We had a bit of a hiatus in KCC for the last couple of weeks with the residents preparing for written boards, and various people being away. But tonight we reconvened to do some alternate imaging cases, including CT and MR.
One case was a dog with an extra-axial, broad-based, strongly contrast-enhancing mass in the left skull base that was compressing the brain stem. On the GRE images, there was focal loss of signal from susceptibility artifact due to hemorrhage. We all agreed that the strong contrast enhancement meant the mass was extra-axial, since it would be outside the blood-brain-barrier. Normal brain does not contrast enhance, which brought up the question of whether an intra-axial mass could enhance similarly. Key points included the fact that an intra-axial mass enhances because of new blood vessel recruitment, and that higher grade gliomas enhance more strongly than low grade gliomas. The difference between an extra-axial mass and intra-axial mass would be uniformity of enhancement; gliomas tend to be heterogeneously enhancing, while meningiomas are more uniformly enhancing.
Another point that this case brought up was the different ways of looking for hemorrhage on MR. On spin-echo sequences, there are changes in intensity on T1 and T2 sequences as the blood degrades into hemoglobin derivatives over time. This often gives a mottled appearance. With GRE sequences, there is a signal void, or black area, where the degradation products from blood are located.
A second interesting case was a CT of a stray dog with mild hind limb lameness. There was a focal, soft tissue and mineral attenuating mass in the medulla of the proximal femur. It appeared to arise from the endosteum and expand into the medulla, and had a mineralized capsule with a broad base that blended back into cortical bone. There was some cortical thinning but no disruption. It had mostly benign characteristics and appeared to be arising primarily from bone. Benign primary bone tumors would include osteoma, osteochondroma, and enchondroma. This one turned out to be an osteoblastoma; very rare and luckily benign.
That’s all for this episode. KCC is winding down for the summer, but we may get to look at a few more cases before the end of the quarter.