High ¹²³I-MIBG uptake in neuroblastic tumours indicates unfavourable histopathology.

PURPOSE: Scintigraphy using (123)I-metaiodobenzylguanidine ((123)I-MIBG) is widely used for the detection of neuroblastic tumours. The aim of this study was to identify a possible correlation between the uptake intensity on (123)I-MIBG SPECT and histopathology of neuroblastic tumours. METHODS: (123)I-MIBG SPECT examinations were performed in 55 paediatric patients with neuroblastic tumour and compared to histopathology after surgical resection or biopsy at a mean of 2 weeks after SPECT. For each lesion International Neuroblastoma Pathology Classification System (INPC) stage, mitosis karyorrhexis index (MKI), location and a semiquantitative tumour-to-liver count-rate ratio (TLCRR) were determined. Also, the presence or absence of MYCN amplification, p1 deletion, urine catecholamine and neuron-specific enolase blood levels at the time of scanning were recorded. RESULTS: In the 55 patients, 61 lesions were evaluated with (123)I-MIBG SPECT and corresponding histopathological findings were reviewed (11 ganglioneuroma, 11 ganglioneuroblastoma and 39 neuroblastoma). TLCRR was significantly higher in the neuroblastoma group (mean TLCRR 2.7) than in the ganglioneuroblastoma group (mean TLCRR 1.0) and ganglioneuroma group (mean TLCRR 0.7) at the time of primary diagnosis (p < 0.001) and at follow-up (p = 0.039). Intense (123)I-MIBG uptake was found in tumour tissue with a high mitotic activity (MKI-high or MKI-intermediate) after treatment. Four ganglioneuromas (36 %), three ganglioneuroblastomas (27 %) and six neuroblastomas (15 %) were (123)I-MIBG-negative. CONCLUSION: In paediatric patients with peripheral neuroblastic tumours, strong (123)I-MIBG uptake indicates unfavourable histopathology. High uptake was seen in neuroblastomas and in tumours with a high mitotic activity.

The diagnostic value of 18F-FDG PET and MRI in paediatric histiocytosis.

PURPOSE: To analyse the diagnostic value of (18)F-FDG PET and MRI for the evaluation of active lesions in paediatric Langerhans cell histiocytosis. METHODS: We compared 21 (18)F-FDG PET scans with 21 MRI scans (mean time interval 17 days) in 15 patients (11 male, 4 female, age range 4 months to 19 years) with biopsy-proven histiocytosis. Primary criteria for the lesion-based analysis were signs of vital histiocyte infiltrates (bone marrow oedema and contrast enhancement for MRI; SUV greater than the mean SUV of the right liver lobe for PET). PET and MR images were analysed separately and side-by-side. The results were validated by biopsy or follow-up scans after more than 6 months. RESULTS: Of 53 lesions evaluated, 13 were confirmed by histology and 40 on follow-up investigations. The sensitivity and specificity of PET were 67 % and 76 % and of MRI were 81 % and 47 %, respectively. MRI showed seven false-positive bone lesions after successful chemotherapy. PET showed five false-negative small bone lesions, one false-negative lesion of the skull and three false-negative findings for intracerebral involvement. PET showed one false-positive lesion in the lymphoid tissue of the head and neck region and two false-positive bone lesions after treatment. Combined PET/MR analysis decreased the number of false-negative findings on primary staging, whereas no advantage over PET alone was seen in terms of false-positive or false-negative results on follow-up. CONCLUSION: Our retrospective analysis suggests a pivotal role of (18)F-FDG PET in lesion follow-up due to a lower number of false-positive findings after chemotherapy. MRI showed a higher sensitivity and is indispensable for primary staging, evaluation of brain involvement and biopsy planning. Combined MRI/PET analysis improved sensitivity by decreasing the false-negative rate during primary staging indicating a future role of simultaneous whole-body PET/MRI for primary investigation of paediatric histiocytosis.

¹²³I-MIBG scintigraphy/SPECT versus ¹8F-FDG PET in paediatric neuroblastoma.

