Ultrasound in the Diagnosis and Management of Intra-Abdominal Sepsis

Principles of Ultrasound

• Reflection - at tissue interfaces; the basis of image generation
• Absorption - energy lost to tissue heating
• Scattering - from small structures, generating echoes in all directions
• Refraction - change of direction at interfaces; a source of artifacts
• Attenuation - overall reduction in signal intensity with depth, limiting penetration

• Axial (along the beam): determined by pulse frequency - higher frequency = better axial resolution
• Lateral (perpendicular to beam): determined by beam width
• Elevational (slice thickness): related to transducer aperture

Ultrasound in Diagnosis of Intra-Abdominal Sepsis

Clinical Context

Role of Ultrasound vs. CT

• Septations and loculations within abscesses are often better visualized with US than CT
• Subphrenic fluid - CT sometimes cannot distinguish subphrenic from pleural fluid, whereas US clarifies this with ease
• Hepatic abscesses - US can distinguish infected parenchyma, necrosis, and liquefaction; a hepatic abscess typically appears as a mixed hypoechoic and hyperechoic collection with irregular margins (Fischer's Mastery of Surgery, 8e)
• Pregnant patients - US is particularly valuable for suspected appendicitis/appendiceal abscess in pregnancy, where ionizing radiation is undesirable
• Bedside FAST (Focused Assessment with Sonography in Trauma/critical illness) - evaluates for free intraperitoneal fluid in patients with shock or peritonitis (Rosen's Emergency Medicine)
• Real-time guidance - uniquely suitable for procedural interventions (see below)

Ultrasound in Management of Intra-Abdominal Sepsis

1. Ultrasound-Guided Percutaneous Drainage

• Provides real-time visualization of needle and catheter advancement into the abscess
• Multiplanar capability is particularly useful for dome or cephalad abscesses, enabling oblique needle trajectories that avoid overlying structures
• Color Doppler identifies and allows avoidance of large blood vessels along the access route
• Position confirmation: normal saline can be instilled through the drain while Doppler detects the resulting flow signal, confirming catheter tip is within the abscess cavity (Fischer's Mastery of Surgery, 8e)

• Small abscesses (<3 cm): antibiotics alone; US-guided needle aspiration may assist diagnosis
• 3-4 cm: percutaneous needle aspiration (PNA) guided by US + antibiotics

• 5 cm or high-risk patients: percutaneous catheter drainage (PCD) under US or CT guidance

• CT is preferred when US is limited by deep location, bowel gas, or body habitus

2. Intraoperative Ultrasound

3. Monitoring and Follow-Up

Summary Table

Diagnosis of Tubercular Infection in General Surgical Patients

1. Clinical Assessment

• Constitutional symptoms: fever, night sweats, weight loss, anorexia
• Cough, hemoptysis (pulmonary component)
• Abdominal pain, distension, ascites, or a palpable mass (peritoneal/intestinal TB)
• History of exposure to a known TB case, residence in an endemic area, immunosuppression (HIV, steroid use, organ transplant), diabetes mellitus, malnutrition, or chronic renal failure

2. Tuberculin Skin Test (Mantoux / PPD Test)

• BCG vaccination can cause false-positive reactions (though PPD remains useful even in BCG-vaccinated individuals)
• Immunosuppressed patients (especially HIV with CD4 count <100 cells/μL) may have false-negative (anergic) results - PPD has near-zero sensitivity at this level
• A positive PPD in an asymptomatic patient with normal chest X-ray indicates latent infection, not active disease

3. Interferon-Gamma Release Assays (IGRAs)

• Require only a single blood draw (no return visit needed)
• Higher specificity for M. tuberculosis - less affected by BCG vaccination
• No anamnestic (boosting) effect on repeat testing
• More reproducible

• At CD4 counts <100 cells/μL, most results are indeterminate
• Cannot distinguish active from latent TB
• More costly; requires laboratory infrastructure

4. Microbiological Methods

a. Acid-Fast Bacilli (AFB) Smear Microscopy

• Sensitivity of sputum AFB smear: 29-67% (depends on specimen quality)
• Specificity: ~92% even in HIV patients
• At least two morning sputum specimens should be collected
• Gastric aspirates (3 consecutive mornings) useful in children and those unable to produce sputum - yield only ~50%
• Smear alone does not confirm M. tuberculosis (cannot distinguish from non-tuberculous mycobacteria)

b. Mycobacterial Culture

• Specimens: sputum, gastric aspirate, bronchial washing, pleural fluid, CSF, urine, pus, tissue biopsy
• LJ medium: results in 4-8 weeks
• Liquid BACTEC/MGIT system: early growth detected in 5-14 days
• Sensitivity approaches 100% in patients able to produce adequate sputum
• Culture is mandatory for drug susceptibility testing (DST), which guides treatment selection

