Localization of a pheochromocytoma using I-123 MIBG adrenal scintigraphy.

S Shirkare, T Kuwert, M Weckesser, N Czech, KJ Langen, HW Muller-Gartner 
 Institut für Medizin, Forschungszentrum, Julich, Germany., Germany

Correspondence Address:
S Shirkare
Institut für Medizin, Forschungszentrum, Julich, Germany.
Germany

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::   Introduction

Pheochromocytomas are catecholamine-secreting tumours, originating in the adrenal medulla, which produce a highlyvariable clinical syndrome characterised by the triad of hypertension, headache and excessive perspiration[1]. Hypercatecholaminemia and similar disease states may also result from tumours developing outside the adrenal gland in the chromaffin tissue of the sympathetic or autonomic ganglia and paraganglia: such tumours are usually referred to as extra-adrenal pheochromocytomas or paragangliomas[2].

Pheochromocytomas are rare tumours with a prevalence of about 0.1%-0.5% in the hypertensive population, mainly occurring in the third or fourth decade[3]. In the patients with the clinical diagnosis and biochemical findings of pheochromocytoma, knowledge of the precise location of the tumor is important for planning surgical treatment[4].

Iodine-labelled metaiodobenzyiguanidine (MIGB) scintigraphy provides a specific method to localize pheochromocytombs. A case is reported here in whom scintigraphy was carried out and diagnosis was confirmed later on histopathogical examination of operatively removed tumour.

::   Case report

A 66-year old mate subject was referred for adrenal scintigraphy because of a one-year history of paroxysmal hypertension associated with paleness, tinnitus, dysarthria and nocturia.

His physical examination and ECG were unremarkable. The plasma concentration of norepinephrine (495 ng/I; normal range: 165-460) and the 24-hours urinary excretion of epinephrine (37 mg / 24 hours; normal range: 3-18) were elevated, whereas the plasma concentration of epinephrine and dopamine and the 24-hours urinary excretion of norepinephrine, dopamine and vanillyl mandelic acid (VMA) were within normal limits. Abdominal sonographic examination revealed a 5 cm x 4 cm tumour antero-medial to the left kidney. A CT scan of the abdomen disclosed-a 5 cm x 4.6 cm solid mass with a central necrosis in the region of the left adrenal gland.

Adital Scintigraphy: Potassium iodide (ten drops daily) was given three days before and two days after the imaging procedure. 370 M13q of 1-123 MIGB were injected intravenously. Imaging procedures were carried out twenty-four hours post-injection. Using a Trionix three head (TRIAD) gamma camera equipped with low-energy general purpose collimators, with the patient in supine position, the planar images of abdomen and thorax were obtained by collecting 500 k counts in posterior and both oblique views.

The images of the abdomen with posterior and oblique views revealed a focal tracer accumulation in the area of the left adrenal gland [Figure:1].

No tracer uptake in the right adrenal gland or in other areas was detected. Based on these findings, the diagnosis of a left-sided pheochromocytoma was made.

The patient subsequently underwent a left adrenalectomy and a 5.8 cm x 5.3 x 4.2 cm mass was removed. The diagnosis of pheochromocytorna was confirmed by histopathological examination.

::   Discussion

In this patient the pheochromocytoma was accurately located by 1-123 MIBG scintigraphy, as well as by the other imaging modalites. However, only MIBG scintigraphy provided the specific non-invasive information that the lesion was histologically a pheochromocytoma and that no other foci were present.

Although pheochromocytomas are uncommon, they still are of clinical significance because of their uncontrolled hypertension and morbidity[5]. However, they are a potentially curable cause of hypertension and accurate localization of the tumour is essential for management of the patient.

Various imaging techniques have been used for the detection and localization of pheochromocytomas such as ultrasonography, computed tomography and magnetic resonance imaging; these techniques play a major role before surgery[6],[7],[8],[9]. However, they frequently fail in detecting recurrent tumours at the sites of previous surgery, at extra-adrenal sites and in the evaluation of metastatic pheochromocytomas. Moreover, since about 10% of pheochromocytomas are bilateral, extra-adrenal or malignant, the detection of a single adrenal lesion does not exclude the possibility of the existence of other involved sites[11].

Procedures of nuclear medicine use metabolic markers directed toward specific tissues. The use of I-131 MIBG was introduced by Sisson, et al[12] in 1981 as a radiopharmaceutical for the diagnosis of pheochromocytomas.

I-131 MIBG is a marker for norepinephrine storage and shares the same mechanism of adrenergic tissue uptake as norepinephrine[13].

Several studies using this technique in the diagnostic work-up of patients with hypercatecholaminemia have been reported in the literature[14],[15],[16],[17],[18]. The reported sensitivity, specificity and predictive value are high as shown in [Table:1].

I-123-labelled MIBG is more suitable for scintigraphy by the gamma camera than I-131-labelled MIBG. The absence of beta-emission and its shorter physical half life of 13.2 hours (versus 8.1 days for I-131) permits a twenty-fold increase in initial radioactivity administered to the patient without increasing the absorbed radiation dose. This produces higher count rates and a better quality of images[19].

Velchik et al[9] reported that iodine-labelled MIBG scintigraphy is specific with respect to the physiological function and the initial localization procedure of choice due to ability of MIBG to screen the entire body with sharp contrast of the images, especially in detecting extra-adrenal diseases and at post-operative sites where anatomic planes were distorted. Thus, scintigraphy may act as a guide to direct CT and MRI both of which have superior spatial resolution for the depiction of anatomical detail.

::   Acknowledgment

We thank Dr D Scholz of the Malteser Krakenhaus, Julich for providing the clinical information.

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