Acute Internal Artery Thrombosis

The patient was an 86-year-old man with a history of mild dementia who presented with an acute onset of right hemiparesis.

This first image shows the swollen left hemisphere of the brain. Notice that the left cerebrum, in the distribution of the left middle cerebral artery, is swollen and slightly hemorrhagic. Superficial veins are engorged and have a slight yellow-white opacification on their edges. This material represents a cellular infiltrate - likely inflammatory cells.
The next image is taken from beneath the brain, from its inferior surface. It shows clot in the left internal carotid artery. Notice that the brain swelling extends to the left anterior frontal lobe, which indicates involvement of the left anterior cerebral artery, as well as the middle cerebral artery - a tip-off that the lesion is proximal to both of these vessels. The dilated left internal carotid artery "fits" with this scenario.
A close-up view shows the left internal carotid artery is dilated by the clot - compare it with the flat right artery. This dilatation indicates that the clot formed premortem, not post-mortem. Post-mortem clots (euphemistically called "chicken fat" for its rubbery but friable nature) do not dilate the vessel.
Finally, the extent of the infarction in the internal brain is demonstrated by the coronal section, showing extensive edema in the left cerebral hemisphere. Notice the changes in the high medial portion of the brain, within the distribution of the left anterior cerebral artery. Also, all portions of the basal ganglia at this level are involved, indicating the lesion is proximal, which again correlates with the known left internal carotid artery thrombus and subsequent infarction.

Click the image below to examine a virtual microscopic image of the thrombus:

In this view, some lines are present along the flow of the blood. The lines contain strands of inflammatory cells, mostly polymorphonuclear leukocytes. These lines, known as lines of Zahn, are better demonstrated in the Martius scarlet blue (MSB) stain in the following link:

In this stain, immature fibrin is yellow, more mature fibrin strands red, and mature, more compact fibrin blue. The lines contain various ages or compactions of fibrin mixed with erythrocytes and leukocytes. Like the growth rings of trees, they reflect the progressive build-up of fibrin and cellular material as the clot propagates and progressively closes off the artery.

Finally, a Musto-Movat stain demonstrates the structure of the artery, with its internal elastic lamina, as well as the lines of Zahn. Although this stain does not add a lot of new information, it is nevertheless esthetic and demostrates well the lines of Zahn.