5. Molecular / Nucleic Acid Amplification Tests (NAATs)

• Applicable to sputum, CSF, pleural fluid, gastric aspirate, ascitic fluid, urine, and tissue
• Smear-positive and culture-positive cases: sensitivity 95-98%, specificity very high
• Smear-negative, culture-positive cases: sensitivity falls to 57-78%
• Rapid results (hours vs. weeks for culture)
• The GeneXpert MTB/RIF (Xpert) assay simultaneously detects M. tuberculosis and rifampicin resistance within 2 hours
• PCR on CSF: 94% sensitivity and 100% specificity for culture-confirmed TB meningitis in one series
• PCR can also be used on early-growing culture isolates to detect drug resistance rapidly by identifying known genetic polymorphisms (e.g., rpoB mutations for rifampicin resistance)

6. Radiology

Chest X-Ray

• Upper lobe cavitary lesions are characteristic of reactivation TB
• Other findings: hilar/mediastinal lymphadenopathy, patchy infiltrates, apical scarring, pleural effusions, miliary pattern (millet-seed granulomas diffusely scattered - indicates disseminated disease)
• Primary TB: consolidation at the apex of a lower lobe or base of an upper lobe
• A normal chest X-ray does not exclude extrapulmonary TB

Abdominal Imaging (CT / Ultrasound / MRI)

• CT abdomen: mesenteric lymphadenopathy (often with central necrosis/low attenuation), peritoneal thickening, ascites, gut wall thickening, psoas abscess
• Ultrasound: free fluid, lymph nodes with central necrosis, gut wall thickening
• MRI: best delineates soft tissue extent, particularly in spinal TB (Pott's disease) and psoas abscess

7. Ascitic Fluid Analysis

• High protein concentration (exudative ascites)
• Adenosine deaminase (ADA) activity - elevated in tuberculous ascites; however, sensitivity is reduced in patients with cirrhosis
• Microscopy and culture of ascitic fluid for AFB
• Cytology to exclude malignancy

8. Histopathology and Tissue Biopsy

• Excision biopsy of lymph nodes - for cervical, mesenteric, or inguinal lymphadenopathy; tissue is sent for histopathology, AFB smear, culture, and PCR
• Peritoneal biopsy - if tuberculous peritonitis suspected and less invasive methods are inconclusive; laparoscopy allows direct visualization of the peritoneum (which typically shows multiple white miliary nodules or tubercles) and targeted biopsy
• Gut biopsy - via colonoscopy (ileocecal region most commonly affected) or operative biopsy
• Liver biopsy - for hepatic TB or miliary involvement
• Bone biopsy - in Pott's disease or other skeletal TB
• Fine Needle Aspiration Cytology (FNAC) - useful for superficial lymphadenopathy or cold abscesses; smear and culture from aspirate; less invasive than excision biopsy

9. Laparoscopy

• Direct visualization of peritoneal tubercles ("frosted glass" peritoneum or white miliary nodules)
• Guided peritoneal biopsy for histopathology and culture
• Assessment of intra-abdominal organs

10. Blood Tests and Adjuncts

• Full blood count: lymphocytosis, anaemia of chronic disease
• ESR and CRP: elevated but non-specific
• Serum ADA: may be elevated in disseminated TB
• Blood culture for mycobacteria: positive in 26-42% of HIV-positive TB patients; yield increases with lower CD4 counts
• HIV testing: mandatory in any TB suspect, as co-infection alters presentation, diagnostic sensitivity, and management

Summary: Diagnostic Approach in Surgical Patients

Radionuclide Imaging: Principles and Applications in General Surgery

PART 1: PRINCIPLES OF RADIONUCLIDE IMAGING

1.1 Basic Concept

1.2 Radioactive Decay and Emission

• Gamma (γ) rays - electromagnetic radiation detected by gamma cameras (used in planar scintigraphy, SPECT)
• Positrons (β⁺) - emitted by positron-emitting isotopes; each positron annihilates with a nearby electron to produce two 511 keV gamma photons traveling in opposite directions (used in PET)
• Beta (β⁻) particles - used for therapeutic applications (e.g., radioiodine ablation)

