[en] purpose: evaluate the contribution of PET/CT with ¹⁸F.D.G. in complement of conventional imaging in the initial assessment and the assessment of follow-up of rhabdomyosarcomas in the pediatrics population. Conclusions: the PET/CT with ¹⁸F.D.G. is an efficient technique to evaluate the child rhabdomyosarcomas, in complement of conventional imaging, especially for the bone, osteo-medullary ganglion staging as well as the therapy strategy and the research of the primitive site. We suggest the use of the PET/CT to replace the bone scintigraphy, in complement of local MRI and CT for the initial assessment, the follow-up assessment of pediatrics rhabdomyosarcomas. (N.C.)

[en] Introduction. - Small cell lung cancer (S.C.L.C.) is a neuroendocrine tumour representing 20% of bronchopulmonary cancers. Its metastatic potential is high, so 2/3 of diagnoses are made at disseminated stage. Anti H.u. antibodies are part of the anti neuronal antibodies, often associated to S.C.L.C.. However, 16% of cancers have positive anti H.u. with no para neoplastic syndrome (P.N.S.). (Graus, Brain, 2001). P.N.S. associated with anti H.u. are encephalomyelitis, sensitive neuropathy, chronic pseudo intestinal obstruction, cerebellar degeneration and limbic encephalitis. Case report. - A 75-year-old patient was hospitalized for exploration of an atypical tri-facial neuralgia. Anti H.u. antibodies were found and P.N.S. of a S.C.L.C. was therefore suspected. The biopsy of a thoracic parietal adenopathy confirmed the diagnostic of S.C.L.C. metastasis. Conventional imaging and ¹⁸F-FDG (Fluorodeoxyglucose) PET/CT (Positron Emission Tomography/Computed Tomography)) did not localize the primary tumour, despite advanced dissemination stage, only showing lymphatic secondary locations at the left axillary and under the diaphragm areas. Literature review. - Younes-Mhenni (Brain, 2004, 20 patients); and Linke (Neurology, 2004, 13 patients) studied patients presenting with anti H.u. antibodies (13 and eight respectively) and other anti neuronal antibodies (Y.o., Ri, C.V.2, Tr) associated with different cancers. PET sensitivity was respectively 83.3 and 90% with a specificity of 25 and 67%. In both series, specificity of anti H.u. antibodies for S.C.L.C. was estimated at 53% and 62.5%. Size is a limiting factor for S.C.L.C. detection and Watanabe (Nihon Kokyuki Gakkai Zasshi, 2001) showed that sensitivity for detection of less than 1 cm tumour was 0% in five patients. Moreover, P.N.S. can precess S.C.L.C. detection for many years and PET/CT has to be repeated. (Gaillard, Revue neurologique, 2005).In two other studies (Schumacher, EJNM, 2001, 30 patients; and Niho, Lung Cancer, 2007, 63 patients), PET and T.D.M. have been compared, showing the superiority of PET at initial staging for lymphatic node and distant metastases detection, leading to therapeutic modifications in 8% of cases. In a in vitro study, Fischer and al. (EJNMMI, 2006) showed that the number of cancerous cells to obtain a positive signal with PET was different according to the anatomo-pathological type of tumour, with a detection limit increased by a factor of 10 for S.C.L.C. detection compared to glioblastoma. Most of time S.C.L.C. are located at lung level but many extra-pulmonary locations are known. Immunohistochemical markers can help diagnosis, for instance association between T.T.F.1 and pulmonary location, without being completely specific (Ghosh, Current problems in surgery, 2005). Conclusion. - Despite some false negative, PET is a precious examination for diagnosis and staging of documented P.N.S., in particular suspicion of S.C.L.C. with anti H.u. antibodies, leading to repeat the examinations in case of negativity. (authors)

[en] OBJECTIVE: this prospective study evaluates the feasibility in current clinical practice of contrast enhanced CT-scan for diagnosis purpose, performed during 18FDG PET-CT study with a PET/CT tomography. METHOD: 25 patients underwent FDG imaging for lymphoma staging. The PET scan was done immediately after the usual low dose CT (lCT). A second CT scan was consequently acquired, by using classical diagnosis CT parameters (dCT) and iodinated contrast. For each patient, all CT attenuation correction (CTAC) PET images were visually compared. Density in Hounsfield units (HU) and maximum Standardized Uptake Value (SUVmax) were then measured on different organs and up to 5 specific lymphoma localizations (total of 294 measurements). RESULTS: Visual analysis was similar for the 2 modalities, without discordant interpretation for the pathologic sites. SUVmax means and standard deviation of each organ for lCTAC and dCTAC were comparable. The equation of the fitted multiple linear regression model was: dCT=0.0748191 + 1.17024*lCT (98.71%; p < 0.01). CONCLUSION: These first results allow the use of injected CT scan, before the PET scan acquisition for lymphoma staging with this PET-CT scan, not affected by the height atomic number and elevated density. A great benefit is therefore obtained on diagnostic, logistic and radioprotection purposes.

[en] The purpose of this retrospective study is to compare the diagnostic efficiency of the bone scintigraphy compared to the PET with ¹⁸F-F.D.G. in the detection of primitive or secondary bone injuries of soft tissues sarcomas or bone sarcomas. In view of our results and analysis of literature, performing a bone scan of Ewing sarcoma and soft tissue sarcomas do not seem useful. It retains an interest in the case of osteosarcoma. (N.C.)

[en] Introduction. - Malignant lymphoma is a heterogeneous and widespread disease. The morphological response assessment is currently based on the choice of target lesions at baseline, defined by size criteria on enhanced CT (eCT). FDG PET/CT is now commonly used at staging and the aim of this study was to evaluate the relevance of using metabolic criteria rather than size criteria to define the target lesions. Patients and methods. - Fifty-nine patients with aggressive lymphoma were retrospectively included. Target lesions were chosen by two radiologists on eCT and by two nuclear physicians on PET/CT. Response assessment, based on the sum of the products of the greatest diameters of up to six target lesions chosen either by size or metabolic criteria, was computed and compared to a clinical gold standard (GS) for each patient. Interobserver agreement and comparison to the GS were assessed with kappa (κ) and intraclass correlation (ICC) statistics. Results. - The spatial distribution of target nodal areas was equivalent among eCT and PET/CT readers with a maximum of target lesions in cervical and mediastinal areas. Choosing with PET/CT led to significant heterogeneity in the size of target lesions when compared with eCT alone (P = 0.03). Interobserver agreement for quantifying the response rate was equivalent in both groups. However, there was a greater correlation to the response of the GS when using PET/CT to target the patient (k = 0.64 vs. 0.47) and an increased rate of complete responses. Conclusions. - Metabolic criteria can replace current size criteria to define target lesions on FDG PET/CT. The morphological response rate appears accurate with an increased rate of complete responses after therapy and a better correlation to the haematological standard of reference. (authors)