Whole-body (11)C-5-hydroxytryptophan positron emission tomography as a universal imaging technique for neuroendocrine tumors: comparison with somatostatin receptor scintigraphy and computed tomography

Differential diagnosis of Cushing's syndrome

The differential diagnosis of Cushing's syndrome requires careful multidisciplinary interaction with a number of specialities, co-ordinated through endocrine centres with good experience of this condition. It is essential that the diagnosis of Cushing's syndrome be fully established before differential diagnosis is attempted. The endocrinologist needs to be aware of the pitfalls and advantages of the tests in use. We discuss the approach to the differential diagnosis of this challenging condition.

Pitfalls in the diagnosis of Cushing's syndrome

Among endocrine disorders, Cushing's syndrome (CS) is certainly one of the most challenging to endocrinologists due to the difficulties that often appear during investigation. The diagnosis of CS involves two steps: confirmation of hypercortisolism and determination of its etiology. Biochemical confirmation of the hypercortisolaemic state must be established before any attempt at differential diagnosis. Failure to do so will result in misdiagnosis, inappropriate treatment, and poor management. It should also be kept in mind that hypercortisolism may occur in some patients with depression, alcoholism, anorexia nervosa, generalized resistance to glucocorticoids, and in late pregnancy. Moreover, exogenous or iatrogenic hypercortisolism should always be excluded. The three most useful tests to confirm hypercortisolism are the measurement of 24-h urinary free cortisol levels, low-dose dexamethasone-suppression tests, and determination of midnight serum cortisol or late-night salivary cortisol. However, none of these tests is perfect, each one has different sensitivities and specificities, and several are usually needed to provide a better diagnostic accuracy. The greatest challenge in the investigation of CS involves the differentiation between Cushing's disease and ectopic ACTH syndrome. This task requires the measurement of plasma ACTH levels, non-invasive dynamic tests (high-dose dexamethasone suppression test and stimulation tests with CRH or desmopressin), and imaging studies. None of these tests had 100% specificity and their use in combination is usually necessary. Bilateral inferior petrosal sinus sampling is mainly indicated when non-invasive tests do not allow a diagnostic definition. In the present paper, the most important pitfalls in the investigation of CS are reviewed.

[Endocrine tumors of the pancreas (EPTs) in multiple endocrine neoplasia (MEN1): up-date on prognostic factors, diagnostic procedures and treatment]

Endocrine pancreatic tumors (EPTs) are uncommon tumors, representing 1-2% of all pancreatic neoplasms. They are categorized on the basis of their clinical features into functioning and non-functioning tumors. EPTs may be part of the multiple endocrine neoplasia type 1 (MEN 1), an autosomal dominant syndrome due to inactivating germline mutation of the menin gene. Somatic mutations of menin are present in about 20% of sporadic neoplasms, particularly gastrinomas and insulinomas. 30-75% of patients with MEN1 have EPTs. The most prevalent are the gastrinomas (20-60%), then the insulinomas (5-10%), the glucagonamas and VIPomas (6-10%), whereas the nonfunctioning EPTs are present in 20-40% of patients. The most important biochemical screening marker for EPTs is chromogranin A, as it increases in 50-80% of patients. The most important negative prognostic factors are the presence of metastases, the gross invasion of adjacent organs, the angioinvasion, the perineural invasion and an immunopositivity for Ki-67 > 2%. Among the different imaging techniques, echoendoscopy, computed tomography (CT) and magnetic resonance imaging (MRI) are indicated for the detection of the primary tumor, but (III)In-octreotide scintigraphy has the highest sensitivity for detecting metastases. The choice of treatment is still debated and is different when the tumor occurs as a part of the MEN syndrome. The surgical treatment is the first choice for insulinomas and is more controversial for gastrinomas. The medical treatment includes somatostatin analogues (SA), chemotherapy and interferon-alpha (IFN-alpha). SA seem to improve the symptoms and have an antiproliferative effect, the most striking effect being seen in patients with VIPomas. Chemotherapy, which is generally proposed as a combination of streptozotocin (STZ) and 5-fluorouracil (5-FU) or doxorubicin, is indicated when the tumors tend to grow. Interferon-alpha (IFN-alpha) stimulates the immune system, blocks the tumor cells in the G1/S-phase of the cell cycle, inhibits protein and hormone synthesis and inhibits angionenesis. Treatment with IFN has been shown to produce symptomatic response in 40-60% of patients, a biochemical response in 30-60% and tumor shrinkage in 10-15%.

