Oophoritis and Ovarian Abscess

Oophoritis is an inflammatory condition of the ovary, which can be acute or chronic, and may be unilateral or bilateral. It is often associated with infection, but can also result from autoimmune, traumatic, or neoplastic processes. Ovarian abscess is a localized collection of pus within the ovarian parenchyma, typically resulting from bacterial infection, and can be a sequela of oophoritis. In domestic animals, particularly bitches and queens, oophoritis and ovarian abscess are rare but serious conditions that can lead to systemic illness, infertility, and potentially life-threatening complications such as peritonitis or septicemia. The condition may be primary or secondary to ascending infections from the reproductive tract, hematogenous spread, or iatrogenic causes. Clinically, it can present with vague signs such as lethargy, fever, abdominal pain, and reproductive disturbances, and may be an incidental finding during diagnostic imaging or ovariohysterectomy. Accurate diagnosis requires a combination of imaging, cytology, culture, and histopathology. Treatment typically involves surgical removal of the affected ovary (ovariectomy or ovariohysterectomy) along with appropriate antimicrobial therapy, and supportive care. Prognosis is generally good with early intervention, but can be guarded if complications such as peritonitis or sepsis develop.

The etiology of oophoritis and ovarian abscess in small animals is multifactorial. The most common causative agents are bacteria, with Escherichia coli, Streptococcus spp., Staphylococcus spp., and anaerobic organisms such as Bacteroides and Fusobacterium being frequently isolated. These pathogens can ascend from the lower reproductive tract, particularly in cases of vaginitis, metritis, or pyometra, or can spread hematogenously from distant sites of infection. Iatrogenic causes include contamination during surgical procedures, such as ovariohysterectomy or cesarean section, or during reproductive techniques like artificial insemination or embryo transfer. Trauma to the ovary, such as from abdominal trauma or rough palpation, can also predispose to inflammation and abscess formation. In some cases, oophoritis may be sterile, resulting from autoimmune reactions, where the immune system mistakenly attacks ovarian tissue, or from chemical irritation. Additionally, ovarian neoplasia, such as granulosa cell tumors, can undergo necrosis and secondary infection, leading to abscess formation. Hormonal factors, particularly elevated progesterone levels during diestrus, can create a favorable environment for bacterial growth by suppressing local immune responses and altering the uterine environment, which may facilitate ascending infections. In cats, feline infectious peritonitis (FIP) and other viral infections have been implicated in granulomatous oophoritis. Parasitic infections, such as toxoplasmosis, are rare but possible causes. The exact pathogenesis often involves a combination of bacterial virulence factors, host immune status, and local tissue factors.

Oophoritis and ovarian abscess are uncommon conditions in canine and feline patients. There is no strong breed predisposition, but any breed can be affected. The condition is more frequently diagnosed in intact adult females, typically between 2 to 8 years of age, coinciding with active reproductive cycles. Nulliparous animals may be at slightly higher risk due to repeated estrous cycles without pregnancy, which can lead to endometrial changes and increased susceptibility to infection. However, the condition can also occur in pregnant or postpartum animals, especially if there is uterine infection or retained fetal membranes. In breeding kennels or catteries, poor hygiene and high stocking density can increase the risk of infectious spread. The use of exogenous hormones, such as progestins for estrus suppression, has been associated with an increased risk of uterine and ovarian infections, including abscesses. Additionally, animals with a history of reproductive tract infections, such as pyometra, are at higher risk for developing oophoritis. The incidence is higher in dogs than in cats, possibly due to differences in reproductive physiology and management. In a retrospective study of ovarian lesions in dogs, oophoritis was found in approximately 2% of cases, while ovarian abscesses were even rarer. The condition is often underdiagnosed because it may be asymptomatic or present with nonspecific signs, and it is frequently discovered incidentally during ovariohysterectomy or on histopathological examination.

