Same as bowel obstruction
Labs:
CBC: significant leukocytosis may indicate sepsis/gangrene/perforation
Electrolyte Panel: guides rehydration
Imaging: See Clinical Features above
Abdominal Xray
distended colon
small bowel distension possible
cecal diameter >12cm indicates high risk of perforation
CT
dilation of the large bowel, often without an abrupt transition point
no mechanically obstructing lesion
gradual transition point is commonly identified at or near the splenic flexure
Water soluble contrast enema
diagnostic: rules out mechanical obstruction
may also be therapeutic
Colonoscopy: also diagnostic and therapeutic
CBC: significant leukocytosis may indicate sepsis/gangrene/perforation
Electrolyte Panel: guides rehydration
Abdominal Xray
distended colon
small bowel distension possible
cecal diameter >12cm indicates high risk of perforation
CT
dilation of the large bowel, often without an abrupt transition point
no mechanically obstructing lesion
gradual transition point is commonly identified at or near the splenic flexure
Water soluble contrast enema
diagnostic: rules out mechanical obstruction
may also be therapeutic
Colonoscopy: also diagnostic and therapeutic
distended colon
small bowel distension possible
cecal diameter >12cm indicates high risk of perforation
dilation of the large bowel, often without an abrupt transition point
no mechanically obstructing lesion
gradual transition point is commonly identified at or near the splenic flexure
diagnostic: rules out mechanical obstruction
may also be therapeutic
Ogilvie's syndrome
Malignancy 
Dressler's syndrome
Diverticular disease
Fitz-Hugh-Curtis syndrome
Compression from metastatic disease
Mallory-Weiss tear
Impaction