What Does This Image Reveal?

Abdominal tenderness in an older woman

A 67-year-old woman who is being treated as an inpatient for head traumacomplains of vague tenderness during an abdominal examination. Othercomplaints are difficult to assess. She had been placed on an oxygen ventilator;however, her cognitive function and pulmonary function are improving, andher cerebral edema is diminished.The patient has hypertension, diabetes, moderate chronic obstructivepulmonary disease, and severe peripheral vascular disease. Her temperature is37.7

^o

C (100

^o

F).You order a radiograph of the chest. What abnormality is evident here,and what further investigation is warranted?

Abdominal tenderness in an older woman

The supine radiograph of thechest reveals a small lucency belowthe right hemidiaphragm that is consistentwith free intraperitoneal gas(

A,

yellow arrow). A small pleuraleffusion in the right lung is also noted(

A,

black arrow). (A nasogastric tubethat runs the length of the esophagusis visible as well, although its end isnot shown.) The small lucency belowthe right hemidiaphragm is a newfinding; it was not visible on a radiographobtained the day before (

B

).An abdominal radiograph is obtainedwith the patient in the left lateraldecubitus position. This secondfilm confirms the presence of free intraperitonealgas superficial to theright lobe of the liver (

C,

arrow).To identify free intraperitonealgas in the abdomen, a radiographthat shows an air-soft tissue interfaceis needed. In the upright radiographhere, this interface was created whenthe air rose to the least dependentportion of the abdomen. In the frontalradiograph obtained with the patientin the left lateral decubitus position,the air was again seen in the least dependentportion of the abdomen--inthis case, between the right lateralbody wall and the liver.The second radiograph is helpfulbecause it shows that the air in theabdomen shifts position; this finding can rule out air in an abscess and airin the bowel wall (pneumatosis intestinalis).In addition, the use of 2 imagescan help prevent mistaking intraperitonealgas for a subdiaphragmatic dilatedloop of bowel or basilar lung bullae--2 common diagnostic pitfalls.This patient has not had any recentabdominal interventions thatmight explain the presence of free intraperitonealgas. It is extremely importantto obtain a complete clinicalhistory in this setting. Very often, arecent intra-abdominal interventionexplains the finding.When there is no history of interventionto explain the existence offree intraperitoneal gas, interpret thefinding in the light of the patient'ssymptoms and laboratory results. If apatient is asymptomatic, has no fever,and has a normal white blood cell(WBC) count, suspect a benign causesuch as:

• Extension of air below the diaphragmfrom pneumomediastinum orpneumothorax.
• Perforated jejunal diverticulitis.
• Pneumatosis cystoides intestinalis.
• Occasionally, the aftereffects of gynecologicmanipulation.

When abdominal tenderness,fever, and an elevated WBC count arepresent, suspect a perforated viscus.Common causes of perforated viscusinclude peptic ulcer disease, ruptureddiverticulum of the colon, inflammatorybowel disease with perforation,and small bowel obstruction/ischemiawith perforation. A less commoncause of free intraperitonealgas--but one worth consideration--is infection of the peritoneum by gasproducingorganisms.In this patient, a CT scan confirmsthe presence of

free intraperitonealgas

superficial to the liver (

D,

arrow). A more inferior slice (

E

) revealsthe gas (white arrow) and alsoshows the pyloric region to be unremarkable(yellow arrow). A still moreinferior slice shows bowel wall thickeningof the colon in the region of thehepatic flexure (

F,

arrow).Based on the CT findings, a definitivediagnosis of free intraperitonealgas is made. Based on the presenceof free gas and of bowel wallthickening, the cause is presumed tobe

diverticulitis.

Outcome of this case.

Becausethe patient was a poor surgical candidate,she was given a trial of aggressiveantibiotic therapy. This proved tobe successful; her symptoms wereameliorated and no further sequelaewere identified.