• Emits only gamma rays (no particulate radiation, which increases patient dose without contributing to imaging)
• Short physical half-life (minimizes radiation exposure)
• Energy of ~140 keV (optimal for gamma camera detection)
• Stable enough to allow preparation and administration

1.3 The Radiopharmaceutical

• Half-life of 6 hours (short enough to limit radiation dose, long enough for imaging)
• Gamma energy of 140 keV (ideal for gamma camera)
• Easily produced from a portable molybdenum-99/technetium-99m generator ("moly cow") in the nuclear medicine department
• Can be attached to many different carrier molecules

1.4 Image Acquisition Devices

Gamma Camera (Anger Camera)

• A lead collimator - allows only gamma rays travelling perpendicular to the detector to pass through, providing spatial information
• A sodium iodide (NaI) crystal - converts gamma photons into light flashes (scintillations)
• An array of photomultiplier tubes (PMTs) - convert scintillations into electrical signals
• Electronic circuitry - localizes each detected event to produce a 2D image

SPECT (Single Photon Emission Computed Tomography)

PET (Positron Emission Tomography)

1.5 Half-Life and Radiation Dosimetry

• Physical half-life (t½): time for the radionuclide to decay to half its radioactivity
• Biological half-life: time for the body to eliminate half the substance by normal biological processes
• Effective half-life: combination of both; determines patient radiation exposure
• Radiation dose is low (typically 1-10 mSv per procedure) and generally accepted as safe

1.6 Functional vs. Anatomical Imaging

PART 2: APPLICATIONS IN GENERAL SURGERY

2.1 Gastrointestinal Bleeding - Tagged Red Blood Cell (RBC) Scan

• The patient's erythrocytes are labelled with ⁹⁹ᵐTc in vitro and re-injected
• Dynamic gamma camera images are acquired over up to 4 hours
• Bleeding is detected as focal, progressive accumulation of radioactivity outside the normal vascular structures in a bowel segment, moving in the direction of peristalsis
• Minimum detectable bleeding rate: 0.05-0.2 mL/min - more sensitive than angiography (which requires 0.5-1.0 mL/min)
• Overall diagnostic positive rate ~45%, with ~78% accuracy in localising the true bleeding site
• Best suited for intermittent or obscure overt GI bleeding after inconclusive endoscopy/colonoscopy
• SPECT/CT provides more precise cross-sectional localisation to aid surgical planning when endoscopy has failed
• Limitation: active bleeding must be occurring at the time of imaging; rapid luminal transit of labelled blood can cause false-positive localisation to the colon when bleeding originates in the upper GI tract

2.2 Meckel's Diverticulum - Pertechnetate Scan

• Ectopic gastric mucosa secretes pertechnetate (as it does iodide), producing a "hot spot" in the right iliac fossa or lower abdomen
• Sensitivity ~85% in children, lower (~62%) in adults
• Pharmacological enhancement with pentagastrin (increases uptake) or H₂ blockers/cimetidine (reduces luminal secretion, improving contrast) can improve sensitivity
• Indications: unexplained lower GI bleeding in children/young adults, recurrent abdominal pain
• A positive scan is a strong indication for surgical resection

2.3 Hepatobiliary Imaging - HIDA Scan

• Acute cholecystitis: non-visualisation of the gallbladder (cystic duct obstruction) at 1 hour - sensitivity ~95%, specificity ~90%; morphine augmentation improves specificity
• Bile leak after cholecystectomy or hepatobiliary surgery: radioactivity accumulates outside the biliary tree; identifies the site and extent of the leak
• Biliary atresia in neonates: failure of excretion into the bowel
• Choledochal cyst delineation
• Post-operative biliary stricture assessment
• Gallbladder ejection fraction (GBEF): in chronic acalculous cholecystitis; GBEF <35% after cholecystokinin stimulation is diagnostic

2.4 Sentinel Lymph Node (SLN) Mapping - Lymphoscintigraphy

• Pre-operative lymphoscintigraphy - gamma camera imaging to map the lymphatic drainage pattern
• Intraoperative gamma probe (hand-held) - the surgeon uses the probe to detect radioactivity in the operative field and excise the "hot" node(s)
• Often combined with blue dye (patent blue/isosulfan blue) for dual localisation

• Breast cancer: SLN biopsy has replaced routine axillary lymph node dissection (ALND) in clinically node-negative patients; if SLN is negative, ALND is avoided, reducing morbidity (lymphoedema, nerve injury)
• Melanoma: SLN status is the most important prognostic factor in clinically stage I/II melanoma; lymphoscintigraphy is particularly valuable because melanoma can drain to unexpected lymph node basins (e.g., interval nodes, direct drainage to multiple basins)
• Other cancers: head and neck cancer, vulval cancer, penile cancer, and increasingly gastric and colorectal cancer in selected cases