PURPOSE: To analyse different uptake patterns in (123)I-MIBG scintigraphy/SPECT imaging and (18)F-FDG PET in paediatric neuroblastoma patients. METHODS: We compared 23 (123)I-MIBG scintigraphy scans and 23 (18)F-FDG PET scans (mean interval 10 days) in 19 patients with a suspected neuroblastic tumour (16 neuroblastoma, 1 ganglioneuroblastoma, 1 ganglioneuroma and 1 opsomyoclonus syndrome). SPECT images of the abdomen or other tumour-affected regions were available in all patients. Indications for (18)F-FDG PET were a (123)I-MIBG-negative tumour, a discrepancy in (123)I-MIBG uptake compared to the morphological imaging or imaging results inconsistent with clinical findings. A lesion was found by (123)I-MIBG scintigraphy and/or (18)F-FDG PET and/or morphological imaging. RESULTS: A total of 58 suspicious lesions (mean lesion diameter 3.8 cm) were evaluated and 18 were confirmed by histology and 40 by clinical follow-up. The sensitivities of (123)I-MIBG scintigraphy and (18)F-FDG PET were 50% and 78% and the specificities were 75% and 92%, respectively. False-positive results (three (123)I-MIBG scintigraphy, one (18)F-FDG PET) were due to physiological uptake or posttherapy changes. False-negative results (23 (123)I-MIBG scintigraphy, 10 (18)F-FDG PET) were due to low uptake and small lesion size. Combined (123)I-MIBG scintigraphy/(18)F-FDG PET imaging showed the highest sensitivity of 85%. In 34 lesions the (123)I-MIBG scintigraphy and morphological imaging findings were discrepant. (18)F-FDG PET correctly identified 32 of the discrepant findings. Two bone/bone marrow metastases were missed by (18)F-FDG PET. CONCLUSION: (123)I-MIBG scintigraphy and (18)F-FDG PET showed noticeable differences in their uptake patterns. (18)F-FDG PET was more sensitive and specific for the detection of neuroblastoma lesions. Our findings suggest that a (18)F-FDG PET scan may be useful in the event of discrepant or inconclusive findings on (123)I-MIBG scintigraphy/SPECT and morphological imaging.

PET/CT in malignant melanoma: contrast-enhanced CT versus plain low-dose CT.

PURPOSE: The aim of this study was to evaluate the diagnostic value of contrast-enhanced CT (CECT) versus non-enhanced low-dose CT (NECT) in the staging of advanced malignant melanoma with (18)F-fluordeoxyglucose (FDG) positron emission tomography (PET)/CT. METHODS: In total, 50 (18)F-FDG PET/CT examinations were performed in 50 patients with metastasized melanoma. For attenuation correction, whole-body NECT was performed followed by diagnostic CECT with contrast agent. For the whole-body PET, (18)F-FDG was applied. Criteria for evaluation were signs of vital tumour tissue (extent of lesions, contrast enhancement, maximum standardized uptake value >2.5). Findings suspicious for melanoma were considered lesions. NECT, CECT and (18)F-FDG PET were evaluated separately, followed by combined analysis of PET/NECT and PET/CECT. Findings were verified histologically and/or by follow-up (>6 months). RESULTS: Overall, 232 lesions were analysed, and 151 proved to be metastases. The sensitivity of NECT, CECT, PET, PET/NECT and PET/CECT was 62, 85, 90, 97 and 100%, and specificity was 52, 63, 88, 93 and 93%, respectively. Compared to CECT, NECT obtained additional false-negative results: lymph node (n = 19) and liver/spleen metastases (n = 9). Misinterpreted physiological structures mainly caused additional false-positive findings (n = 17). In combined analysis of PET/NECT, six false-positive [other tumours (n = 2), inflammatory lymph nodes (n = 2), inflammatory lung lesion (n = 1), blood vessel (n = 1)] and five false-negative findings [liver (n = 3), spleen (n = 1), lymph node metastases (n = 1)] remained. On PET/CECT, six false-positive [inflammatory lymph nodes (n = 3), other tumours (n = 2), inflammatory lung lesion (n = 1)] and no false-negative findings occurred. However, additional false findings on PET/NECT (6 of 232) did not change staging compared to PET/CECT. CONCLUSION: Our results indicate that it is justified to perform PET/NECT instead of PET/CECT for melanoma staging.