Radio-guided surgery in neuroendocrine tumors

The majority of Neuroendocrine tumors (NET) express somatostatin (SS) receptors, and thus can be successfully targeted with radiolabeled SS analogs in vivo. Somatostatin receptor scintigraphy (SRS) with (111)In-DTPA Octreotide is the main imaging technique for evaluation of NETs. Radio-guided surgery for NETs, therefore, primarily utilizes (111)In-DTPA Octreotide tumor localization mechanism and kinetics. Somatostatin analog radiopharmacy continues to evolve to include the development of more selective and higher affinity analogs and PET tracers. These changes are expected to open new venues for radio-guided surgery technology.

Neuroblastoma and other neuroendocrine tumors

Neuroblastoma is the most common extracranial solid tumor of childhood. It commonly presents in children younger than 2 years of age, with 90% being younger than 5 years of age. There is marked variability in clinical behavior ranging from spontaneous regression or differentiation into benign tumors to rapid and progressive fatal disease. Approximately 50% of patients will have metastases at presentation. The management is dependent on age, stage of disease, and biological and biochemical markers. Nuclear medicine plays an important role in the initial staging, as a prognostic indicator, for assessment of response to treatment, and also in therapy. The most common nuclear medicine diagnostic studies are (99m)Tc-disphosphonate bone scintigraphy and (123)I-MIBG (metaiodobenzylguanidine) scintigraphy. Bone scintigraphy has been the main investigational modality to diagnose skeletal metastases. Whole body imaging with (123)I-MIBG has become the preferred diagnostic test because this agent accumulates in neuroblastoma in 90% to 95% of cases and will accumulate in the primary tumor and metastases particularly in bone, bone marrow, lymph nodes, and soft tissues. MIBG can be used to assess therapy response and is a significant prognostic indicator. Other diagnostic techniques include positron emission tomography (PET)/computed tomography, mainly using (18)F-fluorodeoxyglucose. Other more experimental PET agents, as well as radiolabeled antibodies and octreotide, also are being investigated. Therapy has mainly focused on palliation and has been used alone or in combination with chemotherapy in high-risk refractory or relapsed patients. Major attention is being placed on stratification of patients to try and reduce the side effects associated with intensive megatherapy in the low to intermediate risk patients. Neuroendocrine tumors (NETs) are rare in childhood, but nuclear medicine techniques, mainly using MIBG and somatostatin receptor agents, have a role in diagnosis, staging, and a limited role in therapy. Newer radiopharmaceuticals, including PET agents, are being evaluated for the assessment of NET. Nuclear medicine techniques play a major role in the management of neuroblastoma and NET.

Radio-guided surgery with the use of [99mTc-EDDA/HYNIC]octreotate in intra-operative detection of neuroendocrine tumours of the gastrointestinal tract

PURPOSE

Radio-guided surgery (RGS) is an intra-operative localising technique which enables identification of tissue "marked" by a specific radiotracer injected before surgery. It is mainly used for sentinel node mapping and for detection of parathyroid adenomas and other tumours, including neuroendocrine tumours of the gastrointestinal tract (GEP-NET). The aim of this study was to determine whether intra-operative radio-detection with the use of [(99m)Tc-EDDA/HYNIC]octreotate, a new somatostatin analogue, is able to reveal an unknown primary and secondary sites, thereby improving surgical treatment and the final outcome of GEP-NET.

METHODS

The study group included nine patients with suspected GEP-NET (four carcinoids, five pancreatic NET) localised with somatostatin receptor scintigraphy (with [(99m)Tc-EDDA/HYNIC]octreotate), who had negative results on other pre-operative imaging tests. At surgery, suspected tumours were measured in situ and ex vivo and precise exploration of the abdominal cavity was performed with the intra-operative scintillation detector (Navigator).

