The abdominal wall pathology can mainly be classified into 4 categories – presence of bowel,
solid lesion,
fluid collection/cystic lesion and vascular lesion.
Presence of bowel
Hernia is one of the most common abdominal wall lesions.
It is the protrusion of abdominal content through abdominal wall weakness or defect,
of which the defect can sometime be visualized.
The most common herniated contents are omentum,
fat and bowel loops.
Ultrasound can provide real time assessment upon Valsalva maneuver and standing position to demonstrate induction and reducibility of hernia contents.
The bowel loops in the herniated sac may become strangulated,
especially for the irreducible hernia.
Ischemic or strangulated bowel loops can show bowel wall thickening and absence of peristalsis in ultrasound.
There are several types of hernia.
Inguinal hernia is the most common type,
which is located superior to inguinal ligament.
There are two subtypes – direct and indirect inguinal hernia.
The direct type is the protrusion of content through a defect in external oblique aponeurosis (superficial inguinal ring).
It is located medial to the inferior epigastric artery and within the Hesselbach triangle (Fig. 1).
The indirect type is more common than direct type.
It is the protrusion of content through a defect in transversalis fascia (internal inguinal ring) into the inguinal canal.
As internal inguinal ring is located lateral to the inferior epigastric artery,
this can be discriminated from direct type.
(Fig. 2 and Fig. 3) Scrotal extension can be demonstrated in indirect inguinal hernia (Fig. 4),
whereas it is very uncommon in direct type.
Femoral hernia is less common and has a female predilection.
It is protrusion of hernia content into the femoral sac,
which is the empty sac located medial to ipsilateral femoral vein and inferior to ipsilateral inguinal ligament.
(Fig. 5 and Fig. 6)
Other common types of hernia include incisional hernia at previous operative site (Fig. 7 and Fig. 8) and ventral hernia in midline epigastrium due to defect in linea alba (Fig. 9).
Solid lesion
Solid lipomatous lesions are commonly non-aggressive in nature,
such as lipoma,
subcutaneous panniculitis and herniated fat.
Abdominal wall lipoma is usually encapsulated and situated in subcutaneous region.
Its sonographic appearance can be hypoechoic,
isoechoic or mildly hyperechoic in comparison with surrounding fat (Fig. 10).
It is similar to the lipoma in the rest of the body.
Subcutaneous panniculitis is inflammation of subcutaneous fat.
It can be localized and presented as a painful nodule with focal increase in echogenicity of subcutaneous fat at corresponding area (Fig. 11).
For non-lipomatous solid lesion,
benign lesions such as neurofibroma (Fig. 12 and Fig. 13) and aggressive lesions such as metastatic deposits in abdominal wall (Fig. 14) could sometimes demonstrate similar sonographic appearance.
Well defined border,
homogeneous echogenicity and absence of vascularity cannot completely exclude malignancy.
Interval follow up scan for monitoring lesion size can be considered.
Histological examination may be required if high suspicious of malignancy.
However,
in some scenario,
possible diagnosis should be suggested.
1.
Umbilical nodule with history of malignancy in particular gastrointestinal and gynecological origins, Sister Mary Joseph nodule (metastatic deposit) has to be considered.
2.
Scar endometriosis as an ill-defined hypoechoic lesion at previous operation scar (in particular gynecological operation) in female patients.
Cyclical nature of symptoms and variable sizes supports the diagnosis (Fig. 15).
3. In male patient with absence of testis,
isolated small hypoechoic ovoid lesion in the ipsilateral groin (~75-80% in inguinal canal) without echogenic hilum supports the diagnosis of undescended testis.
Testicular parenchyma evaluation is crucial due to potential risk of malignant transformation (Fig. 16).
4.
Hypoechoic inguinal lymph nodes with distorted architecture are suspicious of malignant involvement.
They are commonly seen in lymphoma and malignancy with expected lymphatic drainage pathways across inguinal nodes such as lower limb malignant tumor (Fig. 17).
5. Everted xiphisternum can be mistaken as an epigastric mass and presented as a painless hard lesion,
which can be confirmed with ultrasound (Fig. 18).
Fluid collection/cystic lesion
Anechoic fluid collection in the abdominal wall can be sterile such as seroma or inflammatory in nature such as abscess.
Seroma can be seen adjacent to post-operative wound,
in particular after hernia mesh repair (Fig. 21).
Abscess can be due to haematogenous spread or contagious infection such as severe cellulitis (Fig. 19 and Fig. 20).
Inflammatory fluid collection or abscess along the Tenckhoff catheter exit site in peritoneal dialysis patients is one of the common examples in daily practice (Fig. 22).
Rectus sheath haematoma is clinically important.
It is usually due to inferior epigastric artery injury. Patients with bleeding tendency such as leukemia,
coagulopathy or taking anti-platelet / anti-coagulation medication are at risk.
Subtle trauma or injury such as severe coughing can result in this condition.
Early identification may alter patient management such as reversal of deranged clotting profile or possible interventional embolization if ongoing bleeding (Fig. 23).
The sonographic echogenicity depends on the chronicity of the haematoma.
It is likely mixed hyper-/isoechoic and hypoechoic in acute stage and becomes more hypoechoic when lesion ages.
The haematoma is commonly ovoid within the rectus sheath,
which is confined to ipsilateral sheath above the arcuate line and may spread across midline below this line.
Urachus is a congenital urachal remnant between umbilicus and urinary bladder.
It is usually diagnosed in pediatric patients.
Urachus can be presented in form of cyst,
sinus or fistula.
It usually remains asymptomatic unless infection or bleeding complication occurs
Urachal cyst appears anechoic and sometime faint internal echoes can be seen (Fig. 24).
Urachal sinus or fistula is commonly presented as a thickened tubular structure along the midline below the umbilicus.
Differentiation between two can sometimes be difficult as the opening may be subtle and not well visualized in ultrasound scan (Fig. 25).
Hydrocele of spermatic cord is occasionally presented as an inguinal mass in male patient.
It is shown as a well-demarcated anechoic lesion along the spermatic cord,
superior and separated from ipsilateral testis and epididymis (Fig. 26).
Vascular lesion
Vascular lesion is a relatively uncommon entity in abdominal wall.
Subcutaneous haemangioma can be presented as an area with multiple tiny ill-defined hypoechoic lesions in an echogenic hypervascular background (Fig. 27 and Fig. 28).
Pseudoaneurysm in the groin region is not uncommon,
usually in needle drug addicts or iatrogenic from arterial puncture.
There is extravasation from femoral artery into the surrounding tissues.
It forms a potential space and communicates with the injured portion of femoral artery.
Pulsation and possible swirling of echogenic blood can sometimes be seen in the potential space during real time scan,
with classical yin-yang sign in Doppler examination due to turbulent flow (Fig. 29, Fig. 30 and Fig. 31).
Saphenous varix is serpentine dilatation of saphenous vein draining into the saphenofemoral junction.
It is anechoic in gray scale ultrasound and may demonstrate size change upon Valsalva maneuver,
mimicking femoral hernia due to similar anatomical location.
However,
it can easily be distinguished from femoral hernia with presence of venous flow signal in Doppler study (Fig. 32 and Fig. 33).