Scintigraphic localization of phaeochromocytomas

123I-metaiodobenzylguanidine (MIBG) scintigraphy for the detection of adrenal and extra-adrenal phaeochromocytomas: CT and MRI correlation

CONTEXT

Evidence regarding the accuracy of [(123)I] metaiodobenzylguanidine (MIBG) imaging for phaeochromocytoma localization is currently limited to small series.

OBJECTIVE

We present the largest series of primary phaeochromocytomas in which the performance of [(123)I]MIBG has been evaluated and correlated with cross-sectional imaging.

DESIGN

We identified 76 patients with both preoperative [(123)I]MIBG and cross-sectional imaging for confirmed primary phaeochromocytoma between 1995 and 2005 at our institution. This comprised 60 adrenal tumours in 55 patients and 33 extra-adrenal tumours in 23 patients (2 patients had both adrenal and extra-adrenal tumours). Phaeochromocytoma metastases were not evaluated.

MAIN OUTCOME MEASURE(S)

[(123)I]MIBG studies were independently reviewed and correlated with CT and MRI examinations, as well as tumour functional status, to identify features that may predict a false negative [(123)I]MIBG result.

RESULTS

The overall sensitivity of [(123)I]MIBG was 75%. Tumour detection was lower for extra-adrenal (58%) vs. adrenal (85%) phaeochromocytomas (P = 0.005). For extra-adrenal tumours, [(123)I]MIBG demonstrated 8 of 14 carotid body, 2 of 2 intrathoracic, 8 of 14 retroperitoneal and 2 of 3 pelvic phaeochromocytomas. Overall, MRI and CT demonstrated 68 of 68 and 72 of 74 primary phaeochromocytomas, respectively. Tumour size correlated with [(123)I]MIBG uptake for adrenal (P = 0.009) but not extra-adrenal tumours. When tumours were adjusted for size, no other imaging feature or functional status correlated with [(123)I]MIBG negativity, although two large [(123)I]MIBG negative adrenal tumours contained large areas of necrosis or haemorrhage.

CONCLUSIONS

Extra-adrenal and small adrenal phaeochromocytomas are more likely to result in false negatives on [(123)I]MIBG. Tumoural necrosis or haemorrhage do not consistently relate to [(123)I]MIBG uptake, although adrenal phaeochromocytomas containing minimal solid tissue due to extensive necrosis may predict a negative [(123)I]MIBG result.

Nuclear medicine imaging of neuroendocrine tumours

Different tracers have been proposed in nuclear medicine to visualize neuroendocrine tumours: the majority are based on specific uptake mechanisms while some are aspecific. Among the most important gamma-emitting tracers, radiolabelled metaiodobenzylguanidine (123I or 121I-MIBG) and 111In-pentetreotide should be mentioned. In particular. good results can be obtained with 111In-pentetreotide scanning, which visualizes more than 70% of all neuroendocrine tumours and in some indications, as in gastro-entero-pancreatic (GEP) tumours, has a diagnostic sensitivity superior to that of conventional radiological imaging. Radiolabelled monoclonal antibodies have at present only a storical value, while a series of new peptides represent interesting subjects in areas currently being regarded. Positron emission tomography (PET) is a successful modality to detect cancer and recent years, has demonstrated a great diagnostic value in a large series of tumour types. 18F-deoxyglucose (FDG)-PET has also been used to diagnose tumours of neuroendocrine origin. Even if 18F-FDG has been successfully and widely employed in oncology, it has not demostrated a significant uptake in well differentiated neuroendocrine tissues. On the contrary, other positron emitter tracers seem to be more promising. A serotonin precursor 5-hydroxytryptophan (5-HTP) labelled with 11C has shown an increased uptake in carcinoids. This uptake seems to be selective and some clinical evidence has demonstrated that it allows the detection of more lesions with PET than with CT or octreotide scintigraphy. Another radiopharmaceutical in development for PET is 11C L-DOPA, which seems to be useful in visualizing endocrine pancreatic tumours. This Review summarizes the potential of several nuclear medicine techniques in the diagnosis of neuroendocrine tumours and stresses the renewed role of nuclear -medicine in the management of this disease.

Multiple venous sampling for catecholamine assay in the diagnosis of malignant pheochromocytoma

Malignant pheochromocytoma is a rare cause of hypertension and still has a high mortality rate. The most accurate way to localize a malignant pheochromocytoma is by a combination of scans, both CT and scintigraphy. Selective sampling of venous blood from multiple sites for plasma catecholamine levels is a safe and reliable technique and may be used successfully in some patients. A case is presented where venous sampling proved to be useful in preoperatively localizing a malignant pheochromocytoma and its metastatic lesions which both CT and ultrasound had failed to demonstrate.

