Health Guide: Abscess Figure 12

Abscess Figure 12

Figure 12: Multifocal abscesses in young rat
Case history and photos

History

Benny Simpson, a rat estimated at 8 months of age, was adopted from the humane society with 3 of his brothers. He had been at his new home for 3 weeks before presentation. His owner has vast experience with this species, and is very knowledgeable about their care and needs. He was bright, active, and very interested in his surroundings. Exact knowledge about his appetite, bowel movements, urination, ets, were not known as he shared a cage with his 3 brothers

Clinical Signs

He presented to our clinic with concerns of a fairly acutely bloated abdomen. His abdomen was distended, but not painful. He had a firm round mass in the caudal abdomen. He was not passing a lot of stool, and it was hard to assess his urinations as there were frequent small amounts. Other than that, he had a 3mm raised cutaneous mass on his back. X-ray showed a granular appearance of the abdominal contents, and very poor detail to the abdomen. The chest cavity was normal on X-ray. Ultrasound showed a 3.8cm circular mass. It was very homogenous and isoechoic to the liver parenchyma. This was not consistent with a fluid filled cavity (ie blocked bladder). The attempt at ultrasound examination was extremely limited as Benny was not sedated and seemed uncomfortable for positioning, thus only a few seconds of scanning was done. As the mass was interfering with his ability to defecate normally, and seemed to be compressing his abdominal organs somewhat, the decision was made to do an exploratory surgery the next day.

The next day, Benny was still bright, active, eating, but seemed somewhat more distended. He was anesthetized. While under anesthetic, another brief ultrasound check was done (we didn’t want him under anesthetic too long as the mass would potentially compress blood return). At that point we saw the same mass, now slightlly larger, but 2 other round masses were seen near it. A ventral midline incision was made. There were very small encapsulated growths incorporated into the linea alba, and there were adhesions of the omentum to the body wall (non-medically-there were very small abscesses in the central ligament that is opened in the abdomen, and the coating structures of the abdomen were stuck to the body wall). There were a chain of sperical massees from the midline body wall, 1.0 - 1.5cm encapsulated masses, also dozens of 3-4mm inclusions in the omentum, and around the bowel. In the mid-caudal abdomen, the 4.5cm discrete mass was present but it was adhesed to the body wall, and had bowel adhesed to it (see photos). The liver had 4 massees presented, incorporated into the parenchyma, involving >50% of the organ. The spleen had 2 growths, and each kidney was >70% of the parenchyma involved with the masses. Based on the extensiveness of the lesions (50-60 discrete growths), the progression of the condition even over 24 hours, and the fact that every major abdominal organ was involved, the condition was deemed inoperable.

Diagnosis

The working diagnosis was a previous septicemia (bacteria in the blood stream) seeding the abdominal cavity, vs a very unusual cancer spread.

Histopathology demonstrated that the masses were indeed encapsulated abscesses with degenerated neutrophils (white blood cells), debris and large bacteria colonies, surrounded by a thick fibrous tissue capsule. The bacteria colonies were filamentous, gram positive rods that with further testing did stain with acid fast stain. Microbiology grew a large population of beta-hemolytic streptococcus lancefield group G. The filamentous Gram-positive rods were observed as well, but did not grow in culture, even with extended incubation. The differentials for this bacteria were nocardia species (pathology was leaning towards this), or actinomyces. Based on the lack of soil exposure, and the inability of this bacteria to grow in the lab environment, the likely diagnosis of actinomyces was made (actinomyces is generally very difficult to isolate). This organism is normally present in the cheek of rats, and definitely could have caused a generalized septicemia.

Treatment

N/A

Outcome

Benny was euthanized while under anesthetic, and samples were taken for pathology and culture & sensitivity due to multiple siblings present.

Follow-up Discussion

There still remains unanswered questions in this case. The main one for me was how was Benny so bright and active, when about 30% of his body weight was abscess and infected tissue? Also, how was he physically able to grow these abscesses so rapidly? The abdominal swelling was noticed over a period of a couple of days at home, and we saw a noticeable change in 24 hours at our clinic. We will also not know when the initial septicemic episode occurred.