RESULTS

Intra-operative gamma counting localised three carcinoids. In one patient SRS was false positive (owing to inflammatory infiltration). Compared with SRS, RGS revealed additional lymph node metastases in one case. RGS resulted in successful localisation of all pancreatic NET (the smallest lesion was 8 mm in diameter).

CONCLUSION

[(99m)Tc-EDDA/HYNIC]octreotate SRS followed by RGS is a promising technique to improve the rate of detection and efficacy of treatment of GEP-NET, especially in the presence of occult endocrine tumours. The imaging properties of [(99m)Tc-EDDA/HYNIC]octreotate and the 1-day imaging protocol offer opportunities for more widespread application of this tracer followed by RGS in oncology.

Anatomic and functional imaging of metastatic carcinoid tumors

Carcinoid tumors are a fascinating group of neuroendocrine neoplasms that develop either sporadically or as part of an inheritable syndrome. Many tumors arise in the bronchopulmonary or gastrointestinal tract, but a neuroendocrine tumor can arise in almost any organ. The tumors have varied malignant potential depending on the site of their origin, and the clinical manifestations often are nonspecific. Metastases may be present at the time of diagnosis, which often occurs at a late stage of the disease. Imaging plays a pivotal role in the localization and staging of neuroendocrine tumors and in monitoring the treatment response. Imaging is often challenging, and a combination of anatomic and functional techniques is usually required, depending on the tumor type and location. Techniques include ultrasonography, barium studies, endoscopy, computed tomography, magnetic resonance imaging, somatostatin receptor scintigraphy, iobenguane scintigraphy, and, in select cases, positron emission tomography. Coregistration of structural and functional images is often of incremental value for accurate localization of the primary tumor and any meta-static disease. Radiologists must understand the contribution of each imaging modality in the assessment of different neuroendocrine tumors. In addition, knowledge of the optimal technique for each radiologic and radionuclide imaging examination is essential. Familiarity with the protean imaging appearances of both primary and metastatic disease is essential for accurate staging, treatment monitoring, and surveillance. Finally, an understanding of the wide variety of treatment options for patients with carcinoid tumors is vital for optimal management.

Bronchial typical carcinoid tumors

The current WHO classification of lung tumors recognizes bronchial typical carcinoid as low-grade neuroendocrine tumors. These tumors grow slowly but can metastasize to regional nodes (4 to 20%) and more rarely to extrathoracic sites. Symptoms are usually related to local compression and obstruction of the bronchial tree. Paraneoplastic syndrome can be present (carcinoid syndrome, Cushing's syndrome, acromegaly). Preoperative diagnosis is usually obtained with bronchoscopic biopsy. Computed tomography and somatostatin receptor scintigraphy are useful in the preoperative staging. Only selected cases can be treated endoscopically with laser resection. The complete surgical resection remains the only therapy with curative intent in the majority of patients. Parenchyma-sparing resections are indicated whenever possible. Overall survival after surgery is excellent (5-year rate, 87 to 100%) with low recurrence rate (2 to 11%). N-status and type of resection seem not to affect prognosis. Local relapse can be treated successfully with surgery, whereas distant metastases have a poor prognosis even after chemotherapy.

Nuclear imaging of neuroendocrine tumours

The diagnosis of neuroendocrine tumours (NETs) and monitoring of therapy in many patients relies mainly on morphological imaging techniques such as computed tomography (CT), ultrasound (US) and magnetic resonance imaging (MRI). However, functional imaging modalities--such as somatostatin receptor scintigraphy (SRS)--have great impact on patient management by providing tools for better staging of the disease, visualization of occult tumour, and evaluation of eligibility for somatostatin analogue treatment. Positron emission tomography (PET) using (18)F-fluoro-deoxy-glucose (FDG) is a powerful functional modality for oncological imaging. Unfortunately, FDG is not accumulated in NETs except in the case of dedifferentiated tumours and tumours with high proliferative activity. Based on the concept of amine precursor uptake and decarboxylation (APUD), the (18)F- and (11)C-labelled amine precursors L-dihydroxyphenylalanine and 5-hydroxy-L-tryptophan (5-HTP) have been utilized for PET imaging of NETs. In comparative studies of patients with a variety of NETs, (11)C5-HTP-PET proved better than CT and SRS by visualizing additional small lesions. With carbidopa premedication orally before (11)C5-HTP-PET examination the tumour uptake could be increased and the urinary radioactivity concentration considerably reduced. This concept may also be applied to (18)F-L-DOPA-PET, a method which in a limited number of studies has gained additional diagnostic information in NET patients compared to SRS and morphological imaging. (68)Ga is available from an in-house generator and has been utilized for labelling of somatostatin analogues for PET imaging of NETs with promising results in a small number of patients. However, SRS is an established functional imaging method for patients with NETs, whereas the role for PET in the clinical routine needs further evaluation in comparative studies in larger groups of patients.

