A 2000 year old Egyptian mummy was found with clear blood vessel imprints on its skull. A part of a male's brain or meninges was pressed up against his skull, in the perfect conditions, allowing for the vessels to be imprinted on the skull. It was easy to tell the pattern and size of the vessels. Even though the brain is usually removed during mummification, it if believed that improper cleaning lead to the meninges staying intact, which allowed for the imprint. This is an extremely rare case as researchers usually do not see blood vessel imprints.
The mummy was preserved using bitumen. Usually, the brain in removed through the nasal cavity, then the cranial cavity is cleaned with chemicals so it is very unlikely for anything to stay intact. In this case it is possible that a part of the brain was left intact, leading to the imprint.
A study was done in 2010 with details about the mummy and its intact brain vessels. The study was done by Albert Isidro, Luis M. Gonzálvez and Adrià Arboix.
Several mummies were found along side this one. Researchers had interest in this one because of the pattern on its skull. They then chose to further investigate and found the vessel imprints.
Griggs, M. (2014). Blood Vessels Left Imprint on 2,000 Year Old Mummy. Smithsonian. Retrieved 18 March 2017, from http://www.smithsonianmag.com/smart-news/blood-vessels-left-imprint-2000-year-old-mummy-180952882/
Isidro, A., Gonzálvezb, L., & Arboixc, A. (2010). Brain vessels mummification in an individual of ancient Egypt. Sciencedirect.com. Retrieved 18 March 2017, from http://www.sciencedirect.com/science/article/pii/S0010945214002950
Sinpetru, L. (2014). This 2,000-Year-Old Mummy's Brain Left Imprints on the Inside of His Skul. Softpedia. Retrieved 18 March 2017, from http://news.softpedia.com/news/This-2-000-Year-Old-Mummy-s-Brain-Left-Imprints-on-the-Inside-of-His-Skull-460403.shtml