Popliteal Artery Aneurysm (PAA)

Definition and Epidemiology

• Overwhelmingly affects men in their seventh decade of life
• ~50% are bilateral - the contralateral limb must always be examined
• 30-40% are associated with abdominal aortic aneurysm (AAA) - bilateral PAAs increase this risk further
• Up to 75% of PAA patients have aortic ectasia or aneurysm (Sabiston)
• Most are fusiform, true degenerative aneurysms associated with smoking, age, and hypertension

Clinical rule: Every patient diagnosed with a PAA requires ultrasound interrogation of the contralateral popliteal artery and the abdominal aorta. Conversely, all AAA patients should be screened for PAA.

Anatomy

• P1: adductor hiatus to the superior border of the patella
• P2: superior border of the patella to the center of knee articulation
• P3: knee articulation to the origin of the anterior tibial artery

Natural History

• Rupture is rare in true PAAs; any rupture should raise suspicion of a false/mycotic aneurysm
• ~1/3 of PAAs will thrombose within 5 years of diagnosis
• The mechanism: mural thrombus within the aneurysm sac embolizes to distal run-off vessels over time; as successive run-off vessels occlude, flow in the sac diminishes and eventually the aneurysm thromboses acutely
• By the time acute thrombosis occurs, the outflow vessels are chronically diseased, making reconstruction difficult and the limb loss rate as high as 50%
• Risk factors for progression: larger index size at presentation, presence of intramural thrombus, concurrent AAA

Clinical Presentation

Differential Diagnosis

1. Popliteal artery aneurysm - pulsatile, bruit on auscultation
2. Baker's (popliteal) cyst - synovial outpouching from the posteromedial knee between the medial gastrocnemius head and semimembranosus tendon, non-pulsatile
3. Arterial adventitial cyst - uncommon cystic structure from the artery wall
4. Benign or malignant tumor

Investigation

• Vein mapping (to assess ipsilateral and contralateral great saphenous vein)
• Baseline ankle-brachial index (ABI)
• Lower extremity CTA/MRA/conventional arteriogram

Indications for Repair

Treatment

Open Surgical Repair (Gold Standard)

1. Single-segment great saphenous vein (GSV) ≥3 mm diameter - ideal
2. Short saphenous or cephalic vein
3. Expanded PTFE or allograft (no-conduit cases)

• Patient supine, knee flexed and externally rotated
• Preferred for aneurysms extending beyond the popliteal fossa
• Proximal and distal incisions, tunnel created, bypass performed with saphenous vein or prosthetic graft
• The PAA must be ligated both proximally and distally as close as possible to the sac (failure to isolate may cause sac expansion and late rupture from patent geniculate collaterals)

• Patient prone
• Advantageous for large aneurysms confined to the popliteal space, allows aneurysmectomy and direct ligation of geniculate branches
• Limits exposure of superficial femoral and crural arteries - only use when aneurysm is confined to the popliteal fossa
• Short saphenous vein can be harvested in the prone position

Endovascular Repair

• Proximal and distal landing zones ≥15 mm in healthy vessel
• Minimal aneurysmal kinking or tortuosity
• Good tibiopedal runoff (≥2 patent vessels)
• Stent grafts oversized 10-15%; if multiple stents required, 2 cm overlap recommended
• Angiography with the knee flexed is performed to confirm stent sizing and avoid termination at the point of maximum flexure

• Aneurysms not crossing the knee (proximal popliteal / distal SFA)
• Patients of advanced age with significant medical comorbidities
• Patients who are NOT expected to survive ≥5 years (guidelines favor open for those with ≥5-year life expectancy)

Acute Presentation (Thrombosed PAA with Limb Ischemia)

1. Initiate anticoagulation immediately
2. CTA or conventional angiography - assess aneurysm thrombosis, extent of distal embolization, tibiopedal runoff
3. If motor/sensory function intact (mild ischemia): catheter-directed thrombolysis to restore runoff, followed by definitive repair
4. If profound/limb-threatening ischemia: immediate OR - thromboembolectomy of popliteal and tibial vessels (± pharmacomechanical thrombolysis), aneurysm exclusion, and bypass
5. If compartment syndrome suspected or confirmed: 4-compartment fasciotomy
6. Non-viable limb: primary amputation rather than futile revascularization

