Diagnostic Techniques in Surgery

Overview

1. Plain X-ray (radiography)
2. Ultrasound (US)
3. Computed Tomography (CT)
4. Magnetic Resonance Imaging (MRI)
5. Biopsy (tissue diagnosis)

1. Computed Tomography (CT Scan)

Principle

Surgical Indications

Advantages

• Fast (seconds for whole-body scan)
• Widely available, 24/7 in emergency settings
• Excellent bone and vascular detail
• Guides interventional drainage (CT-guided drainage of abscesses)
• 3D reconstructions aid complex fracture planning

Contraindications

2. Magnetic Resonance Imaging (MRI)

Principle

Surgical Indications

Advantages

• No ionizing radiation - safe in young patients and for repeated scans
• Superior soft tissue contrast compared to CT
• Multiplanar imaging without repositioning
• Does not require iodinated contrast (gadolinium used instead)

Contraindications

3. Biopsy

Principle

Types of Biopsy

Key Principles (from Pye's Surgical Handicraft)

• For suspected carcinoma on sigmoidoscopy: biopsy should be taken from the edge of the lesion using large cusp forceps
• A partial biopsy of a polyp should be avoided because:
  1. The pathologist may have insufficient material to assess invasion through the muscularis mucosae (the criterion of malignancy)
  2. It may subsequently be difficult to locate the lesion for complete removal
• Polyps should therefore be removed by complete excision biopsy
• After biopsy: the site must be inspected for bleeding
• A barium enema should not be performed within 10 days of a biopsy owing to the risk of perforation

Indications for Biopsy

1. Suspected malignancy - to confirm diagnosis before treatment
2. Characterization of inflammatory/granulomatous disease (TB, sarcoidosis, Crohn's)
3. Lymphadenopathy of unknown cause
4. Suspicious breast lump, thyroid nodule, or skin lesion
5. Renal or hepatic parenchymal disease (interstitial nephritis, cirrhosis staging)
6. Monitoring treatment response in known malignancy
7. Suspected soft tissue sarcoma - mandatory before definitive surgery
8. Bone tumors - core or incisional biopsy before limb-salvage surgery

Contraindications to Biopsy

• Uncooperative patient (no safe positioning possible)
• Suspicion of a vascular lesion / AV malformation without vascular imaging
• Suspected hydatid cyst (risk of anaphylaxis from cyst fluid spillage)
• No consent

• Anticoagulant therapy or clotting disorders - risk of uncontrolled bleeding (as specifically noted in Pye's Surgical Handicraft: "a biopsy is contraindicated in patients on anticoagulants or with clotting disorders")
• Thrombocytopenia (platelets <50,000/mm3 for core biopsy)
• Overlying infection at the biopsy site (risk of seeding)
• Renal biopsy: solitary kidney (relative), uncontrolled hypertension, hydronephrosis
• Inaccessible site where procedure risk exceeds diagnostic benefit
• Suspected melanoma: incision biopsy is contraindicated (excision biopsy only, to avoid lymphatic dissemination)

4. Comparison Summary Table

5. Clinical Decision Framework

• Emergency (trauma / acute abdomen): CT is first-line when patient is stable; proceed directly to surgery if obvious diffuse peritonitis exists.
• Tumor staging/characterization: CT for initial staging; MRI for local staging (rectal cancer, liver lesions, sarcoma).
• Definitive tissue diagnosis: Biopsy is mandatory before chemoradiotherapy or major oncological resection.
• Pregnant patient: Avoid CT if possible; ultrasound or MRI preferred.
• Renal failure: Avoid iodinated CT contrast; MRI with gadolinium also risky below eGFR 15; use non-contrast modalities or US.

X-Ray (Plain Radiography) as a Diagnostic Technique in Surgery

Principle

• PA (postero-anterior) - chest
• AP (antero-posterior) - abdomen, trauma
• Lateral - spine, chest, foreign bodies
• Erect - chest and abdomen to detect free gas and fluid levels
• Supine - abdomen (AXR)

Standard Views and Their Surgical Uses

1. Erect Chest X-ray (CXR)

• Allow ~10 minutes after sitting the patient upright before taking the film so air can rise
• Seek free air under the right hemidiaphragm (to avoid confusion with left-sided gastric air bubble)
• Recognize Chilaiditi's syndrome - harmless asymptomatic interposition of large bowel between liver and diaphragm - as a mimic
• Postoperative free air can persist for up to 5-7 days - interpret with caution
• If CXR is equivocal or walled-off perforation is suspected, CT is the next step

2. Plain Abdominal Radiograph (AXR)

Surgical Indications for X-ray

A. Acute Abdomen

B. Trauma

• CXR in trauma: detect pneumothorax, haemothorax, rib fractures, widened mediastinum (aortic injury), diaphragmatic hernia
• Pelvic X-ray: pelvic ring disruption, acetabular fractures
• Limb X-rays: fractures, dislocations, foreign bodies
• Cervical spine X-ray: C-spine injury in trauma (now largely replaced by CT)

C. Orthopaedics

• Initial assessment of all suspected fractures
• Two views at 90° to each other are mandatory (AP + lateral) - a fracture visible only in one plane will be missed on a single view
• Two joints should be included for long-bone fractures (to exclude associated dislocation)
• Comparison views of opposite limb in children (to differentiate growth plates from fractures)
• Post-reduction and post-fixation assessment
• Monitoring of fracture healing - callus formation, union

D. Chest (General Surgery & Preoperative)

• Preoperative assessment for cardiorespiratory disease
• Lung cancer screening (though CT low-dose is now preferred)
• Pleural effusion, pulmonary collapse, pneumonia
• Mediastinal shift, widening
• Diaphragmatic hernia: bowel loops visible in chest

E. Urology

• KUB (Kidney-Ureter-Bladder) film: detect radio-opaque renal/ureteric calculi (80-90% of stones are radio-opaque)
• Bladder calculi
• Note: uric acid stones are radiolucent - missed on plain X-ray, require CT/IVU

F. Vascular Surgery

• Calcified aortic aneurysm outline on AXR (eggshell calcification)
• Foreign bodies/embolized stents

G. Swallowed/Inhaled Foreign Bodies

• CXR for inhaled foreign bodies
• Neck + chest X-ray for oesophageal foreign bodies
• Abdominal series to track ingested objects through GI tract

Special X-ray Techniques in Surgery

Contraindications

Absolute

• None that are absolute in a true emergency (life-saving benefit outweighs risk)

Relative / Important Considerations

• CXR = 0.1 mSv (equivalent to ~10 days natural background radiation)
• AXR = 0.7 mSv
• CT abdomen = 8-10 mSv (much higher - a major reason to prefer X-ray for initial assessment)

Limitations of Plain X-ray in Surgery

1. Low sensitivity for early/subtle findings - e.g., a normal AXR does not exclude SBO if loops are fluid-filled
2. Limited soft tissue contrast - CT and MRI are far superior for organ detail
3. No vascular information without contrast
4. 2D image - overlapping structures cause confusion; CT provides true cross-sectional anatomy
5. Operator/viewer dependent - requires experienced interpretation
6. Ionizing radiation - cumulative exposure is a concern

Summary

• Erect CXR for free gas in perforation
• AXR for bowel obstruction
• Bone X-rays for fractures
• KUB for radio-opaque urinary stones
• Preoperative CXR for cardiopulmonary assessment