Conference 02 - 2025 Case: 02 20250827

Wednesday Slide Conference, 2025-2026, Conference 2, Case 2

Signalment:

10 year old male rhesus macaque (Macaca mulatta)

History:

This animal was received from a U.C. Davis colony in October of 2018, and was subsequently used on malaria and dengue studies. The last routine physical performed in December 2023, where it was noted that this animal was missing the tips of the left and right pinna, and there was unspecified dental disease.

During 02 February 2024 cage-side rounds examination, this animal was noted to be staring at a resident too intently, and a sedated exam was elected to investigate further. Moderate abdominal distention was noted when the animal was placed in dorsal recumbency. A firm bladder was palpated on physical exam, and animal caretakers noted that there was low urine production for this animal. Ultrasound and radiographs showed a large bladder with no obvious blockage, and medical management was elected over the weekend.

On 05 February 2024, this animal’s clinical signs persisted, and a cystotomy was performed. A large amount of friable, tan-brown irregularly shaped to molded round material was removed from the urinary bladder. The material had a foul odor and was suspected to have a significant bacterial component. The luminal material was sent for culture and sensitivity, a section was used to make a smear cytology, and H&E slides. The results of preliminary diagnostics are below.

This animal recovered, and approximately one month later was euthanized as part of a protocol and was submitted for necropsy. The submitted slides were created from materials collected at necropsy.

Gross Pathology:

There is moderate abdominal distension in dorsal recumbency. Lateral radiographs show a moderate amount of heterogenous material at the cranial aspect of the urinary bladder, having irregular margins and poor contrast against surrounding tissue. Urinary catheter placement was difficult due to suspected narrowing of the urethra. Contrast material did not uniformly highlight the margins of the urinary bladder. A 60 cc syringe was used to remove normal colored urine from the distended urinary bladder.

Gross examination of the urinary bladder during exploratory surgery revealed congested serosal vessels, and mild erythema of the detrusor muscle. The urinary bladder wall is markedly thickened at approximately 1 cm thickness. There is multifocal friable, irregularly tan-brown material in the lumen of the urinary bladder, which emits an odor consistent with bacterial infection.

On subsequent necropsy, there is approximately 20 mL of blood in the abdomen. There are multifocal adhesions from the lateral and ventral aspect of the urinary bladder to the body wall. The urinary bladder appears mildly thickened. There is tan-brown irregular friable material within the lumen of the urinary bladder, and the urothelial mucosa is characterized by mild multifocal petechial hemorrhage.

Laboratory Results:

Cytology: These good quality, moderately cellular cytologic specimens contain mature sperm, rafts of 1-2 µm basophilic cocci, 1-2 µm x 1 µm bacilli, aggregates of extracellular matrix, infrequent macrophages, and necrotic material, overlying a faintly basophilic proteinaceous background. Sperm most often consist of only the head, with acrosome surrounding a variably intact nucleus, and measuring approximately 3 µm x 4 µm, with a polar oriented basophilia. Numerous sperm also contain the centriole and tail intact. Macrophages most often have abundant cytoplasm densely packed with cocci and bacilli, and few have multiple peripheralized nuclei (multinucleated giant cells).

A coagulum of material was processed for routine H&E evaluation. Multifocal colonies of gram-positive coccobacilli are visualized embedded in the extracellular proteinaceous material. Culture and initial identification was performed using MALDI. The isolate was small, pleomorphic, gram positive bacilli that are catalase positive and oxidase negative. An initial identification of Corynebacterium confusum was made.

Sensitivity testing indicated the following:

Antimicrobial	Result
Tetracycline	S
Levofloxacin	R
Amoxicillin Clavulanic Acid	S
Erythromycin	S
Chloramphenicol	NA
Nitrofurantoin	NA
Sulfamethoxazole Trimethoprim	NA
Oxacillin	R
Ciprofloxacin	R
Vancomycin	S
Cefazolin	S
Clindamycin	NA
Gentamicin	S
Polymyxin B	I

S: Sensitive; I: Intermediate; R: Resistant

After whole genome sequencing, the isolate was identified as Corynebacterium renale.

Microscopic Description:

Occupying approximately 90% of the markedly dilated prostatic urethra is a round, 13 mm diameter cross section of a heterogenous plug, composed of eosinophilic extracellular protein, variably mature fibrin, collagen, and numerous macrophages surrounding or centered on spermatids. The fibrin and collagen vary from compact, to basketweave appearance, and there is multifocal mineralization.

The prostatic urothelium is attenuated, with multifocal ulceration. Multifocal degenerating urothelial cells are characterized by moderate to marked cytoplasmic vacuolation, with neutrophils transmigrating the urothelium. The underlying lamina propria has multifocal to coalescing hemorrhage, edema, and perivascular to diffuse neutrophilic urethritis. Multifocal myocytes are characterized by hypereosinophilia, sarcoplasmic vacuolation, and/or pyknotic nuclei.

