Abdominal Wall Disorders: Diagnostic Testing

Definition / Overview

Accurate diagnosis of abdominal wall pathology requires a structured approach integrating clinical assessment with targeted investigations. The spectrum of abdominal wall disorders presenting to a general surgeon includes:

• Primary and incisional hernias (inguinal, femoral, umbilical, epigastric, Spigelian, lumbar, obturator)
• Abdominal wall masses (lipoma, desmoid tumour, endometrioma, abscess, haematoma)
• Abdominal wall reconstruction planning (component separation, mesh-based repair)
• Abdominal wall infection and necrotising fasciitis
• Diastasis recti
• Rare entities: abdominal wall metastases, primary malignancy

Diagnostic testing must answer three practical questions: What is the pathology?, Is there a complication (obstruction, strangulation, incarceration)?, and What is the surgical anatomy for planning repair?

Pathophysiology / Mechanism

Understanding the pathophysiological basis of abdominal wall failure informs which investigations are most informative:

• Hernia formation results from a mismatch between intra-abdominal pressure and the structural integrity of fascial layers - collagen cross-linking abnormalities, prior surgical devascularisation, and chronic elevation of intra-abdominal pressure all contribute
• Incisional hernias occur in 10-20% of laparotomies; risk is amplified by wound infection, obesity, malnutrition, steroid use, and suboptimal fascial closure technique
• Strangulation reflects venous outflow obstruction followed by arterial insufficiency in herniated contents - the femoral canal and narrow-necked indirect inguinal rings are particularly high-risk anatomic sites
• Diastasis recti is a midline fascial attenuation rather than a true hernia; the linea alba widens without a discrete defect ring, and symptoms arise from core instability rather than incarceration risk
• Abdominal wall masses may originate from any tissue layer (skin, subcutaneous fat, fascia, muscle, peritoneum) - distinguishing benign from malignant lesions and establishing the layer of origin drives management

Clinical Features / Diagnosis

History

A thorough history identifies features that refine the probability of specific diagnoses and flag urgency:

• Site and onset - epigastric versus groin versus flank; spontaneous versus post-operative
• Reducibility - a previously reducible lump that is no longer reducible represents acute incarceration until proven otherwise
• Associated symptoms - nausea, vomiting, and absolute constipation suggest bowel obstruction; fever and localised erythema suggest strangulation or infection
• Prior abdominal surgery - type of incision, wound complications, mesh history
• Risk factors for recurrence: obesity (BMI $>30\,\text{kg/m}^2$), smoking, diabetes, steroid use, connective tissue disorders
• Occupational and functional demands - relevant to repair strategy and timing

Physical Examination

Clinical examination remains the cornerstone of abdominal wall diagnosis and is expected to be performed systematically at consultant level:

• Position - supine and standing; Valsalva manoeuvre / cough impulse assessment
• Inspection - visible bulge, skin changes, previous scar location and quality, enterocutaneous fistula
• Palpation - define fascial defect edges (size in centimetres), reducibility, tenderness, overlying skin viability, cough impulse
• Groin hernias specifically - differentiate indirect (impulse via internal ring above mid-inguinal point) from direct (medial to inferior epigastric vessels, broad-based, rarely incarcerates) and femoral (below and lateral to pubic tubercle); assess both sides simultaneously
• Trans-illumination - distinguishes hydrocele from inguinal hernia in the groin
• Diastasis - assessed with the patient performing a head-lift from supine; the midline ridge and gutter width are clinically estimated

Investigation / Monitoring

When Is Investigation Required?

Not every hernia requires pre-operative imaging. Clinical diagnosis alone is sufficient for:

• Straightforward primary inguinal or umbilical hernia in a low-risk patient
• Clearly reducible, symptomatic hernia with unambiguous examination findings

Imaging and further investigation are indicated when:

• Diagnosis is uncertain (groin pain without obvious hernia; atypical mass)
• Complex or recurrent hernia requiring operative planning
• Suspicion of incarceration or strangulation
• Abdominal wall mass with malignancy cannot be excluded
• Pre-operative risk stratification for major reconstruction is required

