[Imaging of neuroendocrine tumors of the gastrointestinal tract : Value of (hybrid) imaging diagnostics in radiology]. / Bildgebung von neuroendokrinen Tumoren des Gastrointestinaltrakts : Bedeutung der (hybriden) bildgebenden Diagnostik in der Radiologie.

CLINICAL/METHODICAL ISSUE: Neuroendocrine tumors (NET) represent a heterogeneous group of rare tumors that predominantly arise in the gastrointestinal tract. At the time of initial diagnosis, the NET has already spread locoregionally in about half of the patients, and 27% of patients have already developed distant metastases. Since this plays a crucial role in therapy planning, accurate diagnostic imaging is important. STANDARD RADIOLOGICAL METHODS: Due to its high temporal and spatial resolution (multiphasic including arterial phase), computed tomography (CT) plays a decisive role in primary staging and follow-up care, while magnetic resonance imaging (MRI) with its excellent soft tissue contrast offers advantages in the assessment of parenchymal organs in the upper abdomen. METHODICAL INNOVATIONS: Somatostatin receptor (SSR) positron emission tomography (PET) provides additional functional information that not only helps to detect the primary tumor and distant metastases, but also has a significant influence on therapeutic management in a theranostic approach. PERFORMANCE: Hybrid imaging using SSR-PET/CT has proven to be particularly effective in the detection of NET. Compared to conventional imaging, it provides additional information in 68% of patients, which has a significant impact on clinical management. ACHIEVEMENTS: Imaging of NET requires the combined use of various methods such as ultrasound, CT, MRI, and PET/CT to enable accurate diagnosis and effective treatment planning. PRACTICAL RECOMMENDATIONS: SSR-PET/CT is a valuable tool for the accurate staging of neuroendocrine tumors of the gastrointestinal tract, especially with small metastases, while MRI with hepatocyte-specific contrast agent and diffusion-weighted imaging is useful for the specific assessment of liver metastases.

Diagnostic accuracy of SSR-PET/CT compared to histopathology in the identification of liver metastases from well-differentiated neuroendocrine tumors.

BACKGROUND: Histopathology is the reference standard for diagnosing liver metastases of neuroendocrine tumors (NETs). Somatostatin receptor-positron emission tomography / computed tomography (SSR-PET/CT) has emerged as a promising non-invasive imaging modality for staging NETs. We aimed to assess the diagnostic accuracy of SSR-PET/CT in the identification of liver metastases in patients with proven NETs compared to histopathology. METHODS: Histopathologic reports of 139 resected or biopsied liver lesions of patients with known NET were correlated with matching SSR-PET/CTs and the positive/negative predictive value (PPV/NPV), sensitivity, specificity, and diagnostic accuracy of SSR-PET/CT were evaluated. PET/CT reading was performed by one expert reader blinded to histopathology and clinical data. RESULTS: 133 of 139 (95.7%) liver lesions showed malignant SSR-uptake in PET/CT while initial histopathology reported on 'liver metastases of NET´ in 127 (91.4%) cases, giving a PPV of 91.0%. Re-biopsy of the initially histopathologically negative lesions (reference standard) nevertheless diagnosed 'liver metastases of NET' in 6 cases, improving the PPV of PET/CT to 95.5%. Reasons for initial false-negative histopathology were inadequate sampling in the sense of non-target biopsies. The 6 (4.3%) SSR-negative lesions were all G2 NETs with a Ki-67 between 2-15%. CONCLUSION: SSR-PET/CT is a highly accurate imaging modality for the diagnosis of liver metastases in patients with proven NETs. However, we found that due to the well-known tumor heterogeneity of NETs, specifically in G2 NETs approximately 4-5% are SSR-negative and may require additional imaging with [18F]FDG PET/CT.

[Gastroenteropancreatic endocrine tumors]. / Gastroenteropankreatische endokrine Tumoren.

CLINICAL/METHODICAL ISSUE: Gastroenteropancreatic neuroendocrine tumors (GEP-NET) are a rare, heterogeneous group of neoplasms. Only 2% of gastrointestinal tumors belong to the group of neuroendocrine neoplasms. STANDARD RADIOLOGICAL METHODS: A wide spectrum of diagnostic imaging modalities is available: apart from ultrasound not only computed tomography (CT) but also magnetic resonance imaging (MRI) and positron emission tomography CT (PET-CT) play an important role in detection and staging of GEP-NETs. METHODICAL INNOVATIONS: The PET-CT technique with somatostatin analogues is used for staging as well as for evaluation and monitoring of treatment with peptide radionuclide radiation therapy. PERFORMANCE: According to the literature NETs of the small bowel with a size over 3 cm can be detected with a sensitivity of 84.7% and a specificity of 96.6% using CT enteroclysis and MR enteroclysis provides the detection of NETs of the small bowel in 93.3% of cases. 'The sensitivity of MRI in detection of pancreatic NETs is between 74% and 100% and is, therefore, higher than CT. Detection of small primary tumors is carried out using PET-CT and seems to be the most sensitive imaging modality to identify the exact location. On the other hand MRI has to be regarded as the best imaging modality for detection of liver metastases compared to CT and PET-CT. ACHIEVEMENTS: The role of diagnostic imaging is to identify the exact location of the primary tumor and possible metastases, to define an appropriate therapy and to monitor treatment effects; however, the choice of the most appropriate diagnostic imaging modality varies depending on the location and type of the primary tumor. PRACTICAL RECOMMENDATIONS: The GEP-NETs are predominantly well-vascularized; therefore, dual-phase CT/MR imaging with the arterial and venous phases after contrast media injection is mandatory for detection and localization of primary tumors and metastases. For whole body staging CT and PET-CT should be performed.

