Within the mediastinum there is an area of activity on the coronal PET-CT images. This does not correspond to a typical nodal station. Coronal and axial images demonstrate that this is within the region of the interatrial septum. There is a proliferation of fat in the inter-atrial septum. This is benign inter-atrial lipomatous hypertrophy. The fat in this region can have hyper-metabolic brown fat properties much like fat in the root of the neck. Metastatic disease can spread through this region, however, only in contiguous locally advanced intra-pericardial tumours.
This case should have been no challenge to those paying attention to earlier cases (see January 2016 cases , Case to Ponder Number 52 for more information: