Circulating tumour DNA (ctDNA) may serve as a measure of tumour burden and a useful tool for non-invasive monitoring of cancer. However, ctDNA is not always detectable in patients at time of diagnosis of metastatic disease. Therefore, there is a need to understand the correlation between ctDNA levels and the patients’ overall metabolic tumour burden (MTB). Thirty-two treatment naïve metastatic melanoma patients were included in the study. MTB and metabolic tumour volume (MTV) was measured by 18F-fluoro-D-glucose positron emission tomography/computed tomography (FDG PET/CT). Plasma ctDNA was quantified using droplet digital PCR (ddPCR). CtDNA was detected in 23 of 32 patients. Overall, a significant correlation was observed between ctDNA levels and MTB (p < 0.001). CtDNA was not detectable in patients with an MTB of ≤10, defining this value as the lower limit of tumour burden that can be detected through ctDNA analysis by ddPCR. We showed that ctDNA levels measured by ddPCR correlate with MTB in treatment naïve metastatic melanoma patients and observed a limit in tumour size for which ctDNA cannot be detected in blood. Nevertheless, our findings support the use of ctDNA as a non-invasive complementary modality to functional imaging for monitoring tumour burden.

We present the FDG and Ga DOTATATE PET/CT findings of a 68-year-old woman with pulmonary metastases 28 years after her initial diagnosis of central nervous system hemangiopericytoma. The largest of the pulmonary lesions showed prominent Ga DOTATATE uptake with comparatively minimal FDG avidity. Hemangiopericytoma is a rare mesenchymal tumor that arises from malignant pericytes, cells that form the walls of capillaries and postcapillary venules. This case demonstrates the potential of radiolabeled somatostatin analogs as a therapeutic option in the setting of widespread metastatic disease.

Objective: To illustrate the neuropsychiatric and imaging findings in a confirmed case of voltage-gated potassium channel antibody limbic encephalitis. Method: Case report and review of the literature. Results: A 64-year-old man presented with several months’ history of obsessive thoughts and compulsions associated with faciobrachial dystonic seizures. He had no significant past medical and psychiatric history. Physical examinations revealed only mildly increased tone in the left upper limb. Bedside cognitive testing was normal. Positron-emission tomography showed intense symmetrical uptake in the corpus striatum. No underlying malignancy was identified on whole body imaging. Magnetic resonance imaging, lumbar puncture and electroencephalogram were normal. Serum voltage-gated potassium channel antibodies were strongly positive. The patient had a favourable response to antiepileptic drugs, oral steroids and immunotherapy. Conclusions: Voltage-gated potassium channel limbic encephalitis characteristically presents with neuropsychiatric symptoms and temporal lobe seizures. Positron-emission tomography–computed tomography can be a useful adjunct to the clinical and biochemical work-up.

Laryngocele is an abnormal dilatation of the saccule of laryngeal ventricle, which is usually unilateral and filled with air or fluid. We present a case of bilateral laryngoceles colonized byAspergillusspecies.