Effect of cranial tibial artery laceration on radiographic bone healing and perioperative complications in dogs undergoing tibial plateau leveling osteotomy.

During tibial plateau leveling osteotomy (TPLO), the laceration of the cranial tibial artery (LCTA) may occur, and the ligation of the cranial tibial artery might lead to impaired blood supply to the osteotomy site. The present case-control study aimed to evaluate the effect of LCTA on TPLO healing and the occurrence of perioperative complications. The incidence and predisposing factors to LCTA were also investigated. Fourteen cases experiencing LCTA were retrospectively enrolled from medical records of two veterinary teaching hospitals (LCTA group), whereas 28 randomly selected TPLOs that did not experience LCTA were included in the control group. Signalment data, proximal tibial epiphysis conformation, osteotomy features, perioperative complications, and bone healing were compared between the two groups. Bone healing was evaluated using the modified radiographic union scale for tibial fracture and the visual analog scale. The mean incidence was 9.6%. Bodyweight was significantly higher in the LCTA group compared to the control group (P = 0.009). Dogs belonging to the LCTA groups were significantly younger (P = 0.01). Intraoperative hypotension was significantly overreported in the LCTA group (P = 0.0001). None of the other variables differed significantly between the two groups. Dogs' size seems to be a predisposing factor, with dogs weighing >15 kg having 22 times more chance of experiencing LCTA. Due to the well-developed collateral blood supply of the canine hindlimb, LCTA and the closure of the cranial tibial artery did not appear to delay the radiographic bone healing or affect the incidence of perioperative complications.

Radiographic and CT features of metallosis in a lame dog after total hip replacement: the cloud sign.

A 2-year-old female American Akita was referred for CT of the pelvis and hindlimbs due to a left hindlimb lameness after a left total hip replacement. Referral radiographs and CT images demonstrated amorphous soft-tissue and mineral opacities surrounding the proximal femur and the prosthetic stem, consistent with the "cloud sign" reported as a characteristic of metallosis in humans. Dorsomedial displacement of the prosthetic head, multiple foci of geographic osteolysis alongside the "cloud sign", presumed pseudotumor lesions, and medial iliac lymphadenopathy were also identified with CT. Metallosis was confirmed based on ultrasound-guided cytology, revision surgery, and histopathology.

Osteochondrodysplasia and the c.1024G>T variant of TRPV4 gene in Scottish Fold cats: genetic and radiographic evaluation.

OBJECTIVES: The objectives of this study were to investigate the c.1024G>T SNP in the TRPV4 gene in Scottish Straight and Fold cats, and to evaluate the pattern of skeletal phenotype and the evolution of radiological signs of Scottish Fold osteochondrodysplasia (SFOCD) over time in heterozygous subjects. METHODS: DNA was obtained from blood samples of 17 cats (Scottish Fold: n = 12; Scottish Straight: n = 5) and subsequently genotyped by sequencing in a 249 bp region of the TRPV4 gene (exon 6), including the known c.1024G>T causative mutation for osteochondrodysplasia. Orthopaedic and radiographic analyses were performed on animals carrying the mutant allele. RESULTS: Genotyping by sequencing confirmed that all and only the Scottish Fold cats carried the mutant allele in a heterozygous asset. Furthermore, two other exon variants, already described in the literature as silent variants, were found in some of the sampled cats. Comparative orthogonal radiographic views of the shoulder, elbow, carpus, hip, stifle and tarsus were obtained. A mediolateral projection of the thoracic and lumbar column was also performed. Three out of four cats were clinically and radiographically examined again 1.5 years later. CONCLUSIONS AND RELEVANCE: Although the presence of the mutant allele in all the tested Scottish Fold cats was confirmed, only 1/12 showed clinical signs of SFOCD. Furthermore, no cats in the 1.5-year follow-up showed skeletal changes. Although significant, the c.1024G>T mutation in the TRPV4 gene, supposedly, is not the only cause or risk of developing SFOCD.

Computed tomographic appearance of transcaval ureter in two dogs and three cats: A novel CVC congenital malformation.

Transcaval ureter is a rarely reported human congenital malformation of the prerenal segment of the inferior vena cava (IVC) not yet reported in veterinary medicine. The objective of this multicenter retrospective case series study was to describe the computed tomography (CT) features of transcaval ureters in dogs and cats. Patients referring to pre- and post-contrast CT exams of the abdomen and presenting this abnormality were retrospectively included. Multiple qualitative features were described for each ureteral abnormality detected. Three cats and two dogs with transcaval ureter were identified consisting of a segmental duplication of the CVC at the prerenal level creating a vascular ring through which the ureter extended, identified as a double-barrel gun sign. The malformation was divided into two types according to the symmetry of the caval branches and location in relation to the aorta, namely, type I symmetrical branches and right-lateral to the aorta, and type II asymmetrically branches and right-dorsal to the aorta. In one case, the malformation was associated with hydroureter and mild pyelectasis. In three cases, the anomaly was incidental and, in the remaining two cases, the clinical significance was uncertain. This is the first study describing the presence of transcaval ureter in dogs and cats. CT was a suitable method for the diagnosis of transcaval and a focal double-barrel gun sign of the CVC is proposed as the hallmark feature of this anomaly. The clinical relevance of this congenital vascular malformation is unclear and needs to be further investigated.

Fall time may be a reliable discriminator between neoplastic and non-neoplastic urinary bladder lesions in dogs undergoing contrast-enhanced ultrasound: a pilot study.

