes that were not seen on MRI. The patient was upstaged on FDG PET/CT. The orbit is one of the most common sites for RMS. Most of the patients with orbital sarcoma present with localized disease. Patients presenting metastatic disease at initial diagnosis are uncommon. However, bone marrow involvement counts among the most common metastases, especially in the presence of extensive local invasion (1). Embryonal RMS is the most common histology in patients with non-metastatic orbital sarcoma. In Stage 4 cases, embryonal RMS was found in about half of the cases (2). There are few reports about the efficacy of FDG PET/CT in the localization and detection of soft tissue sarcomas (3,4). In a study by Tateishi et al (5), 11 of the 35 patients had distant metastases detected by FDG PET/CT, which were not identified by conventional radiologic evaluation. FDG PET/CT was found more accurate than conventional imaging regarding clinical staging and re-staging of patients with rhabdomyosarcomas. Although, overall likelihood of bone involvement is low in orbital embryonal RMS at initial diagnosis, FDG PET/CT may be useful in patients with a higher likelihood of distant metastases.