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

Comparison of diagnostic efficacy of 18F-FDG PET/CT and 68Ga-DOTANOC PET/CT in ectopic adrenocorticotropic hormone syndrome

PURPOSE

Fluorine-18 (¹⁸F)-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and gallium-68 (⁶⁸Ga)-somatostatin analog (SSA) PET/CT imaging have been increasingly used in ectopic adrenocorticotropic hormone syndrome (EAS); however, the diagnostic efficacies of these two methods in patients with EAS remain unclear. Our study aimed to compare the diagnostic efficacies of ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTANOC PET/CT in EAS.

METHODS

The clinical and imaging data of 68 patients with EAS who underwent ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTANOC PET/CT examinations from December 2016 to April 2021 were analyzed retrospectively, and the diagnostic efficacies of these methods were compared.

RESULTS

In 37 cases, imaging was performed to locate the primary tumor lesion (localization group), and in 31 to evaluate tumor load or metastasis (staging group). Primary tumors were detected in 48.65% (18/37) of the localization group patients. According to scan-based analysis, the tumor lesion detection rates and false positive rates of ¹⁸F-FDG PET/CT imaging and ⁶⁸Ga-DOTANOC PET/CT imaging were 18.92% vs. 45.95% (p < 0.05) and 21.62% vs. 2.70% (p < 0.05) respectively. For lesion-based analysis, the tumor lesion detection rates and false positive rates were 24.13% vs. 58.62% (p >0.05) and 31.04% vs. 3.45% (p < 0.05). In 90.32% (28/31) of the staging group patients, 286 of 292 lesions were confirmed as tumor lesions. Based on scan analysis, the detection rates and false positive rates of ¹⁸F-FDG PET/CT imaging and ⁶⁸Ga-DOTANOC PET/CT imaging were 83.87% vs. 67.74% (p > 0.05) and 12.90% vs. 9.68% (p > 0.05) respectively. Based on lesion analysis, the detection rate and false positive rates were 93.84% vs. 54.80% (p < 0.05) and 1.37% vs. 1.03%(p > 0.05).

CONCLUSION

⁶⁸Ga-DOTANOC PET/CT imaging may be more suitable than ¹⁸F-FDG PET/CT for identifying the primary tumor in patients with EAS, while ¹⁸F-FDG PET/CT may be more advantageous than ⁶⁸Ga-DOTANOC PET/CT for patients with suspected metastasis.

Head-to-head comparison of 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT in localizing tumors with ectopic adrenocorticotropic hormone secretion: a prospective study

PURPOSE

Localizing the source of ectopic adrenocorticotropic hormone secretion (EAS) is challenging. This study compared the diagnostic value of 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT in tumors with EAS.

METHODS

Thirty-six patients with a suspicion of EAS were enrolled to undergo both 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT within 4 weeks for comparison. Twenty-three underwent surgical resection or biopsy. Immunohistochemical staining for SSTR2 and Ki-67 was performed to correlate with 68Ga-DOTATATE uptake and 18F-FDG uptake, respectively.

RESULTS

EAS tumors were observed in 20/23 patients. Among the 20 patients with histologically proven EAS tumors, 68Ga-DOTATATE PET/CT correctly identified the tumor in 15 (75.0%), with an SUVmax ranging from 1.4 to 20.7 (6.7 ± 5.5). 18F-FDG PET/CT correctly identified the tumor in 12 (60.0%) patients, with an SUVmax ranging from 1.8 to 10.0 (4.0 ± 2.1). Moreover, 68Ga-DOTATATE PET/CT unmasked the sources of EAS in 6 patients with negative 18F-FDG uptake, and 18F-FDG PET/CT unmasked the sources in 3 patients with negative 68Ga-DOTATATE uptake, resulting in EAS tumors being identified in 18 (90%) patients by combining 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT.

CONCLUSIONS

68Ga-DOTATATE PET/CT and 18F-FDG PET/CT are complementary in localizing and discriminating the source of EAS. 68Ga-DOTATATE PET/CT combined with 18F-FDG PET/CT had higher detection rate than each alone.

