Imaging of the anterior abdominal wall

98 Pages·2010·7.5 MB·English

Imaging of the anterior abdominal wall: A radiological review
Poster No.: C-1650
Congress: ECR 2010
Type: Educational Exhibit
Topic: GI Tract
Authors: S. P. Ramachandra, N. Gurjar, M. Bydder, S. Vessal; Stoke on
Trent/UK
Keywords: Abdominal wall, Inguinal canal, Umbilicus
DOI: 10.1594/ecr2010/C-1650
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Page 1 of 98
Learning objectives
1. Revise the anatomy of the anterior abdominal wall (AAW).
2. Describe and illustrate the imaging findings of abdominal wall
pathologies.
3. Discuss the appropriate imaging techniques and their limitations used to
diagnose commonly occurring anterior abdominal wall lesions.
Background
The AAW forms a flexible sheet of tissue across the anterior and lateral abdomen,
has an important role in maintaining the form of the abdomen, and provides a barrier
between the peritoneal cavity and the exterior. It forms the inguinal canal, umbilicus,
both of which are of considerable clinical importance. Pathological processes affecting
the AAW can be grouped into hernias, infections & abscesses, inflammatory lesions
including endometriomas & fistulas, traumatic or spontaneous haematomas and tumours
both benign and malignant.
Multimodality imaging is often required to assess these pathologies. Ultrasound is a
st
useful simple 1 line investigation but is limited by its inability to visualise the full extent
of pathology and its relation to adjacent structures. CT is commonly used, but MRI
has superior soft tissue resolution, multi-planar capability and lack of radiation and is
a particularly useful modality especially in younger patients and in cases of suspected
primary neoplasms.
Page 2 of 98
Imaging findings OR Procedure details
Anterior abdominal wall extends from the xiphoid and lower six costal cartilages to the
anterior aspect of pelvic bones. It is composed of several layers including skin, superficial
fascia, subcutaneous fat, anterolateral and midline muscle groups, transversalis fascia,
extraperitoneal fat and peritoneum. The superficial fascia is a single layer containing
variable amount of fat. Inferiorly it is divided into two layers, thick superficial fatty layer
and deep membranous layer, between which run neurovascular bundles and lymphatics
(Fig 1-2). on page 48There are four muscles in the anterior and lateral abdominal
wall. Anteriorly there are paired rectus abdominis muscles. Superficial to deep, the three
muscles which make up the anterolateral surface are external oblique, internal oblique
and transversus abdominis (Fig 3). Presence of fat in between allows the individual
muscles to be identified at CT and MRI (Fig 3 on page 49).
Inguinal ligament is a thick band and is formed by the aponeurosis of external oblique
muscle between the anterior superior iliac spine and pubic tubercle. Medially, the inguinal
ligament falls short of the pubic tubercle and attach to the pectineal line as lacunar
ligament which forms the medial boundary of the femoral ring, through which a femoral
hernia can descend (Fig 2).
Inguinal canal is a short, diagonal passage measuring about 4cms in length. This has
2 openings, deep and superficial inguinal rings. The deep inguinal ring is lateral to the
inferior epigastric vessels and superficial inguinal ring is a hiatus in the aponeurosis of
external oblique muscle, lying supero-laterally to the pubic crest. It transmits spermatic
cord in males, round ligament in females and ilio-inguinal nerve in both.
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Fig.: The image shows the 4 abdominal wall muscles and the the fascial layers.
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
Page 4 of 98
Fig.: This image depicts the anatomy of the inguinal region and the hernial sites.
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
Page 5 of 98
Fig.: Axial CT showing the anterior abdominal wall muscles surrounded by
subcutaneous fat and skin.
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
Tumours -Benign tumours - Desmoids, Lipomas, leiomyomas
Malignant tumours - Direct tumour spread, haematogenous
metastasis, sarcomas, Lymphomas
Infections
Inflammatory lesions - Endometriomas, fistula/ sinuses,
Others - AVMs / portosystemic shunts, vascular grafts,
haematomas, hernias, implants.
The benign tumours of the abdominal wall are more common than the malignant
neoplasms. Metastasis (Fig 4a) on page 50 (fig 4b on page 51)account for most
Page 6 of 98
of the malignant lesions found in the abdominal wall, although primary sarcomas or
lymphomas may also develop. Pancreatic and lung tumours are the most common
neoplasms that metastasise to the abdominal wall. Sister Mary Joseph`s nodule (Fig
4a) on page 50 is referred to as the metastasis of visceral malignancy to umbilicus,
commonly from the gastrointestinal or genitourinary tract.
Fig.: Post contrast Axial Ct abdomen demonstrating large metastasis from ovarian
carcinoma. The smaller mass is inflitrating into the umbilicus - "Sister Mary Josephs
Nodule"
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
Page 7 of 98
Fig.: Metastatic melanoma - Enhancing soft tissue nodules along the external oblique
muscle on the left.
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
Desmoids are now included in deep fibromatosis and are histologically benign but locally
aggressive tumours. Although they are rare, they are a common manifestation of Gardner
rd th
syndrome. They are common in 3 and 4 decade and females are affected more
commonly. They are locally aggressive tumours with invasion of contiguous structures
with high incidence of local recurrence despite apparent complete surgical removal.
Lipomas (fig 4c) are the most common soft tissue neoplasm and are much more frequent
than liposarcomas. These can be categorized as superficial or deep. In the abdomen and
trunk, superficial lipomas are more common and are generally less than 5cms. The deep
lipomas are usually large at presentation and imaging is often required. On Ultrasound
the lipomas appear as hyperechoic mass and the capsule is usually difficult to see.
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CT and MRI are superior in providing a confident diagnosis. CT and MRI reveal a mass
of homogenous adipose tissue similar to the surrounding normal fat. They can have thin
internal septa and do not enhance after intravenous contrast administration. In many
cases MRI can be used to make a confident diagnosis.
Fig.: Axial and Coronal reconstructions showing Lipoma between the Transversus
abdominis and internal oblique muscles.
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
Page 9 of 98
Fig.: Axial and Coronal reconstructions showing Lipoma between the Transversus
abdominis and internal oblique muscles.
References: S. P. Ramachandra; Radiology, University hospital of Northstaffordshire,
Stoke on Trent, UNITED KINGDOM
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