2.5 Thyroid and Parathyroid Surgery

Thyroid Scintigraphy (¹²³I / ⁹⁹ᵐTc-pertechnetate)

• Assessment of thyroid nodules: "cold" nodules have higher malignancy risk; "hot" (autonomous) nodules are usually benign
• Localisation of ectopic thyroid tissue (lingual, substernal)
• Post-thyroidectomy whole-body ¹³¹I scan to detect residual thyroid tissue and distant metastases from differentiated thyroid cancer
• ¹³¹I is both diagnostic and therapeutic (ablation of residual thyroid/metastases)

Parathyroid Scintigraphy (⁹⁹ᵐTc-MIBI / Sestamibi)

• Pre-operative localisation of parathyroid adenomas in primary hyperparathyroidism
• Sestamibi is preferentially retained in hyperfunctioning parathyroid cells (due to their high mitochondrial content) while washing out from normal thyroid tissue
• Dual-phase MIBI scan (early at 15 min + delayed at 2-3 hrs) exploits differential washout
• SPECT/CT improves anatomical localisation, especially for ectopic adenomas (mediastinal, intrathyroidal)
• Enables focused/minimally invasive parathyroidectomy rather than bilateral neck exploration
• Sensitivity ~80-90% for solitary adenomas, lower for multiglandular disease

2.6 Tumour Staging and Detection

PET/CT with ¹⁸F-FDG

• Colorectal cancer: staging, detection of hepatic and extrahepatic metastases, discrimination of recurrent tumour from post-treatment fibrosis; PET/CT increasingly used for recurrent/metastatic disease
• Oesophageal and gastric cancer: staging, assessment of response to neoadjuvant chemoradiation
• Lymphoma staging: pre- and post-treatment assessment (superior to CT alone)
• Lung cancer: staging, characterisation of solitary pulmonary nodules
• Unknown primary tumour: whole-body FDG-PET can identify the primary in ~25-40% of cases
• Melanoma and breast cancer: distant metastasis detection

Octreotide Scan (¹¹¹In-Pentetreotide / ⁶⁸Ga-DOTATATE PET)

• Neuroendocrine tumours (NETs): carcinoid tumours, gastrinomas (Zollinger-Ellison syndrome), insulinomas (variable uptake), VIPomas, glucagonomas
• Somatostatin receptor scintigraphy (SRS) exploits overexpression of somatostatin receptors on NETs
• ⁶⁸Ga-DOTATATE PET/CT has largely superseded ¹¹¹In-Octreoscan due to superior sensitivity and resolution
• Essential for localising primary and metastatic NETs before surgery, and for selecting patients for peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE (theranostics)

2.7 Bone Scan (⁹⁹ᵐTc-MDP)

• ⁹⁹ᵐTc-methylene diphosphonate (MDP) accumulates in areas of increased osteoblastic activity
• Detection of skeletal metastases from breast, prostate, lung, and other cancers - more sensitive than plain radiography (detects ~30-40% bone destruction on X-ray vs. functional change on scan)
• Diagnosis of osteomyelitis, stress fractures, and Paget's disease
• Surgical relevance: guides extent of resection in limb salvage surgery; detects synchronous skeletal lesions before major resection

2.8 Infection and Inflammation

• ⁶⁷Ga-citrate scan / ¹¹¹In-labelled white cell (leukocyte) scan: localisation of occult abscesses, osteomyelitis, infected prostheses, and fever of unknown origin
• ¹¹¹In-WBC scan: the patient's leukocytes are labelled ex vivo and re-injected; they migrate to sites of infection/inflammation
• Useful when CT/MRI are inconclusive, particularly for post-operative collections and prosthetic joint/graft infection

2.9 Adrenal and Endocrine Surgery

• MIBG (¹²³I-metaiodobenzylguanidine) scan: localises phaeochromocytoma (primary and recurrent/metastatic) and neuroblastoma; ¹³¹I-MIBG can also be used therapeutically
• Adrenal cortex imaging (¹³¹I-cholesterol/NP-59 scan): distinguishes autonomous adrenal adenoma from bilateral hyperplasia in Conn's syndrome or Cushing's disease

