Anatomical Aspects of Infections

Anatomical Aspects of Infections

Anatomical Aspects of Infections

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Routes of Spread - Pathogen Parade

  • Hematogenous: Via bloodstream (arteries, veins); distant spread. E.g., sepsis, osteomyelitis.
  • Lymphatic: Via lymph channels to nodes; regional spread. E.g., TB, filariasis.
  • Direct Extension: Invasion of adjacent tissues/organs. E.g., cellulitis, sinusitis to orbit.
  • Along Fascial Planes: Tracks via low-resistance paths. E.g., Ludwig's angina, necrotizing fasciitis.
  • Perineural: Spread along nerve sheaths. E.g., rabies, VZV, perineural tumor spread.
  • Iatrogenic: From medical interventions. E.g., post-operative infections, contaminated devices.
  • Transplacental (Vertical): Mother to fetus via placenta. E.g., TORCH infections.
  • Canalicular: Along ducts/tubes. E.g., ascending UTI, cholangitis.

Spread of dental infections

⭐ Batson's plexus of veins (valveless) allows hematogenous spread of pelvic (e.g., prostate cancer) and abdominal infections/metastases to the vertebral column and brain.

Anatomical Barriers - Body's Border Control

  • Skin & Mucous Membranes: First line of defense.
    • Intact skin: Keratinized stratified squamous epithelium; physical barrier.
    • Mucous membranes: Line respiratory, GI, GU tracts; secrete mucus (traps pathogens), IgA.
    • Cilia: Respiratory tract; propel mucus & debris out.
  • Fascial Planes & Compartments: Limit spread of infection.
    • Deep fascia: Dense connective tissue; encloses muscle groups.
    • Intermuscular septa: Divide limbs into compartments.
    • Compromise (e.g., surgery, trauma) ↑ infection risk.
  • Body Fluids: Mechanical flushing & antimicrobial properties.
    • Tears, saliva, urine: Lysozyme, flushing action.

Anatomical & Physiological Barriers to Infection

⭐ Fascial planes often dictate the pathway of pus collection and spread; e.g., prevertebral fascia can allow infection spread from pharynx to posterior mediastinum or even diaphragm (Danger space).

Key Infected Spaces - Trouble Hotspots

  • Neck Spaces:
    • Retropharyngeal Space ("Danger Space"): Extends to posterior mediastinum. Risk of mediastinitis. Dysphagia, dyspnea.
    • Parapharyngeal Space: Lateral neck swelling, trismus. Carotid sheath contents at risk.
    • Ludwig's Angina: Bilateral infection of submandibular/sublingual/submental spaces. Woody induration, airway compromise. Sagittal CT of Ludwig's Angina
  • Hand Spaces:
    • Thenar Space: Thumb/index infections.
    • Midpalmar Space: Middle/ring/little finger infections.
    • Parona's Space (Forearm): Proximal spread from bursae.
    • 📌 Kanavel's Signs (Flexor Tenosynovitis): Finger flexed, Length tender, Extension painful, Symmetrical swelling.
  • Subphrenic Spaces:
    • Between diaphragm & transverse colon. Common post-laparotomy. Shoulder tip pain.
  • Ischiorectal Fossa (Perianal):
    • Lateral to anal canal. Common for abscesses. Painful perianal swelling.

⭐ Ludwig's angina is a rapidly spreading cellulitis of the floor of the mouth that can cause acute airway obstruction; a surgical emergency.

Organ-Specific Infections - Systemic Weak Spots

  • Liver Abscesses:
    • Pyogenic: Portal vein (e.g., appendicitis); R lobe common (portal flow).
    • Amoebic: E. histolytica; "anchovy sauce" pus; often single, R lobe.
  • Lung Infections:
    • Aspiration Pneumonia: Gravity-dependent sites (posterior segments of upper lobes, superior segments of lower lobes).
    • Tuberculosis (TB): Apices (↑O2 tension, ↓lymphatic drainage).
  • Brain Infections:
    • Abscess: Hematogenous (grey-white matter junction); direct extension (e.g., sinusitis, otitis).
    • Cavernous Sinus Thrombosis: Valveless facial veins drain via ophthalmic veins ("danger triangle" of face).
  • Osteomyelitis:
    • Children: Long bone metaphysis (rich vascularity, hairpin capillary loops, sluggish flow).
    • Adults: Vertebrae (Batson's venous plexus allows spread from pelvic/prostatic infections).
  • Kidney (Pyelonephritis):
    • Ascending infection from lower UTI; Vesicoureteral Reflux (VUR) is a key risk factor.
    • Renal carbuncle: Staphylococcal cortical abscess, often hematogenous.

⭐ Batson's plexus, a network of valveless veins, facilitates the hematogenous spread of pelvic or prostatic infections/malignancies to the vertebral column, leading to osteomyelitis or metastases an important concept for understanding spinal infections and cancer spread.

High‑Yield Points - ⚡ Biggest Takeaways

  • Danger triangle of face drains to cavernous sinus via ophthalmic veins; risk of septic thrombosis.
  • Ludwig's angina: cellulitis of submandibular, sublingual, submental spaces; airway compromise risk.
  • Retropharyngeal space infections ("danger space") can rapidly spread to posterior mediastinum.
  • Psoas abscess, often from vertebral TB, tracks along psoas sheath to inguinal region.
  • Hand infections: Felon (fingertip pulp), paronychia (nail fold), tenosynovitis (Kanavel's signs).
  • Lymphatic drainage patterns dictate regional spread; e.g., axillary nodes from upper limb_

Practice Questions: Anatomical Aspects of Infections

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Most common route of nosocomial infection [Hospital-acquired infection]?

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Flashcards: Anatomical Aspects of Infections

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Foramen of _____ acts as a pathway for the spread of parotid or superficial mastoid infections to the canal or vice versa.

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Foramen of _____ acts as a pathway for the spread of parotid or superficial mastoid infections to the canal or vice versa.

Santorini

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