In male dogs, the prostate gland is a two-lobed structure that surrounds the proximal part of the urethra near the urinary bladder (UB). The prostate gland is the only accessory sexual organ in male dogs (1,10,11,14). Diseases of the prostate gland are relatively common in dogs, particularly in middle-aged to older unneutered dogs (2). These conditions include benign prostatic hyperplasia (BPH), prostatitis, prostatic cysts, and neoplasia of the prostate (22). BPH, prostatitis, and cysts are the most common disorders of the prostate, whereas, prostatic abscesses, neoplasms, and hematomas are relatively uncommon (16). Multiple cystic changes within and on the surface of the prostate are common in BPH; however, the occurrence of a large single cyst is uncommon, and its cause remains unclear. The etiology is postulated to involve the development of microcysts resulting from ductal obstruction as well as the accumulation of secretions due to obstructed drainage (14). A cyst within or adjacent to the prostate gland is known as a prostatic cyst, which can be either within or attached to the prostate. There are two types of prostatic cysts: parenchymal cysts related to prostatic hyperplasia and paraprostatic cysts (PPC) attached to the prostate, and may have a connection (12).

PPC are relatively uncommon compared to other prostatic conditions. These cysts are located and attached to the prostate, but communicate infrequently with the parenchyma (12). PPC are embryologically known to represent male malformations caused by remnants of Müllerian ducts. However, this has not been clearly demonstrated in dogs (25). PPC are commonly significant in size and may extend into the surrounding areas of the perineal fossa or abdomen. Extension of the PPC can result in the displacement and disruption of nearby organs and their functions. Histologically, the cyst walls exhibit characteristics similar to those of parenchymal cysts, including a compressed epithelium and dense collagen. In some cases, the walls may have been calcified. It is also possible that prostatic cysts become infected and form abscesses. Excessive pressure on the pelvic diaphragm may also play a role in the development of perineal hernia (12). These cystic lesions of the prostate can cause size-dependent clinical symptoms including dysuria, defecation disorder, penile discharge, and tenesmus (1).

This case report describes the medical history and clinical examination of a patient who underwent subtotal resection of the PPC, leaving two sites of remnants because the anatomical approach was very challenging. The surgical technique, postoperative care, and outcome of the procedure were also described.

A 6-year-old intact male Cane Corso dog weighing 40 kg presented to the Veterinary Medical Teaching Hospital of Jeju National University with a 2-month history of dysuria, dyschezia, anorexia, intermittent panting, abdominal distension, and penile discharge.

Abdominal radiography revealed an oval soft-tissue opaque mass in the mid-to-caudal region of the abdomen. The mass caused a dorsal displacement of the descending colon and compression of the intestines in the cranial and peripheral directions. The UB was indistinct because of the presence of the mass. Abdominal ultrasonography revealed a cystic mass close to the prostate gland. Due to its size, it was not possible to fully evaluate the mass using ultrasound alone. For more details regarding the mass and the plan for surgical intervention, computed tomography (CT) scans of the abdominal and pelvic regions were performed. Computed tomography (CT) revealed a significant fluid-filled structure, causing displacement of the UB, prostate, and descending colon, with an approximate size of 25 cm × 14 cm × 9 cm (Fig. 1A). Furthermore, the mass appeared to be connected to the ventral aspect of the right prostate lobe. In addition, increased opacity and mineralized tissue were observed in the dorsolateral aspect of the rectum within the pelvic cavity, which was connected to the mass (Fig. 1B). The margins of the mass were identified as being irregularly contrast-enhanced and mineralized. Through imaging, a diagnosis of PPC was made, and accordingly, an operation was planned.

Figure 1. Dorsal and sagittal CT images of a giant paraprostatic cyst located in the abdominal cavity of a dog. (A) A large fluid-filled cyst-like lesion approximately 25 cm in length and 9 cm in height. The cyst is mineralized along the wall, heterogenous contrast enhancement confirmed. The cyst shows continuity with the mineralized tissue in the pelvic region around the rectum. (white arrow) (B) The cyst is approximately 14 cm width and showing continuity with enlarged prostate gland.

On the day of the operation (day 0), the patient’s body weight was 40 kg, and systolic blood pressure, body temperature, pulse, and respiratory rate were all normal. Infiltration anesthesia was induced using lidocaine hydrochloride (Lidocaine HCl Hydrate Inj. 2%^®, Daihan, Korea) on the linea alba. RLK (remifentanil hydrochloride 5 g/kg/h; Remiva Inj^®, Hana Pharm Co., Korea, lidocaine hydrochloride 1 mg/kg/h; ketamine hydrochloride 0.12 mg/kg/h; Ketamine 50 Inj^®, YUHAN, Korea) continuous rate infusion (CRI) was used for intraoperative analgesia. After induction with propofol (4 mg/kg, intravenously; Anepol Inj^®., Hana Pharm Co., Korea), endotracheal intubation was performed to maintain anesthesia with isoflurane (Ifran^®, Hana Pharm Co., Korea).