Functioning and nonfunctioning neuroendocrine tumors of the pancreas

PURPOSE OF REVIEW

Neuroendocrine tumors of the pancreas are a small subgroup of tumors characterized by a variety of biological behaviors. Recent changes in their classification should help better define the prognosis of this diverse group of tumors. With recent advances in diagnosis and staging, the treatment options for all neuroendocrine tumors have evolved. Presented here is a review of the current-day knowledge for neuroendocrine tumors of the pancreas.

RECENT FINDINGS

A consensus by leading experts in the neuroendocrine tumors field has proposed an algorithm for the diagnosis, treatment and follow-up of these rare tumors. Surgical resection remains the first-line therapy. Alternative forms of cytoreduction such as radiofrequency ablation and embolization, have increased the ability of the surgeon to debulk these tumors, resulting in improved survival and better palliation. Contrary to adenocarcinoma of the pancreas, hormonal and biotherapy offer unique treatment strategies for these rare tumors. Very recent developments utilizing radionuclide therapy hold promise for not only palliation, but may prove to be a beneficial form of adjuvant therapy.

SUMMARY

Presented here is a summary of the recent literature on the diagnosis and treatment of neuroendocrine tumors of the pancreas.

Imaging of neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare neoplasms, which are characterized by the presence of neuroamine uptake mechanisms and/or peptide receptors at the cell membrane and these features constitute the basis of the clinical use of specific radiolabeled ligands, both for imaging and therapy. Radiolabeled metaiodobenzylguanidine (MIBG) was the first radiopharmaceutical used to specifically depict and localize catecholamine-secreting tumors (pheochromocytomas, paragangliomas, and neuroblastomas) and is still regarded as a first-choice imaging technique for diagnosis and follow-up; in patients with malignant disease, MIBG scintigraphy is an essential step to select patients for (131)I-MIBG therapy. Scintigraphy with (111)In- or (99m)Tc-labeled somatostatin analogs has become the main imaging technique for NETs, particularly those expressing a high density of somatostatin receptors, such as gastroenteropancreatic tumors; this procedure is used routinely for localizing the primary tumor, evaluating disease extension, monitoring the effect of treatment and for selecting patients for radioreceptor therapy. Since the recent development of hybrid machines, it has been possible to obtain images that simultaneously hold both anatomic (computed tomography [CT]) and functional (single-photon emission computed tomography [SPECT] or positron emission tomography [PET]) information, with great impact on diagnostic accuracy. Significant improvements have been made during the past few years with the development of highly specific radiopharmaceuticals for PET studies that reflect the different metabolic pathways of NETs, such as glucose metabolism ((18)F-fluorodeoxyglucose), the uptake of hormone precursors ((11)C-5-hydroxytryptophan, (11)C- or (18)F-dihydroxyphenylalanine, (18)F-fluorodopamine), the expression of receptors ((68)Ga-labeled somatostatin analogs), as well as the synthesis, storage, and release of hormones ((11)C-hydroxyephedrine and others). Among these radiopharmaceuticals, (68)Ga-labeled somatostatin analogs are increasingly used in specialized centers in Europe for PET and PET/CT imaging and show very promising results with high diagnostic sensitivity. New somatostatin analogs with different receptor affinity as well as other peptides are currently under investigation and will further improve our diagnostic and therapeutic capabilities in the future.

Large bowel carcinoid tumors

PURPOSE OF REVIEW

Gastrointestinal carcinoids comprise 90% of all carcinoid tumors and all carcinoids have malignant potential. This review focuses on the morphology, prognosis, detection and treatment for appendiceal, colonic and rectal carcinoids.

