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
  • 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, parasthesias, muscle weakness, and hypotension
• Rarely severe envenomations can lead to death

Differential Diagnosis

Marine toxins, envenomations, and bites

• Toxins
  • Ciguatera
  • Neurotoxic shellfish poisoning
  • Paralytic shellfish poisoning
  • Scombroid
  • Tetrodotoxin (e.g. pufferfish)
• Stingers
  • Stingray injury
• Venomous fish (catfish, zebrafish, scorpion fish, stonefish)
  • Cone shells
  • Lionfish
  • Sea urchins
• Nematocysts
  • Coral reef
  • Fire coral
  • Jellyfish (Cnidaria)
    • Box jellyfish
    • Sea wasp
  • Portuguese man-of-war
  • Sea anemones
  • Seabather's eruption
• Phylum porifera (sponges)
• Bites
  • Alligator and crocodile attacks
  • Octopus bite
  • Shark bite
• Infections
  • Vibrio species in saltwater
  • Aeromonas species in freshwater

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

Complications

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

Disposition

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

See Also

• Marine toxins and envenomations
• Cone shells
• Lionfish