The glands of the ventral prostate are multifocally ectatic, occasionally filled with eosinophilic proteinaceous material admixed with necrotic neutrophils and macrophages. Glandular epithelial cells are multifocally attenuated, vacuolated (degenerate), or necrotic, with multifocal neutrophilic inflammation surrounding glands and overlying regions of increased fibrosis. There are multiple corpora amylacea within glands.

Contributor's Morphologic Diagnoses:

Prostatic urethra: Plug, proteinaceous, with urethral dilatation, moderate neutrophilic urethritis, moderate multifocal hemorrhage, and smooth muscle degeneration and necrosis.
(Not submitted) Urinary bladder: Cystitis, neutrophilic and eosinophilic, multifocal to coalescing, acute, mild, with urothelial degeneration and erosion, edema, and retrograde ejaculation coagulum.
(Not submitted) Seminal vesicle: Dilation, multifocal, mild, with multifocal aggregates of
(Not submitted) Kidney, left; kidney, right: Dilation, renal pelvis, moderate, with papillary necrosis, tubular epithelial necrosis, and dilation of Bowman’s space.
Ventral prostate: Prostatitis, lymphocytic and neutrophilic, multifocal, moderate, with multifocal corpora amylacea, and regional glandular
(Not submitted) Testis, seminiferous tubules: Degeneration, multifocal, moderate, with moderate ectasia.

Contributor's Comment:

Retrograde ejaculation cystolithiasis is an uncommon, but previously reported, affliction of nonhuman primates. This condition has been associated with repeated electroejaculation events; however, spontaneous disease has also been reported, as in this case.³ In most cases, clinical signs include stranguria, dysuria, hematuria, lethargy, and distended abdomen. This animal was fortunate to have forged a close relationship with the residents and communicated his distress non-verbally.

In the 1985 seminal work on electrostimulation and penile erection, it was shown that in canines and macaques (pigtail and Rhesus) the spinal nucleus responsible for erection is the mediolateral autonomic neurons in the T₁₂-L₃, and S₁-S₃ locations. However, stimulation of these nerves does not generally result in ejaculation.⁵ During normal ejaculation, there are two physiologically synchronized events controlled by sympathetic nerves. Emission and expulsion of ejaculate are distinct processes, and even minor alterations may adversely affect the animal. The expulsion process requires both urethral and penile muscle tissue to contract, allowing for the correct flow of fluid. If the internal urethral sphincter in the urinary bladder does not contract completely, reflux of fluid may occur and is called retrograde ejaculation. Retrograde ejaculation has been reported in numerous domestic species, as well as non-human primates. However, in non-human primates, the condition has most often been associated with electroejaculation, likely caused by asynchronous stimulation of nerve bundles. In these primates, the deposition of coagulum in the posterior urethra results in continued retrograde flow of semen into the urinary bladder. This has been reported in Rhesus macaques (Macaca mulatta) and cynomolgus macaques (Macaca fascicularis)¹, though usually without cystolithiasis in cynomolgus monkeys.⁴

The composition of semen impacts the possible degree of compromise in these cases. Ejaculate is comprised of sperm suspended in a fibrinous material produced by the accessory sex glands. The consistency of ejaculate changes based on the balance of coagulation and fibrinolytic factors present, and different ratios exist for different species. In humans, the balance of fibrinogen, factor VIII:c, plasminogen, antithrombin III, fibrin monomers, and plasminogen activator inhibitor-1 is critical, and altered ratios of D-dimer/thrombinantithrombin-III ratios have been detected post-vasectomy and in some cases of involuntary infertility.⁸ For the human patient, after discharge from the urethra, semen normally takes on a gelatinous consistency, but will turn to liquid again after 3 to 30 minutes.⁷ This is due to fibrinolysin contributed by the prostate, and this degradation does not occur in Rhesus macaques due to lower fibrinolytic activity and no fibrinolysin.³

In this animal, there was no history of electroejaculation. However, also considered were conditions that affect the competency of the urethral sphincter, and included congenital malformation, spinal cord damage or disease, previous urinary bladder surgery, or chronic inflammation. This event appears to be idiopathic, with no predisposing cause identified.

Unfortunately for this animal, a concurrent bacterial infection colonized the proteinaceous coagulum. There was spirited debate about the order in which events took place, and a primary bacterial infection leading to retrograde ejaculation cystolithiasis cannot be definitively excluded. However, the specific location of the plug and accompanying clinical signs support a primary retrograde ejaculation cystolithiasis with secondary bacterial infection. Regardless of event order, the observed cystitis and hydronephrosis are common findings accompanying cystolithiasis and urinary obstruction.

Contributing Institution:

Walter Reed Army Institute of Research, Silver Spring, MD

JPC Diagnoses:

Prostatic urethra: Seminal plug, chronic, with diffuse, mild, neutrophilic and eosinophilic urethritis and skeletal muscle atrophy.