Imaging

Ultrasound

• First-line for most abdominal wall and groin queries in the outpatient setting
• Operator-dependent but widely available, inexpensive, no radiation, real-time dynamic assessment
• Dynamic ultrasound - performed supine and standing with Valsalva; distinguishes hernia from lymph node, lipoma, undescended testis, hydrocele, or femoral vessel aneurysm
• Accurately demonstrates the hernia sac, contents (bowel loops, omentum), fascial defect width, and reducibility in real time
• Particularly valuable for occult inguinal hernia - sensitivity approaches 90% for clinically impalpable hernias
• Useful for characterising abdominal wall masses - lipoma (homogeneous echogenic), haematoma (complex echogenic, evolution over serial scans), abscess (fluid with internal echoes), endometrioma (heterogeneous hypoechoic)
• Limitations: cannot fully characterise large or complex incisional hernias; posterior abdominal wall and obturator hernias are poorly seen

Computed Tomography (CT)

CT of the abdomen and pelvis (with intravenous contrast where clinically appropriate) is the investigation of choice for:

CT-specific hernia measurements relevant to operative planning:

• Hernia width (W) - defect diameter in centimetres; European Hernia Society (EHS) classification uses $W1 < 4\,\text{cm}$, $W2\;4\text{-}10\,\text{cm}$, $W3 > 10\,\text{cm}$
• Loss of domain - ratio of hernia sac volume to total abdominal cavity volume; a ratio $>20\%$ predicts post-operative abdominal compartment syndrome risk and may necessitate pre-operative pneumoperitoneum
• Axial images identify whether the hernia is midline, paramedian, flank (subcostal, lateral, iliac), or pelvic

MRI

• Reserved for specific scenarios where soft tissue characterisation is superior to CT
• Desmoid tumours - MRI with gadolinium precisely defines relationship to fascial planes, neurovascular structures, and extent of infiltration critical for margin planning
• Abdominal wall endometrioma - characteristic signal on T1 fat-saturated sequences (hyperintense); confirms diagnosis non-invasively
• Occult groin hernia - MRI of the groin (dynamic MRI or pubic symphysis protocol) is the most sensitive investigation ($>95\%$) when ultrasound is negative and clinical suspicion persists; also evaluates athletic pubalgia / sports hernia (posterior inguinal wall deficiency without sac)
• Spigelian hernia - occasionally requires MRI to confirm when ultrasound is equivocal; sac tracks between internal oblique and external oblique aponeurosis along the semilunar line

Plain Radiography

• Rarely useful in isolation
• Erect chest X-ray and abdominal X-ray may confirm small bowel obstruction in the context of acute incarceration (dilated loops, air-fluid levels, absence of rectal gas)
• Identify free intraperitoneal gas if perforation complicates strangulation

Physiological and Laboratory Investigations

Blood Tests for Acute Presentations

Pre-operative Cardiorespiratory Assessment

Large incisional hernia repair - particularly with component separation and mesh reinforcement - carries substantial physiological burden. Pre-operative investigation should be proportionate to operative magnitude:

• Spirometry / Pulmonary function tests - essential before major abdominal wall reconstruction; reduced FEV₁ or FVC predicts post-operative respiratory failure, particularly when hernia contents are reduced back into a tight abdomen
• Echocardiography - for patients with functional impairment or known cardiac disease (assesses LV function and valvular disease before planned lengthy reconstruction)
• Cardiopulmonary exercise testing (CPET) - used selectively in high-risk patients; $\dot{V}O_2$ max $< 15\,\text{mL/kg/min}$ identifies patients at elevated perioperative risk who may benefit from prehabilitation or staged repair

Tissue Diagnosis

Fine Needle Aspiration Cytology (FNAC) and Core Biopsy

• Required when an abdominal wall mass cannot be characterised as benign by clinical and imaging features alone
• Core biopsy (14-18G) is preferred over FNAC for histological architecture and immunohistochemistry
• Essential for suspected desmoid tumour, soft tissue sarcoma, lymphoma, or metastatic deposit before definitive surgery - biopsy tract must be planned along the line of the proposed excision to allow en bloc resection if malignant
• CT-guided biopsy for deep or posterior wall lesions
• Ultrasound-guided biopsy for superficial masses

Seroma and Fluid Aspiration

• Diagnostic aspiration of a post-operative fluid collection guides management
• Send for: microscopy, culture and sensitivity, amylase (if pancreatic fistula is possible), cytology (if malignancy is suspected)
• Aspiration of mesh-associated seromas should be reserved for symptomatic cases - routine aspiration risks introducing infection

Hernia Classification Systems Relevant to Investigation

Understanding the classification frameworks helps contextualise which investigations generate the data points needed for classification:

