This is an interesting case of anorectal signet ring carcinoma with first presentation of an early stage disease, showing the aggressive disease and the undetectable behavior of this type of histology which can mislead diagnosis. Brain/CNS metastasis from colorectal cancer (CRC) is rare occurring in 3% of cases, and leptomeningeal carcinomatosis (LMC) is extremely rare in CRC (<0.02%). Symptoms and signs of LMC are pleomorphic and may be localized to three compartments: cerebral hemispheres, cranial nerves, and spinal cords and roots. Treatment of metastatic rectal cancer has been improving over the last few years with a lot of changes toward longer survival and improvement in quality of life and to change the disease into a chronic condition. However, in our case, the overall survival from the onset of LMC was 3 weeks only. Revising the evidence in the treatment of signet ring histology of rectal cancer, there is no specific treatment recommendation that is for this histology and for such very aggressive behavior which could be considered as a separate entity to the classic adenocarcinoma histology.