Role of diffusion-weighted MRI in differentiation of hepatic abscesses from non-infected fluid collections.

AIM: To evaluate the role of diffusion-weighted magnetic resonance imaging (DW-MRI) in the differentiation of hepatic abscesses from non-infected fluid collections. MATERIALS AND METHODS: In this retrospective study, 22 hepatic abscesses and 27 non-infected hepatic fluid collections were examined in 27 patients who underwent abdominal MRI including DW-MRI. Two independent observers reviewed T2-weighted + DW-MRI and T2-weighted + contrast-enhanced T1-weighted (CET1W) images in two sessions. Detection rates and confidence levels were calculated and compared using McNemar's and Wilcoxon's signed rank tests, respectively. Apparent diffusion coefficient (ADC) values of abscesses and non-infected fluid collections were compared using the t-test. Receiver operating characteristic (ROC) curves were constructed. RESULTS: There was no statistically significant difference in the accuracy of detecting abscesses using T2-weighted + DW-MRI (both observers: 21/22, 95.5%) versus T2-weighted + CET1W images (observer 1: 21/22, 95.5%; observer 2: 22/22, 100%; p < 0.01). Mean ADC values were significantly lower with abscesses versus non-infected fluid collections (0.83 ± 0.24 versus 2.25 ± 0.61 × 10(-3) mm(2)/s; p < 0.001). With ROC analysis there was good discrimination of abscess from non-infected fluid collections at a threshold ADC value of 1.36 × 10(-3) mm(2)/s. CONCLUSION: DW-MRI allows qualitative and quantitative differentiation of abscesses from non-infected fluid collections in the liver.

DW-MRI of liver lesions: can a single ADC-value represent the entire lesion?

AIM: To evaluate whether focal liver lesions (FLLs) exhibit a homogeneous appearance on apparent diffusion coefficient (ADC) maps and whether there is inter-section variation in the calculated ADC values of FLLs (inter-section range). MATERIALS AND METHODS: Eighty-eight patients with 128 FLLs (70 benign, 58 malignant) who underwent abdominal magnetic resonance imaging (MRI) including diffusion-weighted (DW)-MRI were included. Two observers evaluated variation of signal intensity of each FLL within each ADC map image (intra-section) and among different ADC map images through the lesion (inter-section). ADC values of each FLL and neighbouring liver parenchyma were measured on all sections. The inter-section range of FLLs was compared with the neighbouring liver parenchyma. RESULTS: Intra-section inhomogeneity was noted in 39.8% (97/244 sections) and 38.9% (95/244) of benign lesions, and 61% (114/187 sections) and 61.5% (115/187) of malignant lesions, by observer 1 and observer 2, respectively. Inter-section inhomogeneity was noted in 25.7% (18/70) and 27.1% (19/70) of benign lesions, and 51.7% (30/58) and 50% (29/58) of malignant lesions, by observer 1 and observer 2, respectively. The inter-section range for both benign (0.28 × 10(-3) mm(2)/s) and malignant (0.25 × 10(-3) mm(2)/s) FLLs were significantly greater than that of liver parenchyma surrounding benign (0.16 × 10(-3) mm(2)/s, p < 0.001) and malignant (0.14 × 10(-3) mm(2)/s, p = 0.01) FLLs. CONCLUSION: Due to intra-/inter-section variations in ADC values of benign and malignant FLLs, a single ADC value may not reliably represent the entire lesion.

Detection of underlying malignancy in patients with paraneoplastic neurological syndromes: comparison of 18F-FDG PET/CT and contrast-enhanced CT.