RECENT FINDINGS

Computed tomography exists as an initial examination for the primary carcinoid tumor as well as for metastases. There have, however, been recent developments of newer and more accurate modalities. Octreotide scanning has a sensitivity of primary tumor detection of 90%; additionally, I- or I-meta-iodobenzylguanidine scanning and tracer-specific positron emission tomographic scans have demonstrated encouraging results. Further advancements in treatment with tumor-targeted therapy and biochemical evaluation of carcinoids have shown promise.

SUMMARY

The recent progress with scintigraphic and radiologic modalities has provided better means for diagnosis of primary and metastatic carcinoid tumors. These newly discovered diagnostic modalities have been more encouraging than the recent treatment approaches that have been studied with regard to metastatic carcinoids. While surgery remains the mainstay of treatment of nonmetastatic carcinoid, there have been studies for various medical treatments of metastatic disease. Unfortunately, there have been disappointing results with regard to improvement of tumor response and patient survival, but a foundation has been established for future trials employing alternative agents and exploration of combination therapies.

Review article: Pathogenesis and management of gastric carcinoid tumours

BACKGROUND

Gastric carcinoid tumours are rare, but are increasing in incidence.

AIM

To discuss tumour pathogenesis and outline current approaches to patient management.

METHODS

Review of published articles following a Pubmed search.

RESULTS

Although interest in gastric carcinoids has increased since it was recognized that they are associated with achlorhydria, to date there is no definite evidence that humans taking long-term acid suppressing medication are at increased risk. Type I tumours are associated with autoimmune atrophic gastritis and hypergastrinaemia, type II are associated with Zollinger-Ellison syndrome, multiple endocrine neoplasia-1 and hypergastrinaemia and sporadic type III carcinoids are gastrin-independent and carry the worst prognosis. Careful investigation of these patients is required, particularly to identify the tumour type, the source of hypergastrinaemia and the presence of metastases. Treatment can be directed at the source of hypergastrinaemia if type I or II tumours are still gastrin responsive and not growing autonomously. Type III tumours should be treated surgically.

CONCLUSIONS

Advances in our understanding of the pathogenesis of gastric carcinoids have led to recent improvements in investigation and management. Challenges remain in identifying the genetic and environmental factors, in addition to hypergastrinaemia, that are responsible for tumour development in susceptible patients.

Familial paragangliomas

Paragangliomas are rare tumours of the autonomic nervous system and occur in sporadic and hereditary forms. They are usually benign and have a low mortality. However, they cause significant morbidity related to their mass effect. Genetic predisposition can occur within the familial tumour syndromes multiple endocrine neoplasia type 2 (MEN 2), von Hippel-Lindau (VHL) and neurofibromatosis type 1 (NF-1), or be due to mutations in genes specific to the development of paraganglioma only. Compared to sporadic forms, familial paragangliomas tend to present at a younger age and at multiple sites. Tumours should be diagnosed and resected as early as possible, as it has been shown that morbidity is related to tumour size. This article gives an overview of the current literature on the origin of the different forms of paragangliomas, DNA diagnosis, as well as biochemical and radiological screening guidelines.

Staging of carcinoid tumours with 18F-DOPA PET: a prospective, diagnostic accuracy study

BACKGROUND

To assess individual treatment options for patients with carcinoid tumours, accurate knowledge of tumour localisation is essential. We aimed to test the diagnostic sensitivity of 6-[fluoride-18]fluoro-levodopa ((18)F-DOPA PET), compared with conventional imaging methods, in patients with carcinoid tumours.

METHODS

In a prospective, single-centre, diagnostic accuracy study, (18)F-DOPA PET with carbidopa pretreatment was compared with somatostatin-receptor scintigraphy (SRS), CT, and combined SRS and CT in 53 patients with a metastatic carcinoid tumour. The performance of all imaging methods was analysed for individual patients, for eight body regions, and for the detection of individual lesions. PET and CT images were fused to improve localisation. To produce a composite reference standard, we used cytological and histological findings; all imaging tests, including secondary assessments for newly found lesions; follow-up; and biochemical data. Sensitivities were calculated and compared.

