MRI image of U-shaped fluid collection around the anus, showing perianal<unk>  formation. Diagnosis of<unk>  begins with a medical history and physical exam. Imaging studies which can help determine the diagnosis in cases of a deep non-palpable perirectal<unk>  include pelvic CT scan, MRI or trans-rectal ultrasound. These studies are not necessary, though, in cases which the diagnosis can be made upon physical exam. Classification<unk> es are classified according to their anatomic location and the following are the most common types; Perianal<unk> , Ischiorectal<unk> , Intersphincteric<unk>  and Supralevator<unk> . Perianal<unk> , which represents the most common type of<unk> es accounting for about 60% of reported cases, are superficial collections of purulent material just beneath the skin of the anal canal. Ischiorectal<unk>  is formed when suppuration transverses the external anal sphincter into the ischiorectal space. Intersphincteric<unk>  results from suppuration contained between the internal and external anal sphincters .Supralevator<unk>  forms from cephalad extension of the intersphincteric<unk>  above the levator ani or from caudal extension of a suppurative abdominal process like appendicitis, diverticular or gynaecologic sepsis. Differential diagnosis This condition is often initially misdiagnosed as hemorrhoids, since this is almost always the cause of any sudden anal discomfort. The presence of the<unk> , however, is suspected when the pain quickly worsens over one or two days and usual hemorrhoid treatments are ineffective in bringing relief. Furthermore, any serious<unk>  will eventually begin to cause signs and symptoms of general infection, including fever and nighttime chills. A physician can rule out a hemorrhoid with a simple visual inspection, and usually appreciate an<unk>  by touch.
Anorectal abscess
Pilonidal disease
Perianal cellulitis
Anal fissure
Perianal hematoma
Anal fistula
Rectal prolapse
Anal cancer