TRIAL REGISTRATION

68Ga-DOTATATE PET/CT in Neuroendocrine Tumors (NCT04041882) URL OF REGISTRY: https://clinicaltrials.gov/ct2/show/NCT04041882.

Ectopic ACTH syndrome of different origin-Diagnostic approach and clinical outcome. Experience of one Clinical Centre

PURPOSE

Ectopic Cushing Syndrome (EAS) is a rare condition responsible for about 5-20% of all Cushing syndrome cases. It increases the mortality of affected patients thus finding and removal of the ACTH-producing source allows for curing or reduction of symptoms and serum cortisol levels. The aim of this study is to present a 20-year experience in the diagnosis and clinical course of patients with EAS in a single Clinical Centre in Southern Poland as well as a comparison of clinical course and outcomes depending on the source of ectopic ACTH production-especially neuroendocrine tumors with other neoplasms.

METHODS

Twenty-four patients were involved in the clinical study with EAS diagnosed at the Department of Endocrinology between years 2000 and 2018. The diagnosis of EAS was based on the clinical presentation, hypercortisolemia with high ACTH levels, high dose dexamethasone suppression test and/or corticotropin-releasing hormone tests. To find the source of ACTH various imaging studies were performed.

RESULTS

Half of the patients were diagnosed with neuroendocrine tumors, whereby muscle weakness was the leading symptom. Typical cushingoid appearance was seen in merely a few patients, and weight loss was more common than weight gain. Patients with neuroendocrine tumors had significantly higher midnight cortisol levels than the rest of the group. Among patients with infections, we observed a significantly higher concentrations of cortisol 2400 levels in gastroenteropancreatic neuroendocrine tumors. Chromogranin A correlated significantly with potassium in patients with neuroendocrine tumors and there was a significant correlation between ACTH level and severity of hypokalemia.

CONCLUSION

EAS is not common, but if it occurs it increases the mortality of patients; therefore, it should be taken into consideration in the case of coexistence of severe hypokalemia with hypertension and muscle weakness, especially when weight loss occurs. Because the diagnosis of gastroenteropancreatic neuroendocrine tumor worsens the prognosis-special attention should be paid to these patients.

Functional imaging in ectopic Cushing syndrome

PURPOSE OF REVIEW

Ectopic adrenocorticotropic hormone (ACTH)-secreting tumors are commonly small, yet they often lead to fulminant forms of Cushing syndrome. High-resolution functional imaging modalities, such as [Ga]-DOTATATE, have been recently introduced in clinical practice for the identification of neuroendocrine tumors. In this review, we focus on the performance of [Ga]-DOTATATE as a tool for localizing primary and metastatic sources of ectopic Cushing syndrome (ECS).

RECENT FINDINGS

Prompt surgical removal of ectopic ACTH-secreting tumors is the mainstay of therapy in patients with ECS. Detecting such tumors with conventional cross-sectional imaging is often unsuccessful, owing to their small size. [Ga]-DOTATATE has been approved in 2016 by the Federal Drug Administration for imaging well differentiated neuroendocrine tumors. Data regarding the performance of [Ga]-DOTATATE for detecting ectopic ACTH-secreting tumors remain limited, in part owing to the recent introduction of this imaging modality in clinical practice, and in part because of the low prevalence of ECS. Nevertheless, [Ga]-DOTATATE has been reported to be useful in identifying primary and metastatic ectopic ACTH-secreting lesions that were not apparent on other imaging studies, impacting the clinical care of many patients with ECS.

SUMMARY

[Ga]-DOTATATE-based imaging, which targets the somatostatin receptors abundantly expressed in neuroendocrine tumors, has generally high, although variable resolution in detecting the source(s) of ECS.