The operation was initiated through an incision along the linea alba from the umbilicus to the right side of the penis. The structures within the abdominal cavity, including the intestine, were explored, and the UB and giant PPC were identified. The PPC was connected to the UB and right lobe of the prostate gland by soft tissue.

The PPC was covered by the omentum and was well vascularized. It was large and oval-shaped, and when palpated and shaken, a cavity filled with fluid was observed. The texture was similar to tough, hard leather or cartilage, and was far from soft tissue in general. Its approximate size was 20 cm × 20 cm × 10 cm (Fig. 2A). Prior to excision and separation of the PPC, to preserve the ureter connected from each kidney to the UB, it was identified and retracted using nylon tape. Subsequently, resection was attempted along the border of the PPC, along with part of the omentum covering the PPC, and decompression was attempted through a stab incision for convenience of the operation. The PPC was filled with a pus-like fluid, approximately 2 L of which was removed. The soft tissue between the PPC and UB was successfully separated by blunt dissection.

Figure 2. Intraoperative pictures of paraprostatic cyst and omentalization. (A) Paraprostatic cyst was isolated from the abdominal cavity. The cyst was large, fluid-filled, hard, rough texture, and well-vascularized. (B) Paraprostatic cyst was subtotally resected. (C) Omentum (dotted white arrow) was pulled into the stump of prostate gland (white arrow) and secured.

A diverticulum-like lesion was visually confirmed in the ventral part of the UB body. Upon stab incision, the lumen of the lesion was filled with pus-like fluid and did not communicate with the lumen of the UB. The lesion had an abscess-like appearance in the pus. Partial cystectomy, including the lesion, was performed.

It was confirmed that the right lobe of the prostate gland was visually enlarged in the caudal part along the UB and was adhered to the PPC by soft tissue. Subsequent blunt dissection of the soft tissue revealed communication between the lumen of the PPC and prostate parenchyma. In addition, blind palpation confirmed that the dorsolateral tissue adjacent to the rectum in the pelvic cavity, which showed increased opacity and mineralization on the preoperative CT scan, also had continuity with the PPC. Subtotal resection was performed, leaving two sites with PPC remnants (Fig. 2B). One site was the prostate gland, which communicated with and adhered to the PPC, and the other site was the pelvic region, where the PPC had spread. The reason for leaving two remnants was that an anatomical approach for complete resection was difficult, and complications associated with prostatic urethral damage were avoided. To reduce the risk of recurrence due to PPC remnants and promote rapid recovery, anti-inflammatory effects, and smooth drainage, the omentum was pulled into the remnants and secured to the resection site with absorbable suture material in a mattress pattern (Fig. 2C). After subtotal resection of the PPC and omentalization, castration was performed to reduce the enlarged prostate and prevent disease. The abdominal cavity was closed routinely, and the patient recovered smoothly from the anesthesia.

During hospitalization, the patient’s body weight was 37.2 kg; pain was managed through RLK CRI. The patient recovered well without any problems after the surgery; 4 hours after surgery, walked, and voluntarily urinated without assistance. 18 hours after surgery, the patient was discharged with a fentanyl patch (Fentanyl Patch 50 μg/h^®, Myungmoon, Korea, 2EA, 100 μg/h) attached, and oral medications were prescribed cephalexin (Phalexin^®, Dongwha, Korea, 20 mg/kg PO twice daily, 5 days) and meloxicam (Metacam^®, Boehringer Ingelheim, Germany, 0.1 mg/kg PO once daily, 5 days).

On Day 3, the patient’s appetite and vitality greatly recovered, and the symptoms of intermittent panting during waking and sleeping hours also improved. Apart from castration, tamsulosin (Tamsulosin HCl SR Tab^®, Boryung pharm, 0.4 mg, PO SID, 10 days) was additionally prescribed for reducing the size of the prostate gland and smooth voluntary urination.

On Day 14, the appetite, vitality, defecation, and urination were normal. The body weight was maintained at 36.8 kg. Ultrasonography revealed that the diameter of the prostate gland decreased significantly, hence tamsulosin was discontinued.

On Day 90, radiography, ultrasound, and CT scans showed that the size of the remnant remaining from the subtotal resection did not increase (Fig. 3), and there was no recurrence of clinical symptoms or occurrence of new clinical symptoms.

Figure 3. Dorsal and sagittal CT images of 90 days after the operation. Cyst remnants (white arrow) did not increase in size.

On Day 180, there were no complaints of any clinical symptoms of the patient upon telephonic follow-up.

The histopathological diagnosis was PPC with osseous metaplasia and necrotic granulation tissue which occurred as a metaplastic response due to chronic tissue damage caused by the extension of the PPC to the serosa and omentum (Fig. 4A). The affected ventral body of the UB was confirmed as acute and chronic necrotizing cystitis with abscess formation, whereas epithelial neoplasm was not confirmed (Fig. 4B). The resection margin area of the PPC along with the right lobe of the prostate gland was diagnosed as acute and chronic necrotizing cystitis and prostatitis with multifocal ossification (Fig. 4C). Both the intra-cystic and UB abscess fluids requested for cytological examination were identified as pus due to suppurative inflammation.