Summary of Key Applications

The Role of Interventional Radiology in Surgical Diseases

Core IR Techniques

• Metallic coils / plugs - permanent; for selective arterial occlusion
• Gelatin sponge (Gelfoam) - temporary; recanalization expected; useful in trauma
• Polyvinyl alcohol (PVA) particles - permanent; for tumour devascularisation
• Liquid agents (glue, ethanol) - for arteriovenous malformations
• Drug-eluting beads (DEBs) - loaded with chemotherapy; for tumour treatment (Grainger & Allison)

APPLICATIONS IN GENERAL SURGERY

1. Gastrointestinal Haemorrhage

• CT angiography (MDCTA) - first-line investigation; detects active bleeding at rates ≥0.35 mL/min; identifies the source, guides selective catheterisation, and maps aberrant anatomy to reduce radiation and contrast during the procedure (Grainger & Allison)
• Catheter angiography detects bleeding at ≥0.5 mL/min; shows active contrast extravasation into the bowel lumen

• Upper GI bleeding (peptic ulcer, post-ERCP haemorrhage, Dieulafoy lesion, post-operative bleeding): superselective embolisation of the left gastric, gastroduodenal, or superior mesenteric artery branches
• Lower GI bleeding (diverticular disease, angiodysplasia): precise identification of the bleeding branch required to avoid ischaemia; prophylactic embolisation feasible even without active extravasation if the site is known
• Alternative: intra-arterial vasopressin infusion to cause vasoconstriction
• If surgery is required, an angiographic catheter can be left in situ to guide intraoperative identification of the bleeding site (Schwartz's Principles of Surgery, 11e)

2. Solid Organ Trauma (Liver, Spleen, Kidney)

• Splenic injury: Angioembolisation (using gelatin sponge or coils) of injured splenic vessels arrests haemorrhage without splenectomy, preserving splenic immune function. Proximal splenic artery embolisation reduces perfusion pressure while preserving flow via collaterals
• Renal injury: Superselective embolisation of bleeding renal vessels avoids nephrectomy
• Hepatic injury: Embolisation of injured hepatic arterial branches; particularly useful for grade III-V injuries
• Pelvic fractures with haemorrhage: Selective embolisation of internal iliac artery branches; temporary gelatin sponge occlusion is favoured as recanalization is desirable once the vessel heals
• Extremity vascular trauma: Balloon occlusion for haemorrhage control; stent grafts to restore arterial continuity (Bailey & Love's Short Practice of Surgery, 28e; Grainger & Allison)

3. Vascular Surgery Applications

Peripheral Arterial Disease (PAD)

• Iliac artery stenosis/occlusion: PTA alone or with stenting; technical success ~100% for stenoses; ~80% for occlusions. Five-year patency 64-75% - comparable to surgery for iliac disease with far less morbidity (Grainger & Allison)
• Femoropopliteal disease: PTA; drug-coated balloons and stents improve durability
• Infrapopliteal disease: Angioplasty for critical limb ischaemia (CLI); used as part of limb salvage strategy

Abdominal Aortic Aneurysm (AAA) - EVAR

• Indications: AAA ≥5.5 cm in diameter (men), ≥5.0 cm (women), or rapidly expanding
• Advantages over open repair: lower 30-day mortality, reduced blood loss, shorter hospital stay
• Complications: endoleak (persistent sac perfusion - most important long-term issue), stent migration, graft limb thrombosis - all requiring long-term surveillance with CT angiography
• TEVAR (Thoracic Endovascular Aortic Repair) for thoracic aortic aneurysms and aortic dissection

Carotid Artery Stenosis

• Carotid artery stenting (CAS) is an alternative to surgical endarterectomy for symptomatic stenosis (70-99%)
• Cerebral protection devices are deployed to prevent distal embolism during the procedure
• Evidence suggests stenting has higher minor stroke rates (especially in the elderly); endarterectomy has more myocardial infarctions; decision requires multidisciplinary input (Grainger & Allison)

Venous Thromboembolism

• Catheter-directed thrombolysis (CDT) for extensive iliofemoral DVT - reduces risk of post-thrombotic syndrome (PTS)
• Inferior vena cava (IVC) filter insertion - in patients with proximal DVT/PE who cannot receive anticoagulation (e.g., preoperative patients, contraindications); retrievable filters are preferred
• Pulmonary embolism: Catheter-directed thrombolysis or mechanical thrombectomy for massive PE with haemodynamic compromise

