Overview

• Prostatic cysts in the dog include those associated with diffuse epithelial cystic change from androgen-dependent benign prostatic hypertrophy, retention cysts within the prostatic parenchyma that are cavitating, fluid-filled lesions with a distinct capsule, and paraprostatic cysts that are cavitating, fluid-filled lesions with a distinct capsule located outside of the prostatic parenchyma. Prostatic cysts may range in diameter from a few mm to more than 20 cm.
• Paraprostatic cysts usually arise craniolateral to the prostate, displacing the bladder cranially and ventrally, or caudal to the prostate in the pelvis. Prostatic cysts may represent dilated embryonal remnants of the wolffian ducts.
• Pathogenesis is unknown, but the occurrence of retention cysts in dogs with estrogen-secreting Sertoli cell tumors causes speculation that these cysts are dilations of prostatic acini secondary to estrogen-induced squamous metaplasia.

Signalment

• Male intact dogs. Rare occurrence in castrated dogs
• Age range-2–12 years, mean age 8 years
• Large dogs are more commonly affected than small dogs

Signs

• Asymptomatic
• Lethargy and anorexia
• Abdominal distention
• Tenesmus if the cyst compresses the rectum
• Dysuria if the cyst compresses the urethra
• Sanguineous urethral discharge in the presence of BPH

Causes & Risk Factors

• Benign prostatic hypertrophy
• Androgenic hormones
• Estrogenic hormones

Differential Diagnosis

• BPH-distinguished by ultrasound.
• Prostatic abscess-distinguished by ultrasound and semen culture.
• Distended urinary bladder-distinguished by cystocentesis, imaging.
• Caudal abdominal mass of undetermined origin-distinguished by imaging.

CBC/Biochemistry/Urinalysis

No abnormalities

Other Laboratory Tests

• Examination of prostatic fluid collected by ejaculation or prostatic massage confirms absence of infection.
• Culture and cytology of cyst fluid collected by ultrasound-guided fine-needle aspiration or by aspiration at surgical exploration reveals sterile clear or sanguineous fluid consistent with prostatic fluid.

Imaging

Retrograde contrast urethrocystography followed by prostatic ultrasonography confirms presence, location, echo-texture, and size of prostatic cysts, and differentiates retention cysts from paraprostatic cysts.

Diagnostic Procedures

Collection of prostatic fluid by ejaculation followed by prostatic imaging is recommended prior to fine-needle aspiration of cystic fluid to rule-out bacterial infection.

Pathologic Findings

Epithelial cysts within the prostatic parenchyma occur with parenchymal hypertrophy and hyperplasia; squamous metaplasia of the ducts and alveoli may be present. Retention cysts and paraprostatic cysts are lined by a single layer of prostatic epithelium or fibrous connective tissue and contain clear to sanguineous fluid with fibrin.

Drug(s)

Prostatic parenchyma and diffuse epithelial cysts involute following treatment with the 5 alpha-reductase inhibitor finasteride (0.1–1 mg/kg PO q24h for 2–4 months). Finasteride prevents conversion of testosterone to dihydrotestosterone, causing prostatic involution without adversely affecting libido or spermatogenesis. BPH recurs following cessation of finasteride therapy. Paraprostatic cysts do not respond to finasteride treatment.

Contraindications/Possible Interactions

N/A

Abbreviation

• BPH = benign prostatic hypertrophy

Author Carl A. Osborne

Consulting Editor Carl A. Osborne

Acknowledgment The author and editors would like to acknowledge the prior contribution of Margaret V. Root Kustritz.