The pathophysiology of oophoritis and ovarian abscess involves a complex interplay between infectious agents, host immune responses, and hormonal influences. In bacterial oophoritis, the infection typically ascends from the lower reproductive tract through the uterus and uterine tubes (fallopian tubes) to reach the ovary. The presence of a purulent exudate within the uterine lumen, as seen in pyometra, can facilitate the spread of bacteria to the ovarian bursa and parenchyma. Alternatively, hematogenous spread can occur, where bacteria from a distant site, such as the skin, respiratory tract, or urinary tract, enter the bloodstream and seed the ovary. Once in the ovarian tissue, bacteria multiply and trigger an acute inflammatory response, characterized by vasodilation, increased vascular permeability, and recruitment of neutrophils and macrophages. The release of pro-inflammatory cytokines, such as tumor necrosis factor-alpha and interleukins, leads to local tissue damage and the formation of microabscesses. If the infection is not controlled, these microabscesses can coalesce to form a larger abscess cavity filled with necrotic debris and pus. The ovary's rich blood supply and its location within the ovarian bursa, which is a closed sac, can limit the spread of infection but also create a favorable environment for abscess formation. Chronic oophoritis may result in fibrosis, adhesions, and destruction of ovarian follicles, leading to impaired folliculogenesis and hormonal imbalances. In cases of autoimmune oophoritis, the immune system produces antibodies against ovarian antigens, leading to lymphocytic infiltration and gradual destruction of ovarian tissue. This can result in premature ovarian failure and infertility. The hormonal milieu, particularly high progesterone levels during diestrus, can suppress cell-mediated immunity and enhance bacterial growth, exacerbating the infection. Prostaglandins released during inflammation can also cause luteolysis and disrupt the estrous cycle.

Several intrinsic and extrinsic factors predispose animals to oophoritis and ovarian abscess. Intrinsic factors include age, with mature cycling females being more susceptible due to repeated exposure to reproductive hormones and potential uterine infections. Breed may play a role, with certain breeds having a higher incidence of reproductive disorders, such as pyometra, which can predispose to ovarian infection. Nulliparity is a risk factor because repeated estrous cycles without pregnancy can lead to endometrial hyperplasia and cystic changes, increasing the risk of ascending infections. Hormonal imbalances, such as hyperestrogenism or hyperprogesteronism, can alter the local immune environment and promote bacterial growth. Anatomical abnormalities, such as a persistent hymen or vaginal strictures, can impede drainage and facilitate ascending infections. Extrinsic factors include the use of exogenous progestins for estrus suppression or treatment of behavioral issues, which can increase the risk of uterine and ovarian infections. Poor hygiene during breeding, especially in kennels or catteries, can introduce bacteria into the reproductive tract. Iatrogenic factors, such as improper surgical technique during ovariohysterectomy, can lead to contamination and subsequent ovarian abscess. Trauma to the abdomen, such as from a road traffic accident, can cause ovarian damage and predispose to infection. Immunosuppression, whether due to concurrent disease, stress, or drug therapy, can increase susceptibility to infections. Additionally, the presence of ovarian neoplasms, such as granulosa cell tumors, can create a nidus for infection due to necrosis and compromised blood supply.

Clinical signs of oophoritis and ovarian abscess can be variable and often nonspecific. In acute cases, animals may present with fever, lethargy, anorexia, and abdominal pain. The pain may be localized to the affected ovary and can be elicited on abdominal palpation. Vomiting and diarrhea may occur if peritonitis develops. In chronic cases, signs may be more subtle, including weight loss, intermittent fever, and poor body condition. Reproductive signs may include vaginal discharge, which can be purulent or sanguineous, especially if there is concurrent metritis or pyometra. Affected animals may show signs of estrus abnormalities, such as prolonged or irregular estrous cycles, or may be infertile. In some cases, the condition is asymptomatic and only discovered incidentally during imaging or surgery. On physical examination, abdominal palpation may reveal an enlarged, painful ovary, but this is often difficult to detect, especially in obese animals. Rectal palpation in large dogs may allow palpation of the ovaries, but this is rarely performed. If the abscess ruptures, acute peritonitis can develop, leading to severe abdominal pain, shock, and potentially death. In queens, signs may be similar, but they may also exhibit behavioral changes such as increased vocalization or restlessness. It is important to note that these signs are not specific to oophoritis and can be seen in many other reproductive and non-reproductive conditions.

Differential diagnoses for oophoritis and ovarian abscess include: 1) Ovarian neoplasia, such as granulosa cell tumors, which can present with similar clinical signs and palpable masses; ultrasonography and histopathology are needed to differentiate. 2) Ovarian cysts, which are common in older animals and can cause hormonal imbalances but are usually not painful or associated with systemic signs. 3) Pyometra, which can cause vaginal discharge, fever, and abdominal pain, but the uterus is the primary site of infection; imaging can help differentiate. 4) Metritis, which is inflammation of the uterus, often postpartum, and can present with similar signs. 5) Peritonitis, which can be primary or secondary to other conditions, and may cause acute abdominal pain and fever. 6) Gastrointestinal disorders, such as pancreatitis or gastroenteritis, which can cause vomiting, anorexia, and abdominal pain. 7) Urinary tract infections or urolithiasis, which can cause abdominal pain and fever. 8) Foreign body or trauma, which can cause localized inflammation and abscess formation. 9) Autoimmune diseases, such as systemic lupus erythematosus, which can cause multisystemic signs. 10) Ectopic pregnancy or fetal death, which can cause reproductive signs and abdominal pain. Definitive diagnosis requires a combination of imaging, cytology, culture, and histopathology.