Figure 4. Histopathological micrographs of tissues sampled during the operation (H&E stain, original magnification x 200, Scale bar 200 μm). (A) Micrograph of PPC, fibrous stroma, smooth muscle wall, necrotic granulation tissue, and bone trabeculae lined by osteoblasts and osteoclasts. (B) Diverticulum-like lesion of the ventral part of the UB body excised by partial cystectomy, the muscular wall shows infiltration of necrotic neutrophils and macrophages. (C) The resection margin area of the mass with the right lobe of the prostate gland, irregular bone foci, and extensive ulceration of bladder mucosal epithelium with infiltrates of inflammatory cells over necrotic debris, granulation tissue, and fibrotic stroma.

This case report finding is similar to those reported in previous studies, which suggest that prostatic diseases are more common in middle-aged and older dogs, except for prostatic neoplasia, which is more common in larger than in small dogs and intact male dogs (7,15,18,20,22,23). The formation of prostatic cysts can be linked to BPH and occurs due to the obstruction of the canaliculi, which causes the accumulation of prostatic fluid. Prostatic cysts are common in dogs with coexisting BPH and other prostatic disorders (1,22). This is typically a large-breed dog that has not yet been neutered. At the time of diagnosis, the patient was 6 years 10 months old (i.e., middle- to old-aged). BPH was also confirmed as a concomitant disease through ultrasound, CT, and rectal palpation.

A previous study reported that approximately 50% of patients with prostatic diseases, including PPC, exhibit urinary symptoms such as hematuria, stranguria, and dysuria (18). Another study reported that, unlike in humans, dysuria, such as urinary retention, is not commonly observed in prostatic diseases other than those with large cavities and neoplasia in dogs (16). However, in the present case, the patient exhibited severe dysuria and was only able to urinate sufficiently through a urinary catheter for approximately 20 days before the operation. Additionally, previous studies have reported that complications such as urinary incontinence can be fairly frequent (22) in dogs following surgery for large prostatic cysts because of anatomical changes in the urethra resulting from the development of prostatic cysts (14). In this case, symptoms such as dysuria and urinary incontinence were alleviated, and voluntary urination was possible without the aid of a urinary catheter 1 day postoperatively. The patient was well-managed and had no postoperative complications or recurrence until day 180 of follow-up.

In recent years, treatment options for prostatic cysts in dogs have undergone significant changes. Minimally invasive treatments such as cyst aspiration, alcoholization, and platelet-rich plasma injection have been described (3,5,6,8). However, accurate indications for treatment have not been provided, and there is no comparison of treatment outcomes and prognosis with traditional surgical methods such as marsupialization, complete prostatectomy, and partial resection with omentalization. However, recently, marsupialization and complete prostatectomy have been found to have inadequate advantages compared to partial resection with omentalization, and are no longer recommended (13,19).

According to a recent study (9), 22.7% (11/44) of dogs with prostatic cysts were concurrently affected by a perineal hernia, and 11.4% (5/44) had testicular neoplasms. Despite the relatively high probability of comorbidities, perineal hernia or testicular neoplasms were not observed. Furthermore, in over 50% of the dogs, the size of the cysts was greater than 20 cm, and it would have been helpful if there had been a comparison of the correlation between the size of the cyst and the body size and weight of the dogs, as well as the degree of clinical symptoms according to cyst size.

In the present case, a severe UB abscess lesion requiring partial cystectomy was observed. Previous studies have confirmed that PPC and UB abscesses are distinct conditions. The factors presumed to cause the UB abscess, in this case, were that before the final diagnosis of PPC prior to the operation, fine-needle aspiration (FNA) and centesis were attempted blindly without ultrasound guidance; no significant cells were identified, and fluid also showed urine characteristics. This made the diagnosis of paraprostatic cyst challenging. Subsequent CT imaging revealed a giant PPC occupying most of the abdominal cavity, and it was thought that blind FNA and centesis could target the PPC. However, the actual location reached by the needle was a part of the UB, and this stimulation could have led to the development of a UB abscess.

Prostatic cysts are typically large nodular structures that can be palpated through the pelvic cavity and may reach up to 30 cm in diameter (17). They are surrounded by a tough fibrocollagenous capsule that can harden and mineralize (4,22), although this is uncommon (24,26,27). However, some studies have suggested that mineralization is more common than previously thought, with some cases reporting mineralized cysts in up to half of affected dogs (21). In patients with coexisting BPH, providing appropriate medications for BPH to patients during pre- and post-operative management for cyst removal and castration may result in more efficient and expedited relief of urinary symptoms.

Although there was no evidence of this in our case, sudden traction and decompression during the surgical removal of giant masses that cause mass effects by compressing adjacent structures within the abdominal cavity may result in maladaptive physiological changes in the patient’s vital signs. This is potentially life-threatening and should always be approached with caution.

Subtotal resection with omentalization and castration can successfully manage and treat PPC in dogs, even when multiple cyst remnants remain. This surgical intervention rapidly relieves clinical symptoms and is effective in the long term without complications or recurrence.

This work was supported by the 2023 education, research and student guidance grant funded by Jeju National University.

The authors have no conflicting interests.