PET imaging in ectopic Cushing syndrome: a systematic review

Cushing syndrome due to endogenous hypercortisolism may cause significant morbidity and mortality. The source of excess cortisol may be adrenal, pituitary, or ectopic. Ectopic Cushing syndrome is sometimes difficult to localize on conventional imaging like CT and MRI. After performing a multilevel thoracoabdominal imaging with CT, the evidence regarding the use of radiotracers for PET imaging is unclear due to significant molecular and etiological heterogeneity of potential causes of ectopic Cushing's syndrome. In our systematic review of literature, it appears that GalLium-based (Ga68) somatostatin receptor analogs have better sensitivity in diagnosis of bronchial carcinoids causing Cushing syndrome and FDG PET appears superior for small-cell lung cancers and other aggressive tumors. Further large-scale studies are needed to identify the best PET tracer for this condition.

A role for 11C-methionine PET imaging in ACTH-dependent Cushing's syndrome

OBJECTIVE

We report our experience of functional imaging with (11)C-methionine positron emission tomography-computed tomography (PET-CT) co-registered with 3D gradient echo (spoiled gradient recalled (SPGR)) magnetic resonance imaging (MRI) in the investigation of ACTH-dependent Cushing's syndrome.

DESIGN

Twenty patients with i) de novo Cushing's disease (CD, n=10), ii) residual or recurrent hypercortisolism following first pituitary surgery (±radiotherapy; n=8) or iii) ectopic Cushing's syndrome (n=2) were referred to our centre for functional imaging studies between 2010 and 2015. Six of the patients with de novo CD and five of those with persistent/relapsed disease had a suspected abnormality on conventional MRI.

METHODS

All patients underwent (11)C-methionine PET-CT. For pituitary imaging, co-registration of PET-CT images with contemporaneous SPGR MRI (1 mm slice thickness) was performed, followed by detailed mapping of (11)C-methionine uptake across the sella in three planes (coronal, sagittal and axial). This allowed us to determine whether suspected adenomas seen on structural imaging exhibited focal tracer uptake on functional imaging.

RESULTS

In seven of ten patients with de novo CD, asymmetric (11)C-methionine uptake was observed within the sella, which co-localized with the suspected site of a corticotroph microadenoma visualised on SPGR MRI (and which was subsequently confirmed histologically following successful transsphenoidal surgery (TSS)). Focal (11)C-methionine uptake that correlated with a suspected abnormality on pituitary MRI was seen in five of eight patients with residual or recurrent Cushing's syndrome following first TSS (and pituitary radiotherapy in two cases). Two patients elected to undergo repeat TSS with histology confirming a corticotroph tumour in each case. In two patients with the ectopic ACTH syndrome, (11)C-methionine was concentrated in sites of distant metastases, with minimal uptake in the sellar region.

CONCLUSIONS

(11)C-methionine PET-CT can aid the detection of ACTH-secreting tumours in Cushing's syndrome and facilitate targeted therapy.

Conventional and Nuclear Medicine Imaging in Ectopic Cushing's Syndrome: A Systematic Review

CONTEXT

Ectopic Cushing's Syndrome (ECS) can be a diagnostic challenge with the hormonal source difficult to find. This study analyzes the accuracy of imaging studies in ECS localization.

EVIDENCE ACQUISITION

Systematic review of medical literature for ECS case series providing individual patient data on at least one conventional imaging technique (computed tomography [CT]/magnetic resonance imaging) and one of the following: 111In-pentetreotide (OCT), 131I/123I-metaiodobenzylguanidine, 18Ffluoro-2-deoxyglucose-positron emission tomography (FDG-PET), 18F-fluorodopa-PET (F-DOPA-PET), 68Ga- DOTATATE-PET/CT or 68Ga-DOTATOC-PET/CT scan (68Gallium-SSTR-PET/CT).