FINDINGS

In patient-based analysis, we recorded sensitivities of 100% (95% CI 93-100) for (18)F-DOPA-PET, 92% (82-98) for SRS, 87% (75-95) for CT, and 96% (87-100) for combined SRS and CT (p=0.45 for (18)F-DOPA PET vs combined SRS and CT). However, (18)F-DOPA PET detected more lesions, more positive regions, and more lesions per region than combined SRS and CT. In region-based analysis, sensitivity of (18)F-DOPA PET was 95% (90-98) versus 66% (57-74) for SRS, 57% (48-66) for CT, and 79% (70-86) for combined SRS and CT (p=0.0001, PET vs combined SRS and CT). In individual-lesion analysis, corresponding sensitivities were 96% (95-98), 46% (43-50), 54% (51-58), and 65% (62-69; p<0.0001 for PET vs combined SRS and CT).

INTERPRETATION

If the improved tumour localisation seen with (18)F-DOPA-PET compared with conventional imaging is confirmed in future studies, this imaging method could replace use of SRS, help improve prediction of prognosis, and be used to assess patients' response to treatment for carcinoid tumours.

Cushing's Syndrome: important issues in diagnosis and management

CONTEXT

The diagnosis, differential diagnosis, and treatment of Cushing's syndrome are challenging problems in clinical endocrinology. We focus on critical questions addressing screening for Cushing's syndrome, differentiation of Cushing's subtypes, and treatment options.

EVIDENCE ACQUISITION

Ovid's MEDLINE (1996 through April 2006) was used to search the general literature. We also relied on previously published reviews and a recent monograph and cite a mix of primary articles and recent reviews.

EVIDENCE SYNTHESIS

Although this article represents our opinion, it draws heavily on a recent consensus statement from experts in the field and a recent monograph on Cushing's syndrome.

CONCLUSIONS

We concluded that: 1) measurement of late-night or bedtime salivary cortisol is a useful approach to screen for Cushing's syndrome; 2) measurement of suppressed plasma ACTH by immunometric assay is useful to differentiate ACTH-dependent and -independent Cushing's syndrome; 3) inferior petrosal sinus sampling for ACTH should be performed in patients with ACTH-dependent hypercortisolism in whom a pituitary magnetic resonance imaging is normal or equivocal (in the absence of a pituitary ACTH gradient, prolactin levels should be measured to confirm the integrity of venous sampling); 4) computed tomography of the chest and abdomen and somatostatin receptor scintigraphy should be performed in patients with the occult ectopic ACTH syndrome; and 5) patients with Cushing's disease should be referred to a neurosurgeon with extensive experience operating on corticotroph microadenomas. Bilateral laparoscopic adrenalectomy should be considered in patients with Cushing's disease who fail therapies directed at the pituitary.

Gastrointestinal carcinoids: the evolution of diagnostic strategies

Carcinoid tumors are rare, often insidious neoplasms arising from neuroendocrine cells. The majority arise in the gastrointestinal system, and are often incidentally found during investigation, although some may present as an emergency bleed or perforation. The prosaic symptoms of flushing, diarrhea, and sweating are often overlooked; thus, the diagnosis is usually much delayed and the tumor is advanced at presentation. This diagnostic delay renders effective management difficult and adversely affects outcome. This overview provides a current assessment of the evolution of the diagnostic techniques available to establish an accurate biochemical (5-hydroxyindole-3-acetic acid and chromogranin A) and topographic diagnosis (octreoscan, radio-labeled metaidobenzylguanidine, computerized tomography, magnetic resonance imaging, positron emission tomography, enteroclysis, endoscopic ultrasound, enteroscopy, capsule endoscopy, and angiography) of carcinoid tumors. The utility and shortcomings of the respective modalities available are evaluated. Although considerable advances have been made in establishing the diagnosis of carcinoid tumors and in defining the topography of metastatic disease, the major limitation is the inability to establish an early and timely diagnosis before the advent of metastatic disease.

Advances in alimentary tract imaging

Advances in imaging techniques are changing the way radiologists undertake imaging of the gastrointestinal tract and their ability to answer questions posed by surgeons. In this paper we discuss the technological improvements of imaging studies that have occurred in the last few years and how these help to better diagnosing alimentary tract disease.