The diagnostic approach to suspected oophoritis or ovarian abscess should be systematic. 1) Clinical triage: Obtain a thorough history, including reproductive status, estrous cycle stage, recent breeding, and any prior reproductive issues. Perform a complete physical examination, including abdominal palpation and assessment of vital signs. 2) Laboratory tests: Complete blood count (CBC) and serum biochemistry profile to assess for leukocytosis, left shift, toxic neutrophils, and organ dysfunction. Serum progesterone and estrogen levels to determine the stage of the estrous cycle and assess ovarian function. 3) Vaginal cytology: Collect a vaginal swab to evaluate the stage of the estrous cycle and detect inflammatory cells or bacteria. 4) Imaging: Abdominal ultrasonography is the most valuable imaging modality. It can reveal ovarian enlargement, abscess formation (hypoechoic or anechoic areas with thick walls), and free fluid in the abdomen. Color Doppler can assess blood flow. Radiography may be useful to detect mineralized structures or masses, but is less sensitive. 5) Fine-needle aspiration: If an ovarian mass is identified, ultrasound-guided fine-needle aspiration can be performed for cytology and culture. This should be done cautiously to avoid rupture and contamination. 6) Culture and sensitivity: Aerobic and anaerobic bacterial culture of aspirated fluid or tissue is essential for guiding antimicrobial therapy. 7) Histopathology: If surgery is performed, histopathological examination of the affected ovary is the gold standard for diagnosis. 8) Additional tests: In cases of suspected autoimmune oophoritis, anti-ovarian antibody testing may be considered, but is not widely available. 9) Exploratory laparotomy: If imaging is inconclusive and the patient is unstable, exploratory surgery may be necessary for diagnosis and treatment.

Laboratory findings in oophoritis and ovarian abscess are often nonspecific but can support the diagnosis. On complete blood count, leukocytosis with a left shift (increased band neutrophils) is common, indicating an inflammatory response. Toxic neutrophils may be seen in severe infections. Anemia may be present if chronic inflammation or blood loss occurs. Serum biochemistry may reveal hyperglobulinemia due to chronic inflammation, and liver enzyme elevations (ALT, ALP) may occur if there is hepatic involvement or sepsis. Hypoalbuminemia can result from protein-losing enteropathy or malnutrition. In cases of peritonitis, electrolyte imbalances and acidosis may be present. Serum progesterone levels can be elevated if the corpus luteum is affected, or may be low if ovarian function is compromised. Estrogen levels may be abnormal if follicular cysts are present. Vaginal cytology can show inflammatory cells (neutrophils, macrophages) and bacteria, but this is not specific. Urinalysis may reveal proteinuria or bacteriuria if there is concurrent urinary tract infection. Blood cultures may be positive in septicemic cases. Culture of aspirated ovarian fluid or tissue is essential for identifying the causative organism and determining antimicrobial sensitivity. Histopathology of the ovary will show acute or chronic inflammation, with neutrophilic infiltration, necrosis, and abscess formation. Special stains, such as Gram stain, can help identify bacterial organisms.

Imaging plays a crucial role in the diagnosis of oophoritis and ovarian abscess. Abdominal ultrasonography is the preferred modality. In acute oophoritis, the ovary may appear enlarged, with a hypoechoic parenchyma and loss of normal follicular architecture. In chronic cases, the ovary may be small and hyperechoic due to fibrosis. An ovarian abscess appears as a well-defined, thick-walled, hypoechoic or anechoic structure within the ovary, often with internal echoes or debris. Color Doppler may show increased blood flow around the abscess. Free fluid in the abdominal cavity may be seen if there is rupture or peritonitis. Ultrasonography can also assess the uterus for concurrent pyometra or metritis. Radiography is less sensitive but may show a soft tissue mass in the ovarian region, and in chronic cases, mineralization of the abscess wall may be visible. Computed tomography (CT) and magnetic resonance imaging (MRI) provide more detailed anatomical information and can be useful in complex cases, but are not routinely available in veterinary practice. Vaginoscopy is not directly useful for ovarian evaluation but can assess the vagina and cervix for signs of infection. In pregnant animals, ultrasonography can also assess fetal viability and detect any ovarian abnormalities. It is important to note that imaging findings may be subtle, and a definitive diagnosis often requires histopathology.