4. Hepatobiliary and Pancreatic Surgery

Biliary Drainage and Stenting

• Percutaneous Transhepatic Cholangiography and Drainage (PTCD/PTBD): used when ERCP has failed or is inaccessible
  • Malignant biliary obstruction (pancreatic head cancer, cholangiocarcinoma, gallbladder cancer): self-expanding metal stents (SEMS) placed across the stricture; provides palliation and improves liver function before surgery ("bridging")
  • Post-operative biliary stricture and bile leak
  • Biliary sepsis/cholangitis: urgent biliary decompression

Portal Hypertension - TIPS

• Indications: refractory variceal haemorrhage, refractory ascites, hepatic hydrothorax, Budd-Chiari syndrome
• Reduces portal pressure; reduces risk of rebleeding
• Complications: hepatic encephalopathy (shunting blood past the liver), stent stenosis/occlusion (Yamada's Textbook of Gastroenterology, 7e)

Tumour Ablation and Embolisation

• Transarterial Chemoembolisation (TACE): selective intra-arterial injection of chemotherapeutic agents (doxorubicin, cisplatin) combined with embolic material into the hepatic artery supplying a hepatocellular carcinoma (HCC) or colorectal metastases; exploits the dual blood supply of the liver (normal hepatocytes supplied by portal vein; tumours predominantly by hepatic artery). Drug-eluting bead TACE (DEB-TACE) provides sustained drug release
• Transarterial radioembolisation (TARE/SIRT): intra-arterial injection of yttrium-90 (⁹⁰Y) microspheres; delivers internal radiation selectively to liver tumours
• Radiofrequency Ablation (RFA) / Microwave Ablation (MWA): percutaneous probe insertion into liver, lung, or renal tumours; thermal energy destroys tumour with a margin of normal tissue; indicated for HCC, colorectal liver metastases, and renal cell carcinoma
• Cryoablation: percutaneous freeze-thaw cycles to destroy tumours (Fischer's Mastery of Surgery, 8e)

5. Abscess and Fluid Collection Drainage

• Percutaneous image-guided drainage (US or CT-guided) of intra-abdominal, pelvic, subphrenic, and retroperitoneal abscesses provides definitive treatment for 70-90% of abdominal abscesses
• Used for: post-operative collections, anastomotic leaks, Crohn's-related abscesses, diverticular abscesses, perforated appendicitis
• Step-up approach for necrotising pancreatitis: percutaneous/endoscopic drainage before surgical debridement
• Can serve as a "bridge to surgery" - controlling sepsis to allow resuscitation and planned definitive operation in a fitter patient (Grainger & Allison; Maingot's Abdominal Operations)

6. Urological Surgical Diseases

• Percutaneous nephrolithotomy (PCNL): IR-guided access to the collecting system for large or complex renal calculi
• Nephrostomy: temporary renal drainage in ureteric obstruction (malignancy, stone, stricture)
• Ureteric stenting (JJ stents): retrograde via cystoscopy or antegrade via nephrostomy for ureteric obstruction
• Renal artery angioplasty/stenting: for renovascular hypertension secondary to renal artery stenosis
• Varicocele embolisation: superselective embolisation of the spermatic vein for male infertility

7. Oncological / Staging Applications

• Image-guided biopsy for tissue diagnosis of abdominal masses, retroperitoneal nodes, liver lesions, lung nodules, and bone lesions - avoids open surgical biopsy in most cases
• Staging of cancer: CT-guided biopsy of suspected metastases to guide operative planning
• Port/central venous catheter insertion: IR-guided tunnelled catheter or port-a-cath placement for chemotherapy administration

8. Other Surgical Applications

• Aortic balloon occlusion (REBOA): resuscitative endovascular balloon occlusion of the aorta for haemorrhage control in damage control scenarios
• Embolisation before surgery (pre-operative devascularisation): reduces intraoperative blood loss for hypervascular tumours (e.g., large renal cell carcinoma, hypervascular bone metastases, paragangliomas)
• Oesophageal/colonic stenting: self-expanding metal stents for malignant obstruction - as palliation or bridge to elective surgery ("decompression before anastomosis")
• Gastrostomy/jejunostomy insertion: percutaneous radiological gastrostomy (PRG) and jejunostomy for nutritional support in surgical patients

Summary

Role of Colour Doppler in Vascular Surgery

Principles of Colour Doppler Ultrasound

1. B-mode (brightness mode) grey-scale imaging - provides real-time anatomical images of vessel walls, luminal diameter, and plaque morphology
2. Spectral (pulsed-wave) Doppler - measures blood flow velocity at a selected point and displays it as a waveform over time; yields quantitative data (peak systolic velocity [PSV], end-diastolic velocity [EDV], velocity ratios, resistance index)
3. Colour flow Doppler (CFD) - assigns colour (conventionally red = flow toward the transducer; blue = away) to each pixel based on mean Doppler frequency shift, providing a real-time map of flow direction and relative velocity across a vessel cross-section

