Infection caused by the larval stage of a tapeworm – usually Echinococcus granulosus.
Most commonly involves the liver (50 – 70 %) or lungs (20 – 30 %)
Kidney is most affected urological organ (2 – 4 %), with reports of prostate, testis, SV involvement.
Life cycle
The definitive host is the dog, with eggs passed in dog faeces.
Sheep are the usual intermediate host, but there can be direct transmission to humans.
Hydatid embryo penetrates duodenal mucosa and enters bloodstream.
Clinical features
Often asymptomatic, slowly growing 1 – 2 cm/yr, and may cause symptoms at large sizes (similar to renal mass – flank pain, palpable mass, haematuria).
One pathognomonic feature is passage of “grape-like” or grapeskin material in the urine (5 – 25 %)
Eosinophilia often present on bloods.
No easy confirmatory laboratory test – “indirect haemagglutination test” about 75 % positive rate.
Can rupture at large sizes – often very antigenic/can cause hypersensitivity or anaphylaxis reaction, and lead to new metastatic deposits.
Imaging
Ultrasound “double wall sign” due to dual layer, with possible daughter cysts involved.
CT often shows calcified wall, and daughter cysts. Usually thickened wall (due to inflammatory reaction) on CT/MRI.
Treatment
Surgical excision if appropriate with care to avoid spillage if possible.
Medical treatment with albendazole 400 mg BD can be used for a month neo-adjuvant and adjuvant.
Long term albendazole reported to be used if not amenable to operative intervention.
Retrovesical hydatid
May present as cystic pelvic structure – secondary to possible intraperitoneal or hepatic cyst rupture.
May mimic rectal duplication cyst, rectosigmoid tumour, posterior bladder diverticulum, seminal vesicle cyst, or ovarian cystic neoplasm.