Postoperative Surveillance and Medical Therapy

• Duplex ultrasound at 3, 6, and 12 months during the first year, then annually
• Monitor for: graft patency, excluded sac size, flow
• Aspirin 81 mg indefinitely as minimum antiplatelet therapy
• Dual antiplatelet or anticoagulation: individualized risk-benefit assessment
• Standard cardiovascular risk-reduction: statins, antiplatelet agents, angiotensin blockade as indicated

Key Points Summary

Reactive Inguinal Lymph Node - Ultrasound

Key USG Features of a Reactive Lymph Node

B-Mode Ultrasound - Reactive Node Anatomy

1. Oval/reniform shape - the long axis is at least twice the short axis
2. Hypoechoic cortex - the peripheral lymphoid tissue appears dark (hypoechoic) relative to adjacent muscle
3. Echogenic (hyperechoic) central hilum - bright central stripe representing fatty/fibrovascular hilum; present in up to 92% of benign nodes
4. Concentrically thickened cortex - reactive cortex thickens uniformly (symmetrically) around the hilum due to immune/inflammatory response
5. Well-defined, smooth border
6. No necrosis, calcification, or extracapsular infiltration

Doppler Ultrasound Features

• Hilar vascularity - blood vessels enter and branch radially from the hilum (the "hilar flow" pattern)
• Flow is central, orderly, and low-impedance
• May show increased hilar vascularity compared to a resting node (due to active immune response)
• No peripheral cortical flow - this is the key reassuring feature
• ~96% of reactive nodes demonstrate hilar flow only

USG Images

• LN1 (Benign) - Normal flat oval node, barely visible, preserved hilum
• LN2 (Probably benign/Reactive) - Oval, visible nodal-core sign, concentrically thickened hypoechoic cortex due to immune response
• LN3 (Suspicious) - Round to oval, cortex thickened, hilum may be absent
• LN4 (Probably malignant) - Rounded, inhomogeneous, markedly thickened cortex
• LN5 (Malignant) - Large, rounded, heterogeneous, no hilum

Size Criteria

• Inguinal lymph nodes up to 1.5 cm in short axis are generally considered within normal limits
• Reactive nodes may enlarge but typically do not exceed 2-3 cm and retain oval shape
• Nodes with short axis ≥1 cm (oval-shaped) or ≥0.8 cm (circular-shaped) with a malignant morphology are considered suspicious
• Size alone is unreliable - morphology and Doppler pattern are more specific

Important Differential Points

Clinical Tip

• Lower limb infections (cellulitis, wound infections, tinea pedis)
• STIs (herpes simplex, syphilis, chancroid, LGV)
• Recent vaccinations (ipsilateral lower extremity or hip)
• Inflammatory skin conditions (eczema, psoriasis)
• Post-surgical drainage from perineum, gluteal region, lower abdomen

Inguinal Hernia - Ultrasound (USG)

Why Use Ultrasound?

• No radiation
• Real-time dynamic assessment (Valsalva, standing position)
• Portable and immediately available
• Can visualize hernia contents (fat vs. bowel vs. fluid)
• Can assess reducibility and detect complications (incarceration, strangulation)
• Sensitivity 86%, specificity 77% (meta-analysis, Schwartz Surgery)

Relevant Anatomy on USG

• Indirect hernia - protrudes lateral to the IEA through the deep inguinal ring, travels within the inguinal canal alongside the spermatic cord
• Direct hernia - protrudes medial to the IEA through Hesselbach's triangle (weakness in transversalis fascia)

Probe Technique

• Use a high-frequency linear probe (7.5-12 MHz) for thin patients; curved probe for obese patients
• Scan in long-axis (longitudinal) and short-axis (transverse) planes along the inguinal canal
• Always perform with the patient:
  1. Supine at rest (baseline)
  2. Valsalva maneuver or coughing (to increase intra-abdominal pressure and elicit herniation)
  3. Standing if no hernia seen supine (increases sensitivity significantly)
• Movement (sliding) of abdominal contents through the canal during Valsalva is essential for diagnosis