Cytological and histopathological examination is essential for definitive diagnosis of oophoritis and ovarian abscess. Fine-needle aspiration of an ovarian mass can yield material for cytology. Cytological findings may include neutrophils, macrophages, and necrotic debris, and bacteria may be seen if the sample is stained with Gram stain. However, cytology cannot always distinguish between inflammation and neoplasia. Histopathology of the affected ovary is the gold standard. In acute oophoritis, the ovarian parenchyma is infiltrated with neutrophils, and there is edema and hyperemia. Microabscesses may be present. In chronic oophoritis, there is infiltration with lymphocytes, plasma cells, and macrophages, along with fibrosis and destruction of ovarian follicles. An ovarian abscess is characterized by a central cavity filled with pus, surrounded by a fibrous capsule. The surrounding ovarian tissue may show signs of inflammation and necrosis. Special stains, such as Gram stain, can help identify bacterial organisms. Immunohistochemistry may be used to identify specific pathogens or to differentiate between inflammatory and neoplastic conditions. In cases of autoimmune oophoritis, there is lymphocytic infiltration and destruction of ovarian follicles, and anti-ovarian antibodies may be detected in the serum. Histopathology is also important to rule out ovarian neoplasia, which can mimic oophoritis clinically and on imaging.

Treatment of oophoritis and ovarian abscess typically involves a combination of surgical and medical management. The definitive treatment is surgical removal of the affected ovary, either via ovariectomy or ovariohysterectomy. This is recommended to eliminate the source of infection and prevent complications such as peritonitis or sepsis. In cases where the animal is a valuable breeding animal and the infection is unilateral and mild, a conservative approach with antimicrobial therapy and supportive care may be attempted, but this is risky and not generally recommended due to the high likelihood of recurrence and the potential for rupture. Medical management includes antimicrobial therapy based on culture and sensitivity results. Broad-spectrum antibiotics should be initiated immediately, such as amoxicillin-clavulanate (12.5-25 mg/kg PO q8-12h) or cefazolin (22 mg/kg IV q8h), and then adjusted based on culture results. Anaerobic coverage is important, so metronidazole (10-15 mg/kg PO q12h) or clindamycin (11 mg/kg PO q12h) may be added. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) can be used to reduce inflammation and pain, but should be used with caution in dehydrated or hypotensive animals. Supportive care includes intravenous fluids to correct dehydration and electrolyte imbalances, and nutritional support if the animal is anorexic. In cases of peritonitis, aggressive fluid therapy and possibly abdominal lavage during surgery are necessary. Hormonal therapy is not indicated for the treatment of oophoritis or abscess, but may be used to manage the estrous cycle in breeding animals after recovery. The prognosis is generally good with early surgical intervention and appropriate antimicrobial therapy.

The prognosis for oophoritis and ovarian abscess is generally good if the condition is diagnosed early and treated aggressively with surgical removal of the affected ovary and appropriate antimicrobial therapy. Most animals recover without complications. However, the prognosis can be guarded to poor if the abscess ruptures, leading to peritonitis and sepsis, or if the infection is caused by a resistant organism. In cases of bilateral oophoritis or if both ovaries are affected, the animal will become infertile, which is a significant consideration for breeding animals. If only one ovary is affected and the other is healthy, fertility may be preserved, but there is a risk of recurrence. Chronic oophoritis can lead to fibrosis and loss of ovarian function, resulting in hormonal imbalances and infertility. The underlying cause also affects the prognosis; if the oophoritis is secondary to a systemic disease, such as FIP, the prognosis is poor. Negative prognostic indicators include severe systemic illness, peritonitis, septic shock, and delayed treatment. With prompt and appropriate treatment, the short-term survival rate is high, but long-term fertility may be compromised. Regular follow-up is recommended to monitor for recurrence and to assess reproductive function.