• Aliasing - apparent colour reversal (mosaic pattern) when velocities exceed the Nyquist limit; indicates high-velocity flow through a stenosis
• Turbulence / spectral broadening - post-stenotic turbulent flow fills in the normally clear "window" beneath the systolic peak
• Colour void - absence of colour signal indicating occlusion or very low flow
• Waveform shapes: triphasic (normal peripheral artery - forward systolic, brief reverse diastolic, forward diastolic); biphasic (mild PAD); monophasic (severe proximal stenosis/occlusion - dampened, tardus-parvus waveform)

CLINICAL APPLICATIONS IN VASCULAR SURGERY

1. Carotid Artery Disease

• Normal internal carotid artery (ICA): low-resistance waveform with broad systolic peak and high diastolic flow (supplies the low-resistance cerebral circulation)
• Normal external carotid artery (ECA): high-resistance waveform with sharp systolic peak and minimal diastolic flow
• Normal common carotid artery (CCA): resembles ICA (80% of flow goes to ICA)

• At the site of stenosis: PSV increases, EDV increases further with increasing severity
• Colour aliasing (mosaic) at the stenosis; post-stenotic turbulence and spectral broadening distally
• Severe stenosis or occlusion → ipsilateral CCA shows high-resistance waveform (ECA-like pattern) due to increased downstream resistance
• Contralateral ICA PSV may be falsely elevated due to compensatory increased flow
• Grey-scale imaging characterises plaque as echogenic (calcified, more stable), echolucent (lipid-rich, vulnerable), heterogeneous, or ulcerated

• Pre-operative evaluation before carotid endarterectomy (CEA) - select patients with symptomatic ≥50% or asymptomatic ≥60-70% stenosis
• Post-operative surveillance after CEA for restenosis
• Post-stenting surveillance (ICA PSV >120-130 cm/s suggests in-stent restenosis)
• Screening in high-risk patients (TIA, stroke, peripheral arterial disease)

2. Peripheral Arterial Disease (PAD) of the Lower Limbs

• Triphasic: normal; forward systolic, brief reverse diastolic (reflecting arterial wall compliance), forward diastolic
• Biphasic: loss of reverse component; indicates proximal stenosis reducing arterial compliance
• Monophasic (tardus-parvus): slow-rising, low-amplitude, blunted waveform; indicates significant proximal occlusive disease

• Diagnosis and localisation of stenoses/occlusions: PSV doubling ratio >2:1 between stenotic and pre-stenotic segment indicates ≥50% diameter stenosis; >4:1 indicates ≥75% stenosis
• Pre-operative planning: mapping of disease extent (aortoiliac, femoropopliteal, infrapopliteal); identifying suitable inflow and outflow vessels for bypass
• Vein graft surveillance: post-bypass duplex identifies impending graft failure (PSV >300 cm/s or PSV ratio >3.5 at a stenosis; or very low PSV <45 cm/s throughout, indicating impending thrombosis) - allows timely intervention before graft occlusion
• EVAR surveillance: post-endovascular aneurysm repair monitoring for endoleak (colour flow within the excluded aneurysm sac) and graft limb stenosis/thrombosis
• Angioplasty/stent assessment: immediate post-procedure and follow-up
• Assessment of critical limb ischaemia (CLI): toe pressures, toe-brachial index

3. Abdominal Aortic Aneurysm (AAA)

• Screening: B-mode ultrasound remains the gold standard for AAA screening (maximum anteroposterior diameter ≥3 cm = aneurysm; ≥5.5 cm in men = threshold for repair)
• Colour Doppler: identifies slow, swirling flow within the aneurysm sac; detects mural thrombus (colour void in areas of thrombus); identifies neck and iliac involvement
• Post-EVAR surveillance: colour Doppler identifies:
  • Type I endoleak (perigraft flow at proximal/distal attachment zones)
  • Type II endoleak (retrograde flow from lumbar or inferior mesenteric artery into the sac - seen as colour signal within the excluded sac)
  • Graft limb occlusion (absence of colour flow in a graft limb)
  • Sac size change on serial B-mode measurements