Complications & Special Considerations

Strangulated Hernia - Investigation Does Not Delay Theatre

• Haemodynamically unstable or peritonitic patients with a strangulated hernia should proceed to emergency laparotomy; imaging is not required and must not delay operative source control
• CT is appropriate in the haemodynamically stable patient with diagnostic uncertainty (e.g., obturator hernia, Richter hernia with atypical presentation) - CT sensitivity for bowel ischaemia is approximately 83%, and it directs incision planning
• The Howship-Romberg sign (inner thigh pain radiating to knee on hip extension/internal rotation) suggests obturator hernia - CT confirms

Recurrent Hernia Investigation

• Always obtain operative notes from previous repair(s) - type of mesh, fixation technique, and anatomical approach inform both imaging interpretation and operative strategy
• CT with mesh protocol (thinner slices through the abdominal wall) demonstrates mesh position, bridging or folding, and the relationship of recurrent defect to mesh edges
• Consider assessing for underlying collagen disorder (Marfan syndrome, Ehlers-Danlos) in young patients with multiple recurrences - clinical genetics referral

Abdominal Wall Malignancy

• A history of prior intra-abdominal malignancy (colorectal, ovarian, urothelial) should raise suspicion for port-site metastasis or direct invasion in any new abdominal wall mass in the relevant post-operative period
• CT chest-abdomen-pelvis with contrast is the staging investigation of choice; PET-CT may add value for soft tissue sarcoma or when CT is inconclusive
• Primary abdominal wall sarcoma is rare; MRI defines local extent; biopsy must precede resection

Abdominal Wall Necrotising Fasciitis

• Fournier's gangrene and abdominal wall necrotising fasciitis are surgical emergencies - investigation must not delay debridement
• Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC) score incorporates: CRP, WBC, haemoglobin, sodium, creatinine, and glucose - a score $\geq 6$ raises suspicion; $\geq 8$ is highly predictive
• CT is the most sensitive imaging modality (identifies subcutaneous gas tracking along fascial planes, fascial thickening, fat stranding) and may demonstrate extent of involvement; sensitivity approximately 88-90%
• Clinical diagnosis overrides imaging - if the diagnosis is clinically apparent, take the patient to theatre immediately

Perioperative Management

Pre-operative Optimisation Guided by Investigation Results

• Loss of domain identified on CT: consider pre-operative progressive pneumoperitoneum (PPP) - weekly intraperitoneal insufflation to gradually expand the abdominal cavity over 2-4 weeks; reduces risk of abdominal compartment syndrome post-repair
• Pulmonary function impairment: pre-operative chest physiotherapy, smoking cessation (minimum 8 weeks), and respiratory prehabilitation
• Nutritional deficiency identified biochemically (albumin $< 30\,\text{g/L}$, pre-albumin $< 0.15\,\text{g/L}$): nutritional optimisation pre-operatively reduces mesh infection risk
• Occult DM: HbA1c $>8\%$ warrants endocrine optimisation before elective reconstruction
• Obesity: BMI $> 35\,\text{kg/m}^2$ significantly increases wound complication and mesh infection rate; weight loss to BMI $< 35\,\text{kg/m}^2$ before elective repair is recommended - bariatric surgery should be considered for BMI $> 40\,\text{kg/m}^2$ if repair is not urgent

Intraoperative Decision-Making Informed by Pre-operative Workup

• CT-derived defect width directly influences mesh selection (W1: onlay or sublay; W2-W3: component separation with retromuscular/preperitoneal mesh)
• Tissue biopsy results determine margin requirements for excision of abdominal wall masses (sarcoma: $\geq 1\,\text{cm}$ margins; desmoid: wide margins or observation depending on growth kinetics)
• Nutritional and cardiorespiratory investigations determine whether a staged approach (stoma relocation before hernia repair) is safer than a single-stage reconstruction

Summary: Diagnostic testing for abdominal wall disorders is driven by clinical context. Ultrasound is first-line for most groin and superficial abdominal wall pathology. CT is the definitive investigation for complex incisional hernias, acute incarceration, and pre-operative reconstruction planning. MRI excels in soft tissue characterisation (desmoid, endometrioma, occult groin hernia). Tissue biopsy must precede excision of any mass where malignancy is possible. Strangulation and necrotising fasciitis are operative emergencies - investigation does not take precedence over prompt surgical intervention.