Eleven-year-old boy with a nasopharyngeal mass.Eleven-year-old boy with a nasopharyngeal mass.
Large mass located in the left nasopharynx demonstrating heterogeneous uptake. The lesion is more active in the periphery (SUVmax 3,2) and has a hypometabolic center. There are no calcifications in the mass. No clear invasion of adjacent bone in low-dose CT.
No suspicious lymph node. No distant lesion.
Langerhans cell histiocytosis
Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood and third most common extra-cranial solid tumor after neuroblastoma and Wilm’s tumor. RMS is thought to derive from primitive mesenchymal cells that are committed to myogenesis. The two main histologic subtypes are embryonal and alveolar.
Common sites of primary disease are the head and neck region, genitourinary tract (GU) and extremities. In the head and neck region, orbital and parameningeal regions (including the middle ear, nasal cavity, paranasal sinuses, nasopharynx and infratemporal fossa) are the most frequently involved. In the GU tract, RMS often arises from the bladder or prostate.
Factors associated with worse prognosis are:
-Age > 10 years
-Tumor size (>5cm) and invasiveness
-Unfavorable primary sites such as parameningeal region, bladder and prostate
The most common site of metastatic disease is lung, followed by bone, bone marrow and lymph nodes.
Roles of FDG PET/CT
Initial results of PET and PET/CT in diagnosis and staging of rhabdomyosarcoma are interesting. Tateishi et al. compared FDG PET/CT and conventional imaging (bone scan, whole body CT and local MRI) in the staging and restaging of rhabdomyosarcoma. Accuracy was similar for nodal staging (97 vs 87 %). However PET/CT was more accurate for distant metastasis detection (89 vs 63%). Ricard et al. also found better sensitivity of FDG PET/CT compared with conventional imaging. The only drawback of FDG PET/CT was the detection of subcentimetric lung nodules.
Prediction of outcome by FDG PET/CT was also evaluated. Baum et al. found that high metabolic activity was a discriminator for overall survivor. Qualitative analysis was performed visually classifying metabolic activity in 3 groups: uptake lower or equal to liver, uptake higher than liver but lower than brain and uptake not discernible from brain (using a gray scale ranging from 0 to 3.5 times average liver activity). Semi quantitative analysis was also performed with a threshold value of 4.6 for SUVmax lesion/SUVmax liver. The authors demonstrated a significant difference in overall survival. Moreover, lymph node involvement and distant metastatic disease were predictive of worst overall survivor.
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