COMMENTARY

Free intraperitoneal
air on paediatric

plain radiographs
and differentiating

this from a 'food
mound'

T he detection of free intraperito-
neal air is an important indicator of a
perforated hollow viscus}which has a
variety of causes in childhood. There
are also}however} numerous causes of
a pneumoperitoneum in children that
may not be due to a perforated hol-
low viscus. These may be differenti-
ated by their clinical setting. On oc-
casion a child with a perforated viscus
may show pneumoperitoneum on ra-
diographs} but have none of the clas-
sical features of an acute abdomen
clinicallyl-' It is in such situations that
the surgeon may rely on the radiolo-
gist's findings. There are also situations

where pneumoperito-
neum is seen as a sur-
prise finding on chest
radiographs performed
for intrathoracic dis-
ease (e.g. pneumome-
diastinum).

The best known X-
ray finding of free intra-
peritoneal air is free
subphrenic air seen on
an erect chest film. This

SAndronikou
MBBCh (WIts), FCRadDiag (SA), FRCR (London)

eWelman
MBChB

E Kader
MBChB

Department of Paediatric Radiology,
Universily of Gape Town and Institute of Child Health,

Red Cross War Memorial Children's Hospital,
Rondebosch, Cape Town

Corresponding author
S Andronlkou

Department of Paediatric Radiology, Red Cross War
Memorial Children s Hospital, Cape Town, 7700

Tel: (021) 658·5422. Fax: (021) 658·5101.
E-mall;docsav@mweb.co.za

Figure 1: Erect film showing right subphrenic free air (arrow)

29 SA JOURNAL OF RADIOLOGY· February 2001

is especially so when noted on the
right above the liver (Figure I)} but
also when situated between the dia-
phragm and stomach (Figure 2).1

Figure 2: Erect film showing both right and left
subphrenic free air (arrows)

More difficult is the detection of free
air on a supine film where air may
present around the falciform ligament
(Figure 3) or in the subhepatic space

Figure 3: Supine film with free air outlining the
falciform ligament (arrowheads)

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Free intraperitoneal air on paediatric
plain radiographs and differentiating
this frorn a 'food mound'

from page 29

Figure 9: Horizontal beam supine film shows
the free air just deep to the anterior surface
with a visible "Rigler's" sign (arrow)

Figure 5: The "Rigler's" sign, with air outlining both
sides of the bowel wall (arrows)

(Figure 4) or may delineate both sides
of the bowel wall as the "Rigler's sign"
(Figure 5).1,2 Larger volumes of air
may be seen as the "lucent liver sign"
(Figure 6) and small children may
show large amounts of free intraperi-
toneal air as the "football" sign (Fig-
ure 7).1 A decubitus film with the
right side up (Figure 8) and a hori-

zontal beam shoot-through (Figure 9)
are useful techniques for identifying
free airY especially in the leu set-
ting.

Every so often we are shown a ra-
diograph like Figures 10 or II, where
there is suspicion of free air under the
left hemidiaphragm. These radio-
graphs are deceptive in the erect po-
sition, as a specific food type or con-
sistency may result in what we have
termed the "food mound" sign. Food

Figure 8: Lateral decubitus film with the right side up,
showing free air around the lateral aspect of the liver (arrow)

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30 SA JOURNAL OF RADIOLOGY. February 2001