4. Deep Vein Thrombosis (DVT)

• Acute thrombus - typically hypoechoic (soft, poorly echogenic) with a distended vein
• Chronic thrombus - hyperechoic, retracted, partially recanalised with irregular colour flow

• Proximal DVT (iliac, femoral, popliteal): standard protocol; sensitivity highest
• Calf vein DVT: requires whole-leg scan; clinical significance debated
• Upper limb DVT: subclavian/axillary vein evaluation - important in Paget-Schroetter syndrome (effort thrombosis)
• Colour Doppler differentiates DVT from Baker's cyst, cellulitis, and haematoma - avoiding unnecessary anticoagulation

• Confirm DVT before catheter-directed thrombolysis (CDT) for iliofemoral DVT
• Post-thrombotic surveillance for recanalization and reflux
• Pre-operative DVT screening before major elective surgery

5. Venous Insufficiency and Varicose Veins

• Great saphenous vein (GSV) and small saphenous vein (SSV): identifies saphenofemoral junction (SFJ) and saphenopopliteal junction (SPJ) incompetence
• Reflux: detected by reversed colour signal (blue on a red background or vice versa) lasting >0.5 seconds after calf squeeze release (standing patient with Valsalva provocation)
• Incompetent perforator veins: outward flow during calf squeeze identifies incompetent perforators
• Vein diameter mapping: guides choice of procedure (endovenous laser ablation [EVLA], radiofrequency ablation [RFA], or surgery)
• Pre-operative vein mapping for bypass conduit: assessment of GSV diameter, continuity, and patency before use as bypass graft

• Duplex-guided marking of the SFJ, SSV-SPJ, and incompetent tributaries in the pre-operative bay
• Identifies anatomical variations (duplicated GSV, high SPJ entry) that alter operative approach
• Post-operative surveillance for recurrent reflux and recanalization after endovenous procedures

6. Renal Artery Stenosis (RAS)

• PSV >180-200 cm/s in the renal artery
• Renal artery to aortic PSV ratio (RAR) >3.5 indicates haemodynamically significant stenosis (>60% stenosis)
• Colour aliasing at the stenosis

• Tardus-parvus waveform - slow rise (prolonged acceleration time >70-100 ms), reduced amplitude, blunted systolic peak - in the segmental/interlobar arteries distal to a haemodynamically significant RAS
• Reduced resistive index (RI = [PSV-EDV]/PSV) in the affected kidney

• Screening for RAS in resistant/refractory hypertension
• Post-renal artery angioplasty/stenting surveillance

7. Visceral Arterial Disease

• Coeliac axis and superior mesenteric artery (SMA) stenosis/occlusion: PSV >200 cm/s in the SMA or >275 cm/s in the coeliac axis (fasting) suggests haemodynamically significant stenosis
• Used to diagnose chronic mesenteric ischaemia and plan visceral revascularisation
• Median arcuate ligament syndrome: compression of coeliac axis detected on deep expiration with colour flow attenuation

8. Intraoperative and Procedural Uses

• Intraoperative duplex after CEA: immediate assessment of endarterectomy result; detects residual intimal flap, stenosis, or thrombosis before wound closure - avoiding early reoperation
• Intraoperative bypass graft assessment: confirms graft patency and flow post-anastomosis
• Duplex-guided vascular access: US-guided cannulation of femoral, brachial, and subclavian vessels for endovascular procedures reduces complication rates
• Pseudo-aneurysm compression and thrombin injection: colour Doppler identifies iatrogenic femoral artery pseudo-aneurysms and guides US-guided thrombin injection for treatment

9. Venous Access and Haemodialysis

• Pre-operative vein mapping for arteriovenous (AV) fistula creation in end-stage renal disease: assesses cephalic/basilic vein diameter (≥2.5 mm required for AV fistula), flow, and continuity
• AV fistula surveillance: colour Doppler detects stenosis within the fistula or outflow vein (PSV >400 cm/s, ratio >2:1); guides timely balloon angioplasty to prevent fistula failure
• Central venous catheter insertion: US guidance reduces pneumothorax, arterial puncture, and haematoma risks

Advantages of Colour Doppler in Vascular Surgery

Limitations

• Operator-dependent: significant skill required for accurate velocity measurements
• Bowel gas / obesity / calcification: impairs visualisation, especially for mesenteric and renal vessels
• Angle dependence: inaccurate measurements if insonation angle >60°
• Limited depth penetration for deep or obese patients
• Cannot fully replace CT angiography for pre-operative planning in complex aortic or multi-level disease
• Does not visualise intracranial vessels or the proximal aorta well