Cushing's syndrome

Cushing's syndrome results from lengthy and inappropriate exposure to excessive glucocorticoids. Untreated, it has significant morbidity and mortality. The syndrome remains a challenge to diagnose and manage. Here, we review the current understanding of pathogenesis, clinical features, diagnostic, and differential diagnostic approaches. We provide diagnostic algorithms and recommendations for management.

The management of insulinoma

BACKGROUND

Insulinomas are rare tumours. Their clinical presentation, localization techniques and operative management were reviewed.

METHODS

An electronic search of the Medline, Embase and Cochrane databases was undertaken for articles published between January 1966 and June 2005 on the history, presentation, clinical evaluation, use of imaging techniques for tumour localization and operative management of insulinoma.

RESULTS AND CONCLUSION

Most insulinomas are intrapancreatic, benign and solitary. Biochemical diagnosis is obtained during a supervised 72-h fast. Non-invasive preoperative imaging techniques to localize lesions continue to evolve. Intraoperative ultrasonography can be combined with other preoperative imaging modalities to improve tumour detection. Surgical resection is the treatment of choice. In the absence of preoperative localization and intraoperative detection of an insulinoma, blind pancreatic resection is not recommended.

18Flurodeoxyglucose positron emission tomography in the localization of ectopic ACTH-secreting neuroendocrine tumours

OBJECTIVE

Neuroendocrine tumours (NET) are a rare cause of Cushing's syndrome. These tumours can be very small and therefore difficult to identify. Current localization techniques include CT, MRI and radioisotope scanning, but in a proportion of cases the NET remains occult. Positron emission tomography (PET) scanning, is a relatively new imaging modality that is increasingly used to detect and monitor lesions with high metabolic activity. We report on the use of PET scanning in the evaluation of the ectopic ACTH syndrome.

PATIENTS

Three patients with ectopic ACTH-dependent Cushing's syndrome with varying difficulty in NET localization are included in the report.

MEASUREMENT

Positron emission tomography scanning using 18flurodeoxyglucose (FDG) identifies tissue with high metabolic activity. 18FDG-PET scanning was used in each of these patients and the imaging is presented along with biochemical data.

RESULTS

In each case the NET was easily identified using 18FDG-PET, aiding clinical decision making and therapeutic outcome. A cure was identified by clinical resolution of symptoms and undetectable ACTH levels postsurgery.

CONCLUSIONS

18FDG-PET assisted in localizing small metabolically active NETs, suggesting this imaging modality may have a useful role in identifying NET causing Cushing's syndrome as a result of ectopic ACTH production.

Carcinoid syndrome: diagnosis and medical management

Gastro-intestinal carcinoids are slow growing tumors arising from enterochromaffin or Kulchitsky cells. Their clinical presentation depends on what combination of bioactive substances is secreted. Midgut carcinoid can present with the carcinoid syndrome in the presence of liver metastases. Its most typical clinical manifestations include cutaneous flushing and diarrhea. A nonspecific biochemical tumor marker for carcinoid tumors is serum chromogranin A and a specific marker for the carcinoid syndrome is the increased urinary excretion of 5-hydroxy indole acetic acid (5-HIAA). Localizing studies in carcinoid tumors/syndrome are: transabdominal ultrasonography (US), endoscopy, endoscopic US, videocapsule endoscopy, computerized tomography, magnetic resonance imaging, selective abdominal angiography, 111In-pentetreotide scintigraphy (and intraoperative radionuclide probe), 123I (131I)-metaiodobenzylguanidine (MIBG) scintigraphy, bone scintigraphy and 11C-5-HT positron emission tomography (PET). Therapies for carcinoid tumors/syndrome are: surgery, somatostatin analogs, interferon-alpha, radiotherapy, liver dearterialization, liver (chemo, or radio)-embolization, alcohol sclerotherapy of liver metastases, radiofrequency ablation of liver metastases, cryosurgery of liver metastases, occasionally liver transplantation, radiotherapy-coupled somatostatin analogs, 131I-MIBG and occasionally chemotherapy.