EVIDENCE SUMMARY

The analysis comprised 231 patients (females, 50.2%; age, 42.617 y). Overall, 52.4%(121/231) had "overt" ECS,18.6% had "occult" ECS, and 29% had "covert" ECS. Tumors were located in the lung (55.3%), mediastinum-thymus (7.9%), pancreas (8.5%), adrenal glands (6.4%), gastrointestinal tract (5.4%), thyroid (3.7%), and other sites (12.8%), and primary tumors were mostly bronchial neuroendocrine tumors (NETs) (54.8%), pancreatic NETs (8%), mediastinum-thymus NETs (6.9%), gastrointestinal NETs (5.3%), pheochromocytoma (6.4%), neuroblastoma (3.2%), and medullary thyroid carcinoma (3.2%). Tumors were localized byCTin66.2%(137/207), magnetic resonance imaging in 51.5% (53/103), OCT in 48.9% (84/172), FDG-PET in 51.7% (46/89), F-DOPAPET in 57.1% (12/21), 131/123I-metaiodobenzylguanidine in 30.8% (4/13), and 68Gallium-SSTRPET/CT in 81.8% (18/22) of cases. Molecular imaging discovered 79.1% (53/67) of tumors unidentified by conventional radiology, with OCT the most commonly used, revealing the tumor in 64%, followed by FDG-PET in 59.4%. F-DOPA-PET was used in only seven covert cases (sensitivity, 85.7%). Notably, 68Gallium-SSTR-PET/CT had 100% sensitivity among covert cases.

CONCLUSIONS

Nuclear medicine improves the sensitivity of conventional radiology when tumor site identification is problematic. OCT offers a good availability/reliability ratio, and FDG-PET was proven useful. 68Gallium-SSTR-PET/CT use was infrequent, despite offering the highest sensitivity.

The value of somatostatin receptor imaging with In-111 Octreotide and/or Ga-68 DOTATATE in localizing Ectopic ACTH producing tumors

OBJECTIVE

We aimed to evaluate the value of somatostatin receptor imaging (SRI) with In-111 octreotide and Ga-68 DOTATATE in localizing ectopic ACTH producing tumors.

METHODS

Nineteen patients who had In-111 octreotide somatostatin receptor scintigraphy (SRS) and/or Ga-68 DOTATATE PET-CT to localize ectopic ACTH producing tumors between the years 2000 and 2012 were included retrospectively in our study. The results of SRI were compared with clinical onset, radiological findings and surgical data of the patients.

RESULTS

Sixteen In-111 octreotide SRS and five Ga-68 DOTATATE PET-CT were performed in 19 patients. In eight out of 19 patients, ectopic ACTH secretion site could be detected. In five patients, SRS showed pathologic uptake. In four of these patients, surgery revealed pulmonary carcinoid tumors and in one patient pancreatic neuroendocrine tumor. In one patient, Ga-68 DOTATATE PET-CT revealed pathologic uptake in lung nodule which came out to be pulmonary carcinoid tumor. In another patient who had resection of metastases of atypical carcinoid tumor prior to scans, new metastatic foci were detected both with SRS and Ga-68 DOTATATE PET-CT imaging. In one patient, although SRS was negative, CT which was performed three years later showed a lung nodule diagnosed as pulmonary carcinoid tumor. In 11 patients, ectopic ACTH secretion site could not be detected. In 10 of those patients, scintigraphic and radiological imaging did not show any lesions and in one patient, Ga-68 DOTATATE PET-CT was false positive.

CONCLUSION

SRI has a complementary role with radiological imaging in localizing ectopic ACTH secretion sites. PET-CT imaging with Ga-68 peptide conjugates is a promising new modality for this indication.

CONFLICT OF INTEREST

None declared.

Nuclear medicine imaging in the evaluation of endocrine hypertension

Endocrine hypertension forms a small (< 5%) but curable subset of patients with hypertension. Common endocrine causes of hypertension include pheochromocytoma, Cushing's syndrome, primary hyperaldosteronism, and thyroid disorders. Nuclear medicine imaging plays an important role in evaluation of patients with endocrine hypertension. It has established role in patients of pheochromocytoma/paraganglioma, Cushing's syndrome, aldosteronism, and thyroid disorders. We present a brief overview of role of nuclear medicine imaging in endocrine hypertension. Development of newer radiotracers might further broaden the role of nuclear medicine in these patients.

