A 3-month-old male intact domestic shorthair cat weighing 0.62 kg presented to the Texas A&M University Small Animal Teaching Hospital for evaluation of a large cervical swelling. The kitten first presented to the referring veterinarian for an examination prior to being adopted. At that time, the kitten was dehydrated and subcutaneous fluids were administered. During subcutaneous fluid administration, the kitten moved unexpectedly and the needle entered the ventral aspect of the left side of the neck. A swelling was immediately noted, the needle was removed and manual compression over the puncture site was applied until the swelling remained static in size. No significant bleeding was noted at the site of the puncture. The kitten was discharged to the owner’s care. The swelling increased over the next 48 h and the kitten was taken to a different specialty hospital for assessment. The veterinarian performed a fine-needle aspiration of the swelling and frank blood was withdrawn. Following the aspirate, the kitten exhibited signs of hypovolemic shock and a blood transfusion was administered. The kitten was subsequently referred to our institution approximately 24 h later. On physical examination the kitten was bright, alert and responsive. A large swelling was present on the left side of the neck and was approximately 4 cm in diameter (). On palpation, the swelling was immobile and firm with focal softer areas. Bloodwork was performed, including a coagulation panel, complete blood count (CBC) and serum chemistry profile. Coagulation parameters were within the normal range (prothrombin time 17 s, reference interval [RI] 13–22; partial thromboplastin time 69 s [RI 60–115]). On CBC, a moderate regenerative anemia was present (hematocrit 18% [RI 24–45] with 296,000 reticulocytes). Platelets were clumped but appeared adequate on blood smear, no blood parasites were seen and a saline agglutination test was negative. No abnormalities of concern were found on serum chemistry profile. The kitten was sedated with butorphanol (0.3 mg/kg IM), midazolam (0.2 mg/kg IM) and alfaxalone (1.0 mg/kg IM). An intravenous (IV) catheter was placed and alfaxalone 3.0 mg/kg given IV to effect for induction. The kitten was then placed under general anesthesia with sevoflurane. CT angiography of the head and neck was performed. An approximately 4 cm, fluid-to-soft tissue-attenuating, contrast-enhancing mass was noted on the left ventrolateral head and cervical region, extending from the level of the globe to the level of C2 ( and ). Progressive contrast filling within the mass was noted on sequential delayed phase sequences, with a small communication with the left common carotid artery, consistent with active hemorrhage. There was poor contrast enhancement of the left common carotid artery and its tributaries, compared with the right side, which was presumed to be secondary to compression from the mass effect and/or related to reduced volume owing to leakage of contrast into the pseudoaneurysm. A focus of fluid attenuation with rim contrast enhancement noted ventral to the left mandible was suspected to represent additional hemorrhage, hematoma or a communicating compartment of the larger mass. Surgical correction was recommended given concerns for active hemorrhage and continued growth of the structure. One day following CT, the kitten was anesthetized with buprenorphine (0.02 mg/kg IV), alfaxalone (3.0 µg/kg IV), midazolam (0.16 mg/kg IV) and ketamine (3.0 mg/kg IV). General anesthesia was initiated and maintained with sevoflurane. The left jugular vein was ligated with a vessel sealing device (Ligasure Small Jaw; Medtronic) to allow for better dissection and exploration of the cervical region. The left carotid artery was identified proximal to the swelling and 3-0 silk placed around it. Temporary occlusion did not yield any changes in anesthetic parameters; therefore, it was ligated proximal (caudal) to the pseudoaneurysm. The pseudoaneurysm capsule was first identified. It was pale pink in color, matching the surrounding tissue, and approximately 3 × 4 cm in size. The pseudoaneurysm was then catheterized with a 22 G over-the-needle catheter attached to a syringe and three-way stopcock device. Approximately 60 ml (96.8 ml/kg) blood was aspirated from the swelling, resulting in decompression of the swelling. A blood transfusion was elected due to the significant amount of blood removed and kitten’s small size. The anesthesia team administered two autotransfusions. The first was 10 ml blood mixed with 1 ml citrate phosphate adenine anticoagulant (CPDA) over 1 min. Since the kitten handled the first transfusion well, a second transfusion of 40 ml blood mixed with 4 ml CPDA was given over 4 mins. The pseudoaneurysm was noted to refill to its original size within minutes. An incision was created within the pseudoaneurysm, the capsule was explored and a large hematoma removed. Blood was collected with a needle and syringe from the pseudoaneurysm as it reappeared. The medial portion of the pseudoaneurysm continued to hemorrhage and the kitten began to decompensate. Blood was collected to measure the intraoperative packed red blood cell (pRBC) volume, which was 10%. A second autotransfusion of 50 ml blood with 5 ml CPDA was immediately given as a bolus. An allogeneic pRBC transfusion (30 ml total, 48.4 ml/kg) was started after the second autotransfusion over 5 mins. On the medial side of the pseudoaneurysm, an approximately 1 mm opening (lumen) was recognized to be the source of hemorrhage. Two 5-0 Prolene mattress sutures were placed. Hemostasis was confirmed. The remaining capsule and blood clot remnants were excised and submitted for histopathology. Aerobic and anaerobic cultures were taken at the time of wound closure and yielded no growth. The subcutaneous tissue and skin were closed routinely with 4-0 monocryl and 3-0 nylon, and a light bandage was placed around the neck. Total surgery time was 104 mins. The endotracheal tube was suctioned prior to extubation and a small mucous plug was removed. The kitten was recovered in an oxygen chamber at 40% but was able to be placed in room air within 24 h. The pRBC transfusion was completed in recovery and no additional blood products were required. The kitten was maintained on buprenorphine 0.018 mg/kg transmucosally every 8–12 h for 3 days and cefazolin (22 mg/kg IV q8h for 24 h) until it was switched to oral cephalexin (25 mg/kg PO q12h). In recovery, an abbreviated blood panel was performed and found to be unremarkable aside from a hematocrit of 25%. Postoperatively, the kitten had a head tilt and left sided Horner’s syndrome (). Histologically, approximately 90% of the submitted tissue was necrotic with numerous erythrocytes and a mixed inflammatory cell population dissecting the necrotic tissue. The remaining tissue was entirely composed of fibrosis. Attached to the necrotic tissue multifocally was a large amount of fibrin mixed with inflammatory cells, consistent with a thrombus. Given the degree of necrosis, pseudoaneurysm was deemed most likely but a true aneurysm could not be ruled out (). The kitten was hospitalized for 7 days postoperatively before going home due to the requirement of a rabies quarantine after it bit a staff member. The kitten continued to recover uneventfully at home. A 7-day course of cephalexin (25 mg/kg PO q12h) was administered while cultures were pending. Buprenorphine was discontinued after 3 days when the kitten no longer seemed painful. Three months postoperatively, the kitten had grown significantly in size and had no reoccurrence of clinical signs or swelling. The head tilt had fully resolved and Horner’s syndrome had partially resolved.