Functional imaging of neuroendocrine tumours with PET

Several pathophysiological attributes of neuroendocrine tumours (NET) can be addressed by specific radiolabelled probes. This paper provides an overview on the different radiopharmaceuticals that have been developed for Positron Emission Tomography (PET) of neuroendocrine tumours. A review of the literature on 18F-fluordeoxyglucose (FDG), biogenic amine precursors, somatostatin analogues and hormone syntheses markers is presented. Due to the highly specific tracers that lack any clear anatomical landmarking the advantages of integrated PET/CT are obvious. Amine precursors should be employed in most gastroenteropancreatic NET, FDG should be preserved for more aggressive, less differentiated NETs. Somatostatin analogues are the most promising tracers, since they can improve dosimetry in cases in which radiopeptide therapies are planned. In conclusion, the individual diagnostic approach using PET or the integrated PET/CT should be tailored depending on the histological classification and the differentiation of the tumour.

Carbidopa pretreatment improves image interpretation and visualisation of carcinoid tumours with 11C-5-hydroxytryptophan positron emission tomography

PURPOSE

Positron emission tomography (PET) with 11C-5-hydroxytryptophan (5-HTP) as tracer is a promising imaging instrument in the management of patients with neuroendocrine tumours (NETs). However, high radioactivity concentrations in the urinary collecting system sometimes produce image reconstruction artefacts that can make detection of small NETs difficult. As a means to decrease urinary excretion of radioactivity and thereby improve image quality, we examined the effect of pretreatment with carbidopa (CD), a peripheral inhibitor of aromatic amino acid decarboxylase (AADC), which converts 5-HTP to serotonin (5-hydroxytryptamine, 5-HT).

METHODS

Six patients with midgut carcinoid metastases were examined with 11C-5-HTP PET before and 1 h after oral administration of 100 or 200 mg of CD.

RESULTS

There was a fourfold significant reduction of tracer uptake in the urinary collecting system after CD administration (p=0.0277, n=6), with a mean standard uptake value (SUV) of 155+/-195 before CD and 39+/-14 after CD. In tumour lesions there was a significant increase in SUV after CD administration (p<0. 0001, n=18), with a mean SUV of 11+/-3 before CD and 14+/-3 after CD. There was no difference between the doses (100 and 200 mg) of CD in this respect. In all patients, image interpretation and tumour detection were markedly improved after CD administration.

CONCLUSION

We conclude that CD premedication improves 11C-5-HTP PET image quality and facilitates detection of NET lesions. Because of the similarity of metabolic pathways, this method could probably be applied to improve PET imaging using other tracers like 18F-DOPA and 11C-DOPA.

Octreotide exerts only acute, but no sustained, effects on MRI enhancement of liver metastases in carcinoid syndrome

We have investigated the acute and sustained hemodynamic effects of octreotide on hepatic metastases of midgut carcinoids using contrast-enhanced dynamic magnetic resonance imaging (MRI). Seven patients with the carcinoid syndrome and metastasized midgut carcinoid tumors underwent functional dynamic multi-phase gadolinium-enhanced MRI of selected liver metastases at baseline and 60 min after the subcutaneous (s.c.) administration of 100 microg octreotide, and also after 3 months with three times daily (t.i.d.) 100 microg octreotide s.c. Baseline MRIs showed the typical aspect of carcinoid liver metastases with a very bright signal on the T2-weighted sequences and intense enhancement in the arterial phase after injection of gadolinium-diethylenetriaminepentaacetate. MRIs 60 min after the s.c. administration of 100 microg octreotide showed a 34.9 +/- 6.2% (mean +/- SD) reduction in relative enhancement in the selected liver metastases as compared to baseline. In 2 patients, however, there was no (significant) reduction in the relative enhancement in the selected liver metastases 60 min after the s.c. administration of 100 microg octreotide as compared to baseline. Only in 2 patients did the MRIs at 3 months show a decrease in relative enhancement in one of the selected liver metastases. At 3 months, with 100 microg octreotide s.c. t.i.d., there was no correlation between the change in relative enhancement on MRI and the change in 24-hour 5-HIAA excretion. There is thus only an acute effect of octreotide on the perfusion of liver metastases. This study further shows that contrast-enhanced dynamic MRI can be a very useful tool for studying hemodynamic effects of medical therapies on liver metastases in patients with metastatic midgut carcinoids.