Intraoperative localization of malignant pheochromocytoma by 123-I-metaiodobenzylguanidine single probe measurement

Metaiodobenzylguanidine (MIBG) imaging is a well-established method for locating intra- and extraadrenal pheochromocytomas. We investigated whether preoperative injection of 123-I-MIBG might be useful for intraoperative staging of chromaffine tumor cells. This was performed in a 46-year-old patient in whom the diagnosis of a malignant pheochromocytoma had been established by 123-I-MIBG imaging and enhanced catecholamine secretion. The rationale for intraoperative staging in this patient was a discrepancy between computed tomography (CI) of the abdomen and the radionuclide imaging, because scintigraphy revealed a mass with MIBG uptake in the right lower abdomen that could not be visualized by CT. We thus applied a preoperative dose of 4 mCi 123-I-MIBG and determined tissue activity by direct organ measurement. A right abdominal mass was thus identified with an activity of 10 x 10(4) impulses/s as compared to normal tissue (15 x 10(2)). The left-sided tumor was found to be identified correctly by prior CT and MIBG imaging. We thus conclude that intraoperative application of this single probe measurement might help to identify chromaffine tumor cells that have not been located fully by CT.

Clonidine-induced suppression of plasma catecholamines in states of adrenal medulla hyperfunction

To assess adrenal medulla activity in states of hyperfunction, a single 0.3 mg oral dose of clonidine hydrochloride (Catapres) was given to twelve patients with varying evidence of familial adrenal medullary hyperplasia and pheochromocytomas from kindreds with Multiple Endocrine Neoplasia type 2 syndrome (MEN-2), seven patients with sporadic pheochromocytomas and six normal subjects. Mean arterial blood pressure and plasma norepinephrine (NE) levels were lower than baseline values 2 h after clonidine in the normal subjects. Plasma epinephrine (E) rose in one normal but fell in the remainder after clonidine administration. In sporadic pheochromocytoma patients, E fell slightly in 4 and NE fell in 3 while mean arterial blood pressure was not significantly lower than baseline values in 7 patients 2 h after clonidine. In MEN-2, mean arterial blood pressure fell and there was a variable response of plasma E and NE to clonidine, which appears to be related to the presence of detectable anatomic (CT scan) and functional (131I-mlBG scintigraphy) abnormalities of the adrenal medulla. These findings are thus compatible with the spectrum of adrenal medulla dysfunction and the presumed development of pheochromocytoma in this syndrome.

Radioiodinated iodobenzylguanidines for diagnosis and therapy

Radiolabelled meta-iodobenzylguanidine has been one of the most successful of recent radiopharmaceuticals. In the short period of five years it has been shown to have high diagnostic sensitivity and specificity for many tumours of neuroectodermal origin. Furthermore its excellent concentration in many malignant tumours of this type offers a novel alternative treatment to those available at present.

Comparison of 131I-metaiodobenzylguanidine scintigraphy with urinary and plasma catecholamine determinations in the diagnosis of pheochromocytoma

In a retrospective study of 31 patients with suspected pheochromocytoma we examined the preoperative results of 131I-metaiodobenzylguanidine (131-I-MIBG) scintigraphy and a fluorimetric urine catecholamine determination test. An additional radioenzymatic plasma catecholamine determination test was performed in 25 patients. In 14 of the 31 patients the diagnosis of pheochromocytoma was later histologically confirmed. In the remaining 17 patients the suspected diagnosis was finally rejected after a clinical decision had been made on the basis of clinical history, symptoms, laboratory and imaging tests. 131-I-MIBG scintigraphy apparently had a very high specificity (no false-positive results among the patients with rejected diagnosis), but showed the least sensitivity (3 of 14 tumours were not detected). Urine catecholamines showed two false-negative and three false-positive results. Plasma catecholamines had the highest sensitivity and gave only one false-positive result. Because of its high pathognomonic value 131-MIBG scintigraphy can be helpful not only for localization, but also for confirmation of diagnosis when catecholamine determination tests are contradictory. On the basis of our experience with false-positive results after interfering medication therapy, urine and plasma catecholamine determination tests should only be carried out after purification with thin layer chromatography or high performance liquid chromatography.

Radio-iodobenzylguanidine for the scintigraphic location and therapy of adrenergic tumors

Radioiodinated meta-iodobenzylguanidine, a recently developed radiopharmaceutical, has been shown to permit safe, noninvasive, sensitive, and specific scintigraphic location of pheochromocytomas of all types. The technique is especially efficacious in the case of extraadrenal primary lesions and locally recurrent and metastatic tumors. In addition to being taken up by pheochromocytomas, meta-iodobenzylguanidine may be used to image neuroblastomas, nonfunctioning paragangliomas, and carcinoid tumors. Lesions with high 131I-meta-iodobenzylguanidine uptake may respond to treatment with large doses of this radiopharmaceutical.

New approach to the localisation of phaeochromocytoma: imaging with iodine-131-meta-iodobenzylguanidine

Thirty eight patients with known or suspected phaeochromocytoma were studied by radioisotope imaging after intravenous administration of iodine-131-meta- iodobenzylguanidine (131I- mIBG ), a radiopharmaceutical which has affinity for chromaffin tumours. Seventeen positive results (including one false positive) and 21 negative results (including two false negatives) were obtained. Clinical accuracy was 92%. Urinary noradrenaline concentrations were raised in all patients with confirmed phaeochromocytoma. These findings show that 131I- mIBG is of value in localising and assessing the extent of chromaffin tumours.