PURPOSE: To determine the value of combined (18)F-FDG PET/CT with diagnostic contrast-enhanced CT (CECT) in detecting primary malignancies and metastases in patients with paraneoplastic neurological syndromes (PNS) and to compare this with CECT alone. METHODS: PET/CT scans from 66 patients with PNS were retrospectively evaluated. Two blinded readers initially reviewed the CECT portion of each PET/CT scan. In a second session 3 months later, the readers analysed the combined PET/CT scans. Findings on each study were assessed using a four-point-scale (1 normal/benign; 2 inconclusive, further diagnostic work-up may be necessary; 3 malignant; 4 inflammatory). Sensitivity and specificity for malignant findings were calculated for PET/CT and CECT. Interreader agreement was determined by calculating Cohen's kappa. Pooled data from clinical follow-up (including histopathology and follow-up imaging, median follow-up 20.0 months) served as the reference gold standard. RESULTS: Both readers classified 12 findings in ten patients (15%) as malignant on the PET/CT scans (two patients had two primary tumours). One such imaging finding (suspected thymic cancer) was false-positive (i.e. benign histology). The most common tumours were bronchial carcinoma (n = 3), lymph node metastases of gynaecological tumours (n = 3) and tonsillar carcinoma (n = 2). Three of 12 findings (25%) were not detected by CECT alone (cervical carcinoma, lymph node metastasis and tonsillar carcinoma). In a per-patient analysis, sensitivity and specificity for malignant findings were 100% and 90% for PET/CT and 78% and 88% for CECT. In 24% (reader 1) and 21% (reader 2) of the patients, the PET/CT findings were inconclusive. Of these findings, 57% (reader 1) and 56% (reader 2) were only diagnosed with PET (e.g. focal FDG uptake of the thyroid, gastrointestinal tract and ovaries). On follow-up, none of these findings corresponded to malignancy. Overall agreement between the two readers was excellent with a Cohen's kappa of 0.95 ± 0.04 (p < 0.001) for PET/CT and 0.97 ± 0.03 (p < 0.001) for CECT alone. CONCLUSION: In this cohort of patients with PNS, PET/CT exhibited improved detection of underlying malignancy versus CECT alone. While hybrid imaging produces a greater number of inconclusive findings, sensitivity is increased for the detection of head and neck and gynaecological malignancies as well as metastatic lymph node involvement.

[Diffusion-weighted magnetic resonance imaging of the abdomen]. / Diffusionsgewichtete Magnetresonanztomographie des Abdomens.

Diffusion-weighted magnetic resonance imaging (DW-MRI) provides qualitative and quantitative information of tissue cellularity and the integrity of cellular membranes. Since DW-MRI can be performed without ionizing radiation exposure and contrast media application, DW-MRI is a particularly attractive tool for patients with allergies for gadolinium-based contrast agents or renal failure. Recent technical developments have made DW-MRI a robust and feasible technique for abdominal imaging. DW-MRI provides information on the detection and characterization of focal liver lesions and can also visualize treatment effects and early changes in chronic liver disease. In addition DW-MRI is a promising tool for the detection of inflammatory changes in patients with Crohn's disease.

[Characteristic imaging features of carcinoid tumors of the small bowel in MR enteroclysis]. / Morphologisches Erscheinungsbild neuroendokriner Tumoren des Dünndarms im MR-Enteroklysma.

PURPOSE: To determine the value of MR enteroclysis (MRE) in the localization and characterization of primary carcinoid tumors of the small bowel and to describe typical imaging features. MATERIAL AND METHODS: Twenty patients with suspicion of primary small bowel carcinoid tumors (pCT) were recruited to undergo MRE following nasojejunal intubation and small bowel filling with 2.5 l of 0.5% methylcellulose solution under MR fluoroscopic guidance. MRE was performed on a 1.5 T MR scanner including T2w SSFSE, SSFP and contrast enhanced T1w GRE sequences with fat saturation. Fifteen patients, who subsequently had surgery for resection of their pCT, were retrospectively included in the study. All MRE were analyzed as for the presence, location, number, size, multiplicity and morphologic appearance of the pCT by two board certified radiologists in consensus. The conspicuity of the tumors was rated for each sequence type separately, according to a 4-point rating scale. Signal intensity measurements were performed in tumor and muscle. The presence of desmoplastic reaction, vascular involvement and lymph node metastases was also analyzed. RESULTS: pCT were correctly identified and localized in 14/15 patients. Due to their hyperenhancement tumors was best detected on contrast-enhanced T1w fat saturated GRE sequences. SSFSE was clearly inferior with the tumors being either hyperintense or isointense to muscle. pCT appeared as nodular intraluminal masses in 40% of the cases, as focal wall thickening in 33.3% and in 20% with both. Mean size was 25 (7-46 mm) with a tendency to smaller size for ileal tumors. MRE failed to depict superficial micronodular peritoneal spread in one patient. Desmoplastic reaction was observed in 73.3% of the cases with mesenteric masses exhibiting lower signal than the pCT due to fibrotic changes. CONCLUSION: MRE is a valuable method for the detection and localization of primary carcinoid tumors, provided that appropriate bowel distension is achieved. Various characteristic morphologic features could be identified which may contribute to characterize pCT and their loco-regional metastases.