Altered FDG uptake patterns in pediatric lymphoblastic lymphoma patients receiving induction chemotherapy that includes very high dose corticosteroids

BACKGROUND

Altered FDG uptake patterns were noted in certain lymphoblastic lymphoma patients during therapy.

OBJECTIVE

To describe these altered FDG uptake patterns and their relationship to chemotherapy.

MATERIALS AND METHODS

Thirty-five FDG PET or PET/CT scans obtained in 11 children with lymphoblastic lymphoma were retrospectively reviewed. FDG uptake patterns were recorded. SUV measurements were performed in liver and facial soft tissues. Results were correlated with induction chemotherapy regimens.

RESULTS

Six of the children had transiently altered FDG uptake with increased uptake in the superficial soft tissues, most notably involving the face. Altered uptake was noted approximately 1 month after initiation of chemotherapy and subsequently resolved. Hepatic uptake was transiently reduced on the 1-month scan in all six children with increased facial uptake. No significant FDG uptake in lymphoma was seen on five of six scans with altered uptake; however, two of these five affected children had FDG uptake in lymphoma on the next follow-up examination. Blood glucose levels in the affected children were in the normal range. All six children with altered FDG uptake received the same induction chemotherapy regimen, which included very high doses of corticosteroids.

CONCLUSIONS

Children with lymphoblastic lymphoma on induction chemotherapy protocols including very high doses of corticosteroids transiently demonstrated altered FDG uptake patterns, including increased superficial facial uptake and reduced hepatic uptake. The facial uptake is probably the FDG PET equivalent of Cushingoid facies. Caution in interpreting scans with this altered FDG uptake pattern is suggested, as uptake at sites of lymphomatous involvement may potentially be affected.

Cushing syndrome secondary to ectopic adrenocorticotropic hormone secretion: the University of Texas MD Anderson Cancer Center Experience

BACKGROUND

Cushing syndrome (CS) secondary to ectopic adrenocorticotropic hormone (ACTH) secretion (EAS) has been described in association with a variety of tumors. The current experience with this syndrome was based on a few case series and individual case reports. Limited data were available about the tumors associated with CS-EAS in a cancer center setting. In this report, the authors have described their experience with CS-EAS at The University of Texas MD Anderson Cancer Center to further enhance the current understanding and management of this syndrome.

METHODS

This was a retrospective review of 43 patients with CS-EAS who were diagnosed between 1979 and 2009 at The University of Texas MD Anderson Cancer Center.

RESULTS

Different neuroendocrine tumors were associated with CS-EAS. Twenty-one patients (48.9%) had tumors located in the chest cavity, with bronchial carcinoid and small cell lung cancer representing the 2 most common causes. The ACTH source remained occult in 4 patients (9.3%) despite extensive workup. Clinical presentation varied, and the classic features of CS were not evident in some patients. Death occurred in 27 patients (62.8%), and the median overall survival was 32.2 months. Major morbidities included new-onset or worsening hyperglycemia (77%), symptomatic venous thromboembolism (14%), and infections (23%).

CONCLUSIONS

In patients with CS-EAS who attended a comprehensive cancer center, tumors originating in the chest cavity were the leading tumors associated with this syndrome. The authors suspect that CS-EAS is under reported because of the atypical presentation in some patients. Thus, they suggest careful evaluation of patients with neuroendocrine tumors to avoid missing coexisting CS-EAS.

