Clinical decision-making based on 11C-methionine PET in recurrent Cushing's disease with equivocal MRI findings.

OBJECTIVE

Diagnosis and accurate localization of recurrent tumors in Cushing's disease (CD) are challenging, especially after multiple transsphenoidal surgeries (TSSs) or radiosurgery. Even experts face difficulties in detecting these recurrent tumors, and a favorable surgical outcome is not guaranteed. In this report, the authors aimed to determine the usefulness of 11C-methionine positron emission tomography (MET-PET) for evaluating patients with recurrent CD with inconclusive magnetic resonance imaging (MRI) lesions and to develop a treatment protocol for these cases.

METHODS

In this retrospective study of patients with recurrent CD in the period between April 2018 and December 2022, the authors assessed the usefulness of MET-PET in determining whether equivocal MRI findings were recurrent tumors or postsurgical cavities and deciding further treatment options. All patients had undergone at least one TSS, and most had undergone multiple TSSs and had pathologically confirmed corticotroph tumors with hypercortisolemia.

RESULTS

Overall, 15 patients with recurrent CD (10 females and 5 males) were included, all of whom had undergone MET-PET. All patients had been subjected to multiple treatments, including TSSs or radiosurgeries. Their MRI scans demonstrated less-enhanced lesions that were not confirmed as recurrences even with cutting-edge MRI because they could not be distinguished from postsurgical changes with confidence. MET uptake was positive in 8 patients (9 examinations) and negative in 7. Following MET-PET, repeat TSS was performed in 5 patients. Corticotroph tumors were identified in all 5 patients, even though one of them had negative MET uptake. The MET uptake precisely identified a tumor location on the opposite side of the MRI-suspected lesion in 2 patients. Meanwhile, patients with negative uptake and mild hypercortisolism were only observed. Nonsurgical options were also used in other patients: temozolomide (TMZ) was administered in 2 patients owing to a prior history of multiple TSSs and radiosurgery and the drug-resistant nature of the disease. TMZ was highly effective in these patients; their Cushing's symptoms ameliorated, and their adrenocorticotropic hormone and cortisol levels continued to decline. Interestingly, MET uptake disappeared following TMZ treatment.

CONCLUSIONS

MET-PET is extremely useful for confirming equivocal lesions on MRI in patients with recurrent CD and for deciding further treatment options. The authors propose a novel protocol based on MET-PET results for treating patients with relapsing CD in whom the recurrent tumors cannot be confirmed with MRI.