Ultrasound Appearance of Hernia Contents

USG Images

1. Anatomy Overview - Bowel-Containing Inguinal Hernia

2. Direct vs. Indirect Hernia - Relationship to the Spermatic Cord

• Indirect hernia sac lies anterior to the spermatic cord - it travels with the cord through the deep ring
• Direct hernia sac lies posterior to the spermatic cord - it pushes the cord anteriorly and laterally

3. Dynamic Assessment - Indirect Hernia Containing Fat

4. Right Inguinal Hernia - B-Mode Scan

Distinguishing Direct from Indirect - Summary Table

Assessing Complications on USG

Incarcerated Hernia

• Hernia contents cannot be reduced back into the abdomen
• Bowel loops appear non-peristaltic (absent real-time peristalsis)
• The hernia sac may contain fluid
• Apply gentle probe pressure - if sac is firm and non-reducible, incarceration is likely
• Look for bowel wall thickening, ascites, or dilated proximal bowel loops

Strangulated Hernia (Ischemic Bowel)

• Absent or reduced color Doppler flow in the bowel wall
• Thickened bowel wall (>3 mm)
• Free fluid in the sac
• Associated echogenic mesenteric fat (edema/ischemia)
• Clinical urgency - do not delay surgery for imaging

USG vs. CT in Emergencies

• POCUS is rapidly available; CT (sensitivity 90%, specificity 97%) is more definitive for incarcerated/strangulated cases
• If bowel is confidently identified in the sac with absent peristalsis and no Doppler flow, surgical consultation should not wait for CT

Postoperative USG

• Seroma - anechoic fluid collection at the repair site (common, usually resolves within 1 month)
• Hematoma - mixed echogenicity fluid collection
• Recurrence - hernia sac visible again at the repair site on Valsalva; mesh may appear as a hyperechoic structure

Differential Diagnosis of Inguinal Region Mass (USG)

Key Clinical Tips

1. Always scan with Valsalva - many hernias only appear with increased intra-abdominal pressure
2. Stand the patient up if supine Valsalva is negative but clinical suspicion is high
3. Identify the IEA with color Doppler first - this is the key landmark for direct vs. indirect classification
4. Assess both sides - contralateral hernia is common (50% lifetime risk on the other side)
5. Female patients: the canal of Nuck (patent processus vaginalis) makes indirect hernias possible; Doppler is especially important as there is no spermatic cord reference structure
6. Real-time peristalsis = bowel in sac - this finding alone in the inguinal region is diagnostic of bowel-containing hernia

Grainger & Allison's Diagnostic Radiology - Library Reference

Bibliographic Details

Editors

Content Coverage by Block (Library)

Key Features of the 7th Edition

• 2,400 pages across 2 volumes; >4,000 high-quality illustrations
• Covers the entire spectrum of imaging modalities: X-ray, CT, MRI, Ultrasound, Nuclear medicine, PET-CT, SPECT, Fluoroscopy, Angiography, Interventional radiology
• Organized on an organ and systems basis with integrated, correlative coverage of all imaging modalities
• Expanded cardiac imaging section covering cardiac MRI, 3D ultrasound, PET, and SPECT
• Functional and molecular imaging integrated throughout each section
• Includes latest image-guided biopsy and ablation techniques
• Intended audience: Radiologists in training and in practice; ideal for board/FRCR examination preparation

How to Cite (APA)

Adam, A., Dixon, A. K., Gillard, J. H., & Schaefer-Prokop, C. (Eds.). (2021). Grainger & Allison's diagnostic radiology: A textbook of medical imaging (7th ed.). Elsevier.

