Sea urchins

Background
  • Sea urchins are marine invertebrate echinoderms
  • Anatomy consists of soft viscera surrounded by a hard plated body with protruding spines and pedicellariae
  • Around 950 known species and some are venomous[1]
    • Nonvenomous species have blunt, rounded spines
    • Venomous species have sharp, hollow, thin spines
    • Some have pedicellariae with sharp jaws and venom glands

Mechanism
  • Nonvenomous spines cause direct trauma
  • Venoms are known to contain proteases, hemolysins, steroid glycosides, serotonin, cholinergic substances, and rarely neurotoxins
  • Pedicellariae attach to the victim and break off from the urchin, releasing venom for several hours

Clinical Features
Black sea urchins (Echinometra lucunter). Below: spinesin the feet of bathers. Right: hyperkeratotic noduleson the hands of a diver who suffered several injuries caused by black sea urchins (foreign body granuloma).
  • Minor to severe pain the the site of the embedded spine
  • Venomous spines and pedicellariae generally cause much more severe pain and may be accompanied by systemic signs and symptoms with a significant envenomation including pruritus, nausea, vomiting, abdominal pain, respiratory distress, paresthesias, muscle weakness, and hypotension
  • Rarely severe envenomations can lead to death


Differential Diagnosis

Marine toxins, envenomations, and bites

Evaluation
  • Clinical diagnosis
  • Plain films of the injured areas to locate embedded spines
    • Evaluate for intraarticular spines
    • Ultrasound may be useful if none are seen but radiolucent FB is suspected
    • MRI can also locate spines not seen on plain film

Management
  • Emersion in non-scalding water up to 45°C
  • Prompt removal of pedicellariae
  • Remove spines/foreign bodies
    • If spines are intraarticular or near neurovascular structures they need to be carefully removed in the OR
  • Thorough irrigation
  • Update tetanus vaccination if needed
  • Prophylactic antibiotics for deep puncture wounds

Disposition
  • Depends on the extent and location of injury and degree of envenomation

Complications
  • Retained spines
  • Infection (Vibrio species)
  • Granuloma and cyst formation

See Also


References
  1. Auerbach P. Chapter 73. Envenomation by aquatic invertebrates. In: Auerbach P. Wilderness Medicine.
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