Grade I & II are simpler fistulas and can be managed by Fistulotomy whereas Grade III-V are complex fistulas in which fistulotomy should be not be done. They should be managed by Fistula experts. Unlike Parks and St James University Hospital Classification, this correlation is quite accurate with Gargs classification. Therefore this new classification is useful to both surgeons and radiologists. Types
Depending on their relationship with the internal and external sphincter muscles, fistulae are classified into five types:

Extrasphincteric fistulae begin at the rectum or sigmoid colon and proceed downward, through the levator ani muscle and open into the skin surrounding the anus. Note that this type does not arise from the dentate line (where the anal glands are located). Causes of this type could be from a rectal, pelvic or supralevator origin, usually secondary to Crohns disease or an inflammatory process such as appendiceal or diverticular abscesses. Suprasphincteric fistulae begin between the internal and external sphincter muscles, extend above and cross the puborectalis muscle, proceed downward between the puborectalis and levator ani muscles, and open an inch or more away from the anus. Transphincteric fistulae begin between the internal and external sphincter muscles or behind the anus, cross the external sphincter muscle and open an inch or more away from the anus. These may take a U shape and form multiple external openings. This is sometimes termed a horseshoe fistula. Intersphincteric fistulae begin between the internal and external sphincter muscles, pass through the internal sphincter muscle, and open very close to the anus.
These subtypes are described below:

lepidic predominant 
acinar predominant 
papillary predominant 
micropapillary predominant 
solid predominant with mucin production Cell patterns identifying subtypes are associated with prognosis, ranging from favorable (lepidic) to intermediate (acinar and papillary) to poor (micropapillary and solid).Four discrete variants of invasive adenocarcinomas not assignable to these five subtypes are also included in the current classification:

invasive mucinous adenocarcinoma 
colloid adenocarcinoma 
fetal adenocarcinoma 
primary pulmonary enteric adenocarcinoma

Imaging
A chest x-ray (radiograph) is often the first imaging test performed when a person presents with cough or chest pain, particularly in the primary care setting. A chest radiograph may detect a lung nodule/mass that is suggestive of cancer, although sensitivity and specificity are limited.CT imaging provides better evaluation of the lungs, with higher sensitivity and specificity for lung cancer compared to chest radiograph (although still significant false positive rate). Computed tomography (CT) that is specifically aimed at evaluating lung cancer includes the chest and the upper abdomen. This allows for evaluation of other relevant anatomic structures such as nearby lymph nodes, adrenal glands, liver, and bones which may show evidence of metastatic spread of disease. Indeed, the US Preventative Services Task Force recommends annual screening with low-dose CT in adults aged 55 to 80 years who have a 30 pack-year smoking history and currently smoke or have quit within the past 15 years, with certain caveats (see Lung cancer screening).Nuclear medicine imaging, such as PET/CT and bone scan, may also be helpful to diagnose and detect metastatic disease elsewhere in the body.