A 7-year-old intact female Labrador Retriever was presented because of a 1 day history of vomiting, anorexia, mild polyuria/polydipsia and signs of fatigue. The owner had noticed some discharge from the vulva, as well as mucus and helminths in the feces. The dog had been in estrus 2 weeks before presentation but was not mated. The owner reported episodes of vomiting and weakness during the dog’s previous estrus cycles. On physical examination the dog was normothermic, had a swollen vulva with a sparse amount of yellow discharge and showed signs of pain on abdominal palpation. Hematology showed mild leukocytosis (18.96 × 109 cells/L, reference 5.05–16.76 × 109 cells/L). A serum chemistry panel identified mild metabolic hypochloremia and respiratory alkalosis and mildly elevated lactate. Left lateral and ventrodorsal abdominal radiographs were obtained. The lateral radiograph showed two gas-filled tubular structures, measuring up to 3.5 times the height of the body of the 5th lumbar vertebra. There was one gas-filled tubular structure in the central abdomen, dorsal and parallel to the descending colon, and one in the craniodorsal abdomen, just ventral to the caudal thoracic and cranial lumbar vertebrae. The ventrodorsal radiograph showed that the two gas-filled structures were parts of the same, slightly contracted, tubular structure. In the caudal and mid abdomen the tubular structure was medial to the descending colon and had a soft tissue/fluid opacity in this region. The tubular structure then turned to the right crossing the midline at the level of the two first lumbar vertebrae. The most cranial segment followed the right cranial abdominal/caudal thoracic wall to reach the most dorsal part of the right cranial abdomen. The difference in location of the intraluminal gas on the lateral and ventrodorsal radiograph was considered to be due to gravity as a result of positional changes of the dog. Thus, the tubular gas and fluid-filled structure could be followed almost the entire length of the abdomen, from the cranial aspect of the urinary bladder to the stomach. In the caudal abdomen on the lateral radiograph the uterine body was faintly visible between the descending colon and the urinary bladder, measuring approximately 1.3 cm in diameter, subjectively considered to be normal for the large size of the dog and the phase in the estrus cycle. Small intestines with normal diameter and content were seen in the mid-abdomen. Because of the position and the gas content in the structure, the main radiological suspicion was small intestinal ileus likely due to mechanical intra- or extraluminal obstruction, despite that no foreign body or mass could be seen. Following the radiographic examination, abdominal ultrasound was performed to confirm ileus and locate the suspected obstruction. In the left mid and caudal abdomen there were two thin-walled tubular structures whose content created a hyperechoic interface associated with reverberation and comet tail-artifacts, indicating gas content. One of these structures had the typical appearance of an intestinal wall, with alternating hypo- and hyperechoic layers, and in some parts the interface with the content created a dirty acoustic shadow. This structure was considered to represent the descending colon. A second structure had a similar thickness but homogenously hypoechoic wall, without visible layers. The interface between the wall and the luminal content was uneven and, in some parts, hyperechoic speckles were visible within the wall, creating a faint “comet-tail” artifact, suspected to be gas within the wall, consistent with emphysema of the wall or ulceration. Apart from the gas there was echogenic fluid in the lumen in the second structure, visible when the gas was moving. When tracing the second structure, it followed the path of the colon but was medial to the descending and ascending colon and caudal to the transverse colon. By use of several positional changes of the dog aiming to change the location of the intraluminal gas and any superimposition of other organs, the structure could be seen reaching the right ovary from the cranial aspect, while caudally it was connected to the uterine body, confirming that this was the right uterine horn. The maximum diameter of this right uterine horn was 3.3 cm. In order to make it possible to follow the left uterine horn, positional changes of the dog were required to move the right horn from its location in the left hemiabdomen. The left uterine horn was 0.9 cm in diameter, with mild amounts of intraluminal fluid and gas. The right medial iliac lymph node was mildly hypoechoic and rounded compared to the left one, with a thickness of 2 cm, interpreted as reactive lymphadenopathy. No free fluid nor free gas were found in the abdomen. The rest of the abdominal organs were normal. The radiological diagnosis was emphysematous pyometra, predominantly affecting the right uterine horn. The dog underwent surgery for ovariohysterectomy immediately after being treated with supporting intravenous Ringer-acetate solution (Fresenius AG, Bad Homburg, Germany) and methadone (Meda AB, Solna, Sweden). The ultrasonographic findings were confirmed on surgery. The right horn measured up to 5 cm in diameter and was thin-walled, distended and fluctuant due to the gaseous and liquid content. The left horn measured 1 cm in diameter and contained mainly fluid. When cutting through the uterine wall into the lumen gas and purulent exudate were found. Fluid samples for aerobic and anaerobic bacterial cultures were taken and Escherichia coli and beta-hemolytic streptococci were isolated. The uterus was not submitted for histopathology. The other abdominal organs were grossly unremarkable. The patient was treated with antibiotics in accordance to the result of the antibiogram and recovered fully in 2 weeks.