The radiological signs that can be seen on abdominal imaging discussed here are: apple core lesion,
coffee bean sign,
cottage loaf sign,
donut sign and omental cake.
For each sign a detailed description is provided,
accompanied with illustrations and possible differential diagnoses.
APPLE CORE LESION
An apple core lesion is the radiological manifestation of a focal stricture of the bowel at contrast material enema examination.
The stricture demonstrates shouldered margins and resembles the core of an apple that has been partially eaten (Fig.
1).
The most common cause of this apple core appearance is an annular carcinoma of the colon.
The apple-core lesion of colon may be caused by a variety of diseases,
such as adenocarcinoma, infection ,
inflammatory colitis,
ischaemic colitis,
endometriosis,
lymphoma with colonic involvement,
and sequela of radiotherapy treatment.
Severe colonic lumen narrowing leads to bowel obstruction .
These differentials should be kept in mind and correlate with clinical manifestations to avoid misdiagnosis.
COFFEE BEAN SIGN
The coffee bean sign is seen on an abdominal radiography as an area of hyperlucency that resembles the shape of a coffee bean.
It is a classic conventional radiographic finding of sigmoid volvulus (up to 80 % of sigmoid volvulus cases can be diagnosed by viewing the conventional abdominal radiograph alone).
As the closed loop of the sigmoid colon distends with gas the medial walls of the dilated bowel form the cleft of the coffee bean,
while the lateral walls of the bowel form the outer walls of the bean.
Since the volvulus is located at the sigmoid colon,
the coffee bean arises from the pelvis and sometimes it may be very big and occupy the entire abdomen.
The apex of the coffee bean is usually located above the level of T10 vertebra and can extend to the left or right of the midline (Fig.
2).
COTTAGE LOAF
Cottage loaf is a traditional English type of bread.
Its main characteristic is its shape,
with two round loaves,
one on top of the other,
with the upper one being rather small.
In radiology the cottage loaf sign is related to a specific radiographic appearance of diaphragmatic rupture seen mostly on CT scans.
This sign can be seen in right-sided diaphragmatic rupture with partial herniation of the liver through the diaphragmatic defect.
The herniated component is separated by a waist at the diaphragm from the larger intra-abdominal component and therefore it resembles the two round loaves with one smaller loaf above the diaphragm and the bigger one under the diaphragm (Fig.
3).
The best way to spot the cottage loaf sign is to carefully analyse the coronal and sagittal scans,
especially in trauma patients.
DONUT SIGN
The donut (also spelled doughnut) is popular in many countries throughout the world and prepared in various forms.
Important for radiology is the one in the form of a ring,
which also happens to be the most common donut type in the United States.
The donut sign (also known as target sign or bull's eye sign) can be seen on ultrasound and CT scans in intestinal intussusception.
On transverse scans the shape of ring donut is mimicked by the hyperechoic central core of bowel and mesentery surrounded by the hypoechoic outer edematous bowel (Fig.
4).
On longitudinal imaging,
intussusception resembles another popular food; a sandwich.
Moreover,
the donut sign can be related to circumferential thickening of the bowel wall in colon carcinoma or an inflammatory bowel disease with appearance that resembles a donut on CT scan.
The inspiration from donuts in radiology has affected the pediatric imaging as well.
In pediatric radiology the donut sign is related to hypertrophic pyloric stenosis since the transverse ultrasound scans in this disease can also resemble the ring donut.
OMENTAL CAKE
Omental cake refers to infiltration of the omental fat by material of soft-tissue density seen on CT scans.
Anteriorly,
this soft tissue density in omental fat gives the appearance of cream over the cake,
called omental caking (Fig.
5).
The etiology of soft-tissue density infiltration is various and ranges from inflammation,
infection to malignancy. Malignancy can either be a primary tumor of omentum,
or spread from the adjacent or remote areas.
The most common cause of this radiological cake (or omental caking) are metastases from ovarian, gastric,
or colon cancer.