The ectopic ACTH syndrome

Ectopic Cushing's syndrome usually relates to the ectopic ACTH syndrome (EAS) and represents ∼20% of ACTH-dependent and ∼10% of all types of Cushing's syndrome (CS). Nearly any neuroendocrine or non-endocrine tumours may be associated with EAS, but the more prevalent tumours are bronchial carcinoids, small cell lung carcinomas, pancreatic carcinoids, thymic carcinoids, medullary carcinomas of the thyroid, and phaeochromocytomas. Occult tumours are highly represented in all the series (12-38%) and constitute the more challenging cases of EAS, requiring long term follow-up. The lack of any completely reliable diagnostic test procedure and imaging to clearly reveal the source of EAS suggests that we should adopt a step-by-step multidisciplinary approach for their diagnosis and therapeutic management. Clinical features are often similar in ACTH-dependent CS, but the rapid onset and progress may suggest an ectopic source. A combination of biochemical tests and imaging studies seems the most appropriate approach for the prompt identification of EAS, even if there are several pitfalls to be avoided along the way. The most appropriate management for cure of EAS, when its source is identified, is surgical excision after controlling the hypercortisolaemia by inhibitors of cortisol secretion and other newer modalities alone or in combination; bilateral adrenalectomy remains an alternative option. Tumour histology, the presence of metastases and the effective control of hypercortisolaemia affect mortality and morbidity. If a source repeatedly fails to be found, the prognosis is often favourable but the identification of a malignant tumour should still be sought during life-long follow-up to avoid the calamity of misdiagnosis.

Utility of various functional and anatomic imaging modalities for detection of ectopic adrenocorticotropin-secreting tumors

CONTEXT

Because ectopic ACTH-secreting (EAS) tumors are often occult, improved imaging is needed.

OBJECTIVE

Our objective was to evaluate the utility of [(111)In-DTPA-d-Phe]pentetreotide scintigraphy [octreotide (OCT)] imaging at 6 mCi [low OCT (LOCT)] and 18 mCi [high OCT (HOCT)], [(18)F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) and [(18)F]l-3,4-dihydroxyphenylalanine (F-DOPA)-PET scans, computed tomography (CT), and magnetic resonance imaging (MRI).

DESIGN AND SETTING

The study was a prospective evaluation at a clinical research center.

PATIENTS

Forty-one subjects participated, 30 (17 female) with resected EAS tumors and 11 (three female) with occult EAS, based on inferior petrosal sinus sampling results and imaging studies.

INTERVENTION

INTERVENTION included CT and MRI of neck, chest, abdomen, LOCT (with or without HOCT) and FDG- or F-DOPA-PET without CT every 6-12 months.

MAIN OUTCOME MEASURE

Tumor identification was the main outcome measure.

RESULTS

Most recent results were analyzed. Eighteen patients had tumor resected on the first visit; otherwise, surgery occurred 33 +/- 25 (9-99) months later. Tumor size was 1.9 +/- 1.7 (0.8-8.0) cm; 83% were intrathoracic. CT, MRI, LOCT, HOCT, FDG-PET, and F-DOPA-PET had sensitivities per patient of 93% [95% confidence interval (CI) = 79-98%], 90% (95% CI = 74-96%), 57% (95% CI = 39-73%), 50% (95% CI = 25-75%), 64% (95% CI = 35-85%), and 55% (95% CI = 28-79%) and positive predictive values (PPV) per lesion of 66, 74, 79, 89, 53, and 100%, respectively. LOCT and PET detected only lesions seen by CT/MRI; abnormal LOCT or F-DOPA-PET improved PPV of CT/MRI. By modality, the fraction of patients with one or more false-positive findings was 50% by CT, 31% by MRI, 18% by L/HOCT, and 18% by FDG-PET. Eight occult EAS patients had 64 +/- 58 (9-198) months follow-up; others had none.

CONCLUSIONS

High sensitivity and PPV suggest thoracic CT/MRI plus LOCT scans for initial imaging, with lesion confirmation by two modalities.