JPC Comment:

The contributor provides a thorough overview of this entity in non-human primates in their comment! Conference discussion touched on several important topics mentioned in the contributor’s write-up, as well as provided a review of the differences in terminology between spermatids, spermatozoa, and sperm. Spermatids are the developing, immature form of spermatozoa. Spermatozoa are the mature form that has an acrosome and a tail. The term “sperm” refers to the whole ejaculate that contains spermatozoa and other fluid components.

Another species in which a similar condition occurs is mice. Known as Mouse Urologic Syndrome (MUS), it is characterized as an obstructive genitourinary condition in male mice resulting from a urethral blockage composed of a white-yellow protein-rich plug resembling seminal vesicular gland secretions (the copulatory plug). Histologically, these plugs are composed of a proteinaceous coagulum with mixed inflammatory cells, spermatozoa, and sloughed urothelial cells, which can become impacted within the urethral bulb, urethra, or urinary bladder. This can lead to urinary bladder distension, edema, complete pelvic or penile urethral blockage, paraphimosis, penile ulceration, and/or lethal hydronephrosis.⁶

The flexed anatomy of the penis in male mice, along with the pressure placed on the urethra from surrounding tissues and the ability of the seminal fluids to rapidly coagulate to form the copulatory plug, are thought to be contributory to the formation of MUS.⁶ Histologically, seminal coagulum plugs have been associated with urothelial erosion, congestion, and inflammation, which are consistent with prolonged pressure injury.⁹ Certain strains of mice are more predisposed to the development of MUS than others, including the male epileptic EL strain, STR/1N¹⁰ strain, and obese diabetic KK-A^y strain.⁹ This study also found that there was an increased incidence of MUS with medetomidine-ketamine anesthesia in C57/B6 and mixed genetic background strains due to the release of seminal fluids during anesthetic events with these medications. When their protocol was altered to xylazine-ketamine, the mice did not develop MUS.⁹

Something to be aware of when diagnosing MUS is that careful consideration must be given to the presence of other confirmatory lesions outside of the presence of a urethral plug. It is well known that mice will also release agonal nonobstructive plugs during death, so differentiating these from obstructive antemortem plugs is crucial in the diagnosis of MUS.^6,9 In an effort to standardize their criteria, one study utilized the presence of histologic urethritis, clinical azotemia, and gross/histologic hydronephrosis or renal cortical dilation to help them diagnose MUS vs agonal secretion.⁹

As a closing “fun fact”, one of Dr. Williams’ rules of engagement for today’s conference was that each case presenter had to bring him a fact about their assigned entity that he did not know. The presenter for this case successfully found such a fact and stated that other species that produce a copulatory plug include butterflies, spiders, scorpions, cats, kangaroos, and Madagascar hissing cockroaches. The more you know…

References:

Chandolia RK, Luetjens CM, Wistuba J, Semjonow A, Puhse G, Nieschlag E. Blockage of urine by intravesical ejaculate in cynomolgus monkeys. J Med Promatol. 2007;36:21-24.
Cline JM, Brignolo L, Ford EW. Urogenital System. In: Abee CR, Mansfield K, Tardiff S, Morris T, eds. Nonhuman primates in medical research, Vol. 2, 2^nd San Diego, CA: Academic Press; 2012:p 494.
Colman K, Andrews RN, Atkins H, et al. International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and proliferative lesions of the non-human primate (M. fascicularis). J Toxicol Pathol. 2021;34(3 Suppl):1S-182S.
Gumber S, Courtney CL, Strait KR, Sharma P, Freebersyser JE, Crane MM. Retrograde ejaculation associated spontaneous sperm cystolithiasis in four Rhesus Macaques (Macaca mulatta). Exp Toxicol Pathol. 2013. 65(0):1121-1125.
Lue TF, Schmidt RA, Tanagho EA. Electrostimulation and penile erection. Urol.Int. 1985;40:60-64.
Ninomiya H, Inomata T, Ogihara K. Obstructive uropathy and hydronephrosis in male KK-Ay mice: a report of cases. J Vet Med Sci. 1999 Jan;61(1):53-7.
Rasmussen J, Albrechtsen OK. Fibrinolytic activity in human seminal plasma. Fertility and Sterility. 1960;11(3):264277.
van Wersch JW, de Vries-Hanje JC, Ubachs JM. Coagulation and fibrinolysis markers in seminal plasma of patients under evaluation for involuntary childlessness. Eur I Clin Chem Clin Biochem. 1992;30(8):467-71.
Wells S, Trower C, Hough TA, Stewart M, Cheeseman MT. Urethral obstruction by seminal coagulum is associated with medetomidine-ketamine anesthesia in male mice on C57BL/6J and mixed genetic backgrounds. J Am Assoc Lab Anim Sci.2009;48(3):296-9.