How to Search This Textbook in the Library

-- Search by topic (paragraph full-text)
SELECT section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end,
       snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 30) AS snippet
FROM paragraphs_fts
WHERE paragraphs_fts MATCH 'your topic here'
  AND book_isbn = '9780323760751'
ORDER BY rank LIMIT 10;

-- Browse table of contents
SELECT heading, block_number, line_number
FROM v_toc
WHERE book_isbn = '9780323760751'
ORDER BY block_number, line_number;

Liposarcoma - Ultrasound (USG)

Overview

WHO Subtypes and USG Characteristics

General USG Features of Liposarcoma

• Usually hyperechoic for well-differentiated types (fat content); can be highly reflective on B-mode
• Retroperitoneal liposarcomas: highly echogenic mass with anterior displacement of viscera (pancreas, aorta, IVC, kidneys, colon)
• Heterogeneous echo pattern with echo-poor centre = necrosis/haemorrhage (tumour outgrows blood supply) - strongly suggests sarcoma
• >25% non-fat component within a fatty mass = consider liposarcoma over lipoma
• Doppler: liposarcoma is more vascular than lipoma - internal vascularity on colour Doppler distinguishes the two
• USG is limited in full characterisation - MRI is the definitive modality; CT for staging

USG Red Flag Features (Distinguish from Lipoma)

USG Images

1. Mayo Clinic Summary - Key USG Features of Liposarcoma

2. Retroperitoneal Liposarcoma - USG Scan

3. Liposarcoma Subtypes - USG Comparison Panel (B-mode + Doppler)

• (a, c, e) B-mode images showing varying echogenicity
• (b) Power Doppler showing rich internal vascularity in a high-grade lesion
• (d) Colour Doppler showing focal internal flow
• (e, f) Well-differentiated subtype - relatively homogeneous, hyperechoic, elongated mass

4. Well-Differentiated Liposarcoma - USG vs. Lipoma

5. Retroperitoneal Liposarcoma - CT for Correlation

6. MRI Subtype Comparison (for Radiological Correlation)

• (a) Myxoid liposarcoma - T1 dark (fluid-like myxoid stroma, arrowheads)
• (b) Dedifferentiated liposarcoma - biphasic mass with fatty and non-lipomatous nodule
• (c) Atypical lipoma/well-differentiated
• (d) Well-differentiated liposarcoma

Subtype-Specific USG Notes

Well-Differentiated / ALT

• Most common subtype; predominantly hyperechoic (fatty)
• Thickened or nodular septa and non-fat globular areas are the key red flags over benign lipoma
• Deep location (intramuscular, retroperitoneal) alone raises suspicion
• Size >10 cm, fat content <75% favour malignancy
• Doppler shows more vascularity than a lipoma

Myxoid Liposarcoma

• Contains abundant myxoid stroma (mucopolysaccharide-rich)
• On USG: hypoechoic to anechoic, may appear pseudocystic - can mimic a ganglion or simple cyst
• Posterior acoustic enhancement may be seen
• Subtle hyperechoic thin septa within the "cyst-like" area is a clue
• Unique metastatic pattern: retroperitoneum, spine (CT abdomen/pelvis and paraspinal MRI needed for staging)

Dedifferentiated Liposarcoma

• Biphasic appearance: a fatty (hyperechoic) component + a distinct solid hypoechoic non-lipomatous mass
• The solid component represents the dedifferentiated (high-grade) area
• Commonly in retroperitoneum; risk of dedifferentiation highest there (~10% of WDL)
• Doppler: internal vascularity in the solid component

Pleomorphic Liposarcoma

• Rare, high-grade
• Markedly heterogeneous, predominantly hypoechoic/solid mass with irregular margins
• Areas of central necrosis (echo-poor centre)
• Little to no identifiable fat on USG
• Rich internal vascularity on Doppler
• Indistinguishable from other high-grade soft tissue sarcomas on USG alone

Practical USG Approach

1. Any deep soft tissue mass >5 cm - treat as sarcoma until proven otherwise; refer to specialist centre
2. Retroperitoneal fatty mass - in contrast to extremities, lipomas are rare in retroperitoneum; assume liposarcoma until proven otherwise
3. Document echogenicity, septa thickness, non-fat components, margins, depth, size
4. Always apply colour/power Doppler - vascularity pattern is key in differentiating liposarcoma from lipoma
5. USG-guided biopsy - core needle biopsy (not FNA) is required; target the solid/non-fat component for histological diagnosis (avoid purely fatty areas - may give false negative)
6. After USG: proceed to MRI with contrast for definitive tissue characterisation and surgical planning