You may have heard of phantom limb syndrome, a particularly odd condition that 80-100 percent of people experience after going through an amputation.

Amputees can experience sensations, discomfort, and pain that feels like it's coming from a limb or appendage that is no longer there. Though common after limb amputation, the condition can also affect people who have had other body parts removed, including breasts, tongues, penises, and even internal organs. In fact, if you can feel sensations in it pre-removal (we're looking at you, stomach and bladder) then it's possible to have phantom discomfort or pain in it after operation. 

This is true also of people who go through operations to have their rectum and colon removed (for instance following rectal cancer located low down in the rectum), leaving patients with a condition known as "phantom rectum syndrome".

"People who have lost a limb, still feel pain or itching or they feel like their limb's still there," BBC presenter Sam Cleasby, who runs the website So Bad Ass documenting her experience following a colectomy in 2013, told the BBC. "So that's the same but in your rectum. It's like your brain doesn't know that it's not attached anymore."

The syndrome affects somewhere between 32 and 68 percent of patients following rectum resection, and varies in its effects. Around half of people who experience it do so as pain, with others feeling sensations such as itching, feeling of feces in the rectum, an urge to defecate, feeling like your anus is contracting, feeling like you are passing wind, tightness, stinging, shooting pains, and pins and needles.

"I am only a few weeks out of surgery but I definitely get the old phantom rectum symptoms," Cleasby wrote on her website, "I really do think mine is my brain telling my body to do something it can't."

"For example, after a morning cup of coffee when you get 'that' urge, I still get that, but there is nothing down there. I can only poo through my stoma, I have no rectum or anus yet I get a real and true physical feeling that I need to pass stool through my butt."

The most common symptom in those with painful versions of the syndrome, according to a study on patients in China published in The Pain Clinic, was a dull pain. Two thirds of patients with painful phantom rectum syndrome said that it inhibited their daily activity.

So, what causes this strange syndrome? Unfortunately, like phantom pain affecting other removed body parts and limbs, it's not entirely understood, though it is believed to be partially explained by reorganization of the body map in the brain (aka "cortical reorganization") following amputation. 

Strangely, the syndrome does not affect patients at random. As well as phantom limb and phantom rectum pain being correlated to pre-amputation pain,  studies have found that people with higher levels of education are more likely to experience it, as well as people with more "rigid" personalities – or a resistance to changing behavior or attitudes.

Treatment of the condition follows similar lines to treatment of phantom limb syndrome, including analgesics, anticonvulsants, antidepressants, muscle relaxants, and cognitive behavioral therapy. The best method of dealing with it, however, might come from preventative action taken before surgery.

"It is proposed that the pre-amputation pain, a sustained noxious afferent input, causes the central neural sensitization which then may lead to the subsequent development of phantom pain," The Pain Clinic study explains. 

"Based on this notion, there have been several clinical studies which have demonstrated that pre-amputation epidural analgesia with local anesthetics and/or opioids may reduce the incidence of post-amputation phantom limb pain."