Follow-up care after treatment for oophoritis and ovarian abscess is important to ensure complete resolution and to monitor for complications. After surgical removal of the affected ovary, the animal should be monitored for signs of infection, such as fever, lethargy, or incisional discharge. The surgical site should be kept clean and dry, and the animal should be restricted from excessive activity for 10-14 days. Antibiotics should be continued for at least 7-10 days after surgery, or longer if there was significant infection. A recheck examination should be performed 7-14 days after surgery to assess healing and to review histopathology results. If the animal is a breeding animal, a reproductive evaluation should be performed after recovery, including vaginal cytology and hormone assays to assess the remaining ovary's function. Serial ultrasonography may be recommended to monitor the remaining ovary for any abnormalities. If the animal was treated medically without surgery, repeat ultrasonography should be performed 4-6 weeks after treatment to confirm resolution of the abscess. In cases of peritonitis, more intensive monitoring is required, including serial blood work and imaging. Long-term follow-up should include regular reproductive health checks, especially if the animal is used for breeding. Any recurrence of clinical signs should prompt immediate evaluation.

Clinical pearls: 1) Oophoritis and ovarian abscess are rare but should be considered in any intact female with fever, abdominal pain, and reproductive signs. 2) Ultrasonography is the most useful diagnostic tool; look for an enlarged ovary with a thick-walled, fluid-filled structure. 3) Culture and sensitivity are essential for guiding antimicrobial therapy; always collect samples during surgery or aspiration. 4) Surgical removal of the affected ovary is the treatment of choice; do not delay surgery if the animal is unstable. 5) In breeding animals, consider the value of the remaining ovary; if possible, perform a unilateral ovariectomy to preserve fertility. Pitfalls: 1) Do not rely solely on clinical signs; they are nonspecific and can be mistaken for other conditions. 2) Avoid fine-needle aspiration of an ovarian abscess without surgical backup, as it can cause rupture and peritonitis. 3) Do not use corticosteroids to reduce inflammation, as they can immunosuppress the animal and worsen the infection. 4) Do not delay surgery in favor of medical management alone, as this can lead to rupture and sepsis. 5) Be aware that ovarian abscesses can be associated with ovarian neoplasia; always submit tissue for histopathology.

Current drug protocols for oophoritis and ovarian abscess are primarily based on antimicrobial therapy and supportive care. Antibiotics should be chosen based on culture and sensitivity, but initial therapy should cover common pathogens, including gram-negative and anaerobic bacteria. Recommended protocols include: Amoxicillin-clavulanate (12.5-25 mg/kg PO q8-12h) for 7-14 days; Cefazolin (22 mg/kg IV q8h) for hospitalized patients; Metronidazole (10-15 mg/kg PO q12h) for anaerobic coverage; Clindamycin (11 mg/kg PO q12h) as an alternative for anaerobes; Enrofloxacin (5-10 mg/kg PO q24h) for gram-negative coverage, but use with caution in young animals due to cartilage effects. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as Carprofen (2.2 mg/kg PO q12h) or Meloxicam (0.1 mg/kg PO q24h) can be used for pain and inflammation, but should be avoided in animals with renal disease or dehydration. Supportive care includes intravenous fluids (e.g., Lactated Ringer's solution at 60-100 ml/kg/day) to maintain hydration and electrolyte balance. In cases of septic shock, vasopressors such as dopamine (5-10 mcg/kg/min IV) may be needed. Hormonal therapy is not indicated for the treatment of oophoritis or abscess, but in breeding animals, after recovery, the estrous cycle can be managed with protocols such as aglepristone (10 mg/kg SC on days 0, 1, and 2) for estrus induction or prostaglandins for luteolysis. However, these should only be used after complete resolution of the infection.

Evidence-based literature on oophoritis and ovarian abscess in small animals is limited, as these are rare conditions. Most information is derived from case reports and retrospective studies. A retrospective study of ovarian lesions in dogs found that oophoritis accounted for 2% of cases, and ovarian abscesses were even rarer. The study emphasized the importance of histopathology for definitive diagnosis. Another case series described ovarian abscesses in three dogs, all of which were successfully treated with ovariohysterectomy and antimicrobial therapy. The authors recommended surgical removal as the treatment of choice. In cats, oophoritis has been reported in association with feline infectious peritonitis (FIP), and the prognosis is poor. There are no controlled clinical trials on the medical management of oophoritis, but antimicrobial therapy is considered standard. The use of NSAIDs is supported by their anti-inflammatory properties, but caution is advised. Overall, the evidence suggests that early surgical intervention and appropriate antimicrobial therapy result in a good prognosis, while delayed treatment can lead to complications. More research is needed to establish standardized diagnostic and treatment protocols.