Localization of Metastases from Malignant Pheochromocytoma in Patients Undergoing 131I-MIBG Therapy with Manually Fused 123I-MIBG SPECT and CT Images

Can hybrid SPECT-CT overcome the limitations associated with poor imaging properties of 131I-MIBG?: Comparison with planar scintigraphy and SPECT in pheochromocytoma

OBJECTIVE

This study aimed to evaluate the incremental value of (131)I-MIBG hybrid SPECT-CT over planar scintigraphy (PS) and SPECT alone in patients with clinical or biochemical suspicion of pheochromocytoma.

METHODS

A total of 126 adrenals of 63 patients (mean [SD] age, 28.6 [15.7] years; male patients, n = 34; female patients, n = 29) with clinical or biochemical suspicion of pheochromocytoma were retrospectively evaluated. All patients had undergone (131)I-MIBG SPECT-CT of adrenal region. The PS, SPECT, and SPECT-CT images were independently evaluated by 2 nuclear medicine physicians with 6 years (R1) and 2 years (R2) experience and in separate sessions 1 week apart. A scoring scale of 1 to 5 was used, in which 1 is definitely abnormal, 2 is probably abnormal, 3 is indeterminate, 4 is probably normal, and 5 is definitely normal. Sensitivity, specificity, predictive values were calculated taking a score 2 or less as abnormal. With receiver operating characteristic (ROC) curve analysis, areas under the curve (AUC) were calculated for each modality and compared. Histopathology and/or clinical/imaging follow-up were taken as reference standard.

RESULTS

Of the 126 adrenals evaluated, 29 were indeterminate on PS for R1 and 48 for R2, 39 were indeterminate on SPECT for both, and on SPECT-CT, 1 was indeterminate for R1 and 2 for R2. SPECT-CT correctly characterized 28 of 29 indeterminate adrenals on PS and 37 of 39 indeterminate adrenals on SPECT for R1. Similarly, for R2, SPECT-CT correctly characterized 45 of 48 indeterminate adrenals on PS and 33 of 39 indeterminate adrenals on SPECT. On ROC comparison, PS was inferior to SPECT (P = 0.040 for R1; P < 0.001 for R2) and SPECT-CT (P = 0.001 for R1; P < 0.001 for R2) for both the observers. Moreover, SPECT was inferior to SPECT-CT for both the observers (P = 0.017 for R1 and P = 0.001 for R2). Accuracy of SPECT-CT (R1, 97.6%; R2, 97.6%) was higher than PS (R1, 91.2%; R2, 84.1%) and SPECT (R1, 94.4%; R2, 86.5%). Interobserver agreement was highest for SPECT-CT (κ = 0.966) as compared with PS (κ = 0.815) and SPECT (κ = 0.826).

CONCLUSIONS

I-MIBG hybrid SPECT-CT shows high sensitivity and specificity for characterizing adrenal lesions in patients with clinical or biochemical suspicion of pheochromocytoma and is superior to PS and SPECT alone. It will be especially useful in countries where (123)I-MIBG is not available.

Single photon emission computed tomography/computed tomography in the evaluation of neuroendocrine tumours: a review of the literature

The scintigraphic investigation of neuroendocrine tumours such as carcinoids has depended on standard techniques such as I-metaiodobenzylguanidine and In-pentetreotide imaging. More recently, the use of PET techniques such as Ga-DOTATATE has been advocated. An alternative improved modality is high-quality single photon emission computed tomography/computed tomography (SPECT/CT), which has the advantages of better sensitivity and specificity and has shown improved localization in up to 60% of cases. These advantages are especially true for pancreatic and lymph node lesions. Overall, SPECT/CT can result in a change in clinical management in 25% of patients. Although it is possible to combine SPECT and CT performed at different time points, there is better anatomical localization and improved reporter confidence when SPECT and CT are performed simultaneously.

Malignant pheochromocytoma metastasis to the breast shown on I-123 MIBG scan

A 36-year-old woman was referred to our department for I-123 metaiodobenzylguanidine (MIBG)-SPECT/CT scan 3 years after surgical excision of pheochromocytoma. She was referred due to recurrence of her symptoms as well as raised urinary catecholamines. Review of I-123 MIBG scan revealed multiple MIBG-avid metastatic lesions. Most of these were bony lesions, however, there were also 2 soft tissue lesions in the left breast. She subsequently underwent ultrasound-guided fine-needle aspiration of the left breast lesions. Fine-needle aspiration revealed cytologic changes consistent with pheochromocytoma. There has only been 1 previous reported case of pheochromocytoma metastasizing to the breast. This is the first case in which the metastasis was detected by I-123 MIBG scan.