The role of integrated (18)F-FDG PET/CT in identification of ectopic ACTH secretion tumors

The role of (18)F-Flurodeoxyglucose positron emission tomography ((18)F-FDG PET) scan in localization of ectopic Cushing's syndrome (EAS) tumor is still controversial. Here, we report on the use of integrated (18)F-FDG PET and computed tomography ((18)F-FDG PET/CT) in localization of EAS tumors in patients with ectopic Cushing's syndrome. Five patients, three men and two women, were reported, whose endocrine investigations and negative pituitary imaging were suggestive of ectopic ACTH secretion. (18)F-FDG PET/CT was performed to identify the source of ACTH secretion. Then the patients were suggested to perform pathologic examination. It turned out that all of these five patients have abnormal markedly intense FDG uptake lesions on (18)F-FDG PET/CT images. Four of them underwent lesion resection, whose plasma ACTH and serum cortisol levels returned to normal after the surgery. Also, they were at last remission from all the symptoms. Pathologic results showed one thymic carcinoid, one pulmonary carcinoid, one thymoma, and one pulmonary carcinoid with upper mediastinum carcinoid. Unfortunately, one patient died due to severe infection and electrolyte disorders. (18)F-FDG PET/CT technology integrates PET and CT imaging in one device so as to increase the accuracy of tumor localization and further improve the prognosis of the patients by curative resection.

Utility of [(18)F] fluoro-2-deoxy-D: -glucose positron emission tomography in the localization of ectopic ACTH-secreting tumors

Ectopically ACTH producing tumors may be difficult to localize by conventional radiology and functional imaging may be helpful. Case 1: 31-year-old man was diagnosed with ectopic ACTH-dependent Cushing's syndrome (ECS). Thorax CT revealed a 1.3 cm nodular opacity in upper left lobe, suggestive of residual lesion. [(18)F] fluoro-2-deoxy-D: -glucose ([(18)F] FDG) positron emission tomography ([(18)F] FDG PET) scan revealed mild glycolytic metabolic activity. Pathological examination confirmed an ACTH-positive carcinoid tumor. Case 2: 53-year-old woman presented with very rapid onset ECS. Pituitary MRI was normal. Thorax CT revealed no tumoral lesion. Abdominal and pelvic MRI showed images suggestive of hepatic and iliac, femoral and lumbar secondary implants. [(18)F] FDG PET scan revealed intense uptake in uterus, especially cervix, suggesting this to be the primary tumor site. These cases illustrate the role of [(18)F] FDG PET in the investigation of an ECS where conventional imaging studies were not elucidative in the search for a responsible tumor.

The diagnostic value of fused positron emission tomography/computed tomography in the localization of adrenocorticotropin-secreting pituitary adenoma in Cushing's disease

Despite the high resolution of magnetic resonance imaging (MRI) of the pituitary gland, up to 40% of cases of Cushing's disease (CD) have normal MRI. Fused images of positron emission tomography and computed tomography (PET-CT) may have a potential diagnostic role in CD in general and in such cases in particular. Objective of this study is to explore the diagnostic potential of PET-CT for localization of adrenocorticotropin-secreting pituitary adenomas in CD. PET-CT was performed in 12 cases with de novo (7 cases) or persistent CD (5 cases) that were proven to have CD on biochemical, radiological and/or histopathological findings. These cases had a definite CD confirmed on histopathological and immunostaining examination of the subsequent transphenoidal surgical specimens (10 cases) and/or bilateral inferior petrosal sinus sampling (IPSS, 4 cases). PET-CT was positive in 7 of the 12 cases of CD (58%) showing a focal area of uptake in the pituitary gland. In these seven cases, MRI was positive in six (85.7%) but negative in one case (14.3%). In the other five cases with negative PET-CT, MRI was positive in two and negative in three cases. Of four cases with negative MRI, PET-CT was positive in one case (25%). We conclude that PET-CT is positive in around 60% of the cases of CD. Although the majority of cases with positive PET-CT had positive MRI, PET-CT may detect some cases with negative MRI and thus provides important diagnostic information. If these findings are confirmed in larger studies, PET-CT might become an important diagnostic technique, especially when the more invasive and technically demanding procedure of IPSS is not available or inconclusive.