In general, rectal pressure is not related to the lumbar spine. There are some disorders that can cause this sensation such as sacral plexopathy (inflammation of the sacral nerves not related to compression or herniated discs) but compression of the lumbar nerves or cord issues are generally unrelated. There is a disorder called arachnoiditis (see website) that can cause this but again, the relationship between arachnoiditis and rectal pressure is not strong.
Dr. Corenman