Contrast-enhanced ultrasound (CEUS) can provide quantitative information on enhancement patterns and perfusion of lesions, based on time-intensity curves (TICs). No published studies have compared CEUS parameters in neoplastic and non-neoplastic urinary bladder lesions in dogs. The aim of the current prospective, pilot study was to quantitatively characterize the CEUS pattern of neoplastic and non-neoplastic urinary bladder lesions in dogs, assessing the influence of contrast arrival time (CAT) on the final appearance of the curves. Fourteen dogs with cyto-histopathological diagnoses were included (seven malignant and seven inflammatory lesions). B-mode ultrasound was performed followed by CEUS examination after an intravenous bolus injection of 0.04 mL/kg of contrast medium, and TICs were elaborated by dedicated software. Receiver operating characteristic curves (ROC) for each TIC parameter were obtained. Neoplastic lesions had subjectively shorter rise time (RT), time to peak (TTP) and fall time (FT) than inflammatory lesions. Based on ROC curve analyses, fall time ≥ 10.49 s was the most reliable parameter for diagnosing non-neoplastic disease in this small sample of dogs (area under the curve [AUC] 0.75, sensitivity 83.33%, specificity 66.67%). No difference was found between ROCs calculated for each parameter of TICs by adding or removing CAT. Results of the current study provide background for future, larger scale studies evaluating use of a CEUS FT threshold of 10.49 s as a possible discriminator for urinary bladder neoplastic lesions in dogs.

Safety of intravenous iodinated contrast medium injection in rabbits undergoing conscious computed tomography.

Background: Contrast media in CT is widely used in dogs and cats to provide superior tissue delineation and increase the diagnostic capabilities. These contrast-enhanced imaging techniques are gaining popularity in rabbits; published studies reporting the safety of doing so are lacking. Methods: This retrospective observational study aimed to determine the incidence of adverse events following the intravenous administration of iodinated non-ionic contrast medium in 350 rabbits. The medical records of this subset of rabbits admitted between January 2009 and November 2018, that underwent CT examination and received intravenous contrast media, were evaluated. Results: From the 350 rabbits, 342 rabbits were still alive 7 days after the scan. A total of eight rabbits died within 7 days of the scan, seven of which within the first 24 h. All deaths were presumed to be sequelae to the diseases they were being investigated for and not thought to be related to the administration of intravenous contrast medium. Conclusions: The results indicated that the use of intravenous non-iodinated contrast medium was well tolerated and safe in rabbits undergoing conscious CT examination.

Ultrasonographic and CT diagnosis of a complete splenic duplication with right splenic torsion and presumed regional splenic vein hypertension in a dog.

An 8-year-old mixed breed dog, was referred for lethargy, abdominal discomfort, hematemesis, and melena. Abdominal ultrasound revealed mineralization of the "right splenic vein" with collateral spiraling and a suspected splenic duplication. Computed tomography confirmed the duplication along with torsion of the splenic pedicle. Exploratory laparotomy confirmed the splenic torsion associated with congestion of the gastrointestinal vessels, indicative of a chronic onset of secondary regional splenic vein hypertension.

Preoperative planar lymphoscintigraphy allows for sentinel lymph node detection in 51 dogs improving staging accuracy: Feasibility and pitfalls.

Sentinel lymph node (SLN) mapping is the current gold standard for the oncological staging of solid malignancies in humans. This prospective observational study describes the feasibility and the limits of preoperative lymphoscintigraphy for SLN detection in dogs with spontaneous malignancies and the improvements in staging accuracy. Client-owned dogs with confirmed malignant neoplasia and absence of distant metastasis were prospectively enrolled. Lymphoscintigraphy was performed after the peritumoral injection of Technetium-99m labeled nanocolloids. Regional dynamic and static images were acquired, with and without masking of the injection site with a lead shield. The dogs were then subjected to surgery for tumor excision and SLN extirpation. Intraoperative SLN detection was performed by combining methylene blue dye and a dedicated gamma probe. Overall, 51 dogs with a total of 60 solid malignant tumors were enrolled. Lymphoscintigraphy identified at least one SLN in 57 of 60 cases (95%). The SLN did not always correspond to the regional lymph node (35/57, 61.4%). The use of a lead shield, masking the injection site, markedly improved the SLN visibility. The median time of SLN appearance was 11.4 ± 9.3 min. No side effects were observed. Preoperative lymphoscintigraphy allows for SLN detection in dogs and can improve staging accuracy by either identifying the SLN in a different lymphosome than clinically expected or discriminating the draining node in uncertain cases. The combined use of preoperative and intraoperative techniques is recommended to increase the SLN detection rate.

Prostatic leiomyosarcoma in a dog treated using a multimodal approach.

Prostatic leiomyosarcoma is an uncommon tumor encountered in male dogs, with only 2 cases reported in the veterinary literature with no follow-up described. A 12-year-old male intact German Wirehaired Pointer presented for evaluation of straining to defecate and urinate. Whole body computed tomography (CT) examination identified a spherical multicavitary expansile mass arising from the prostate gland and severely obliterating the pelvic canal. Partial subcapsular prostatectomy was performed, and histological and immunohistochemical results were consistent with prostatic leiomyosarcoma. Metronomic cyclophosphamide and nonsteroidal anti-inflammatory drugs were administered as adjuvant chemotherapy. Follow-up CT 10 months later indicated no signs of recurrence or metastasis. To the best of our knowledge, this patient represents the first report of successful multidisciplinary treatment consisting of partial subcapsular prostatectomy and adjuvant chemotherapy for prostatic leiomyosarcoma in a dog. After 15 months of follow-up, the patient remained recurrence-free without metastasis.

Four-dimensional CT excretory urography is an accurate technique for diagnosis of canine ureteral ectopia.

Computed tomographic (CT) excretory urography is commonly used to investigate canine ureteral ectopia (UE). Modern technology allows time-resolved CT imaging (four-dimensional CT excretory urography [4D-CTEU]) over a distance exceeding the detector collimation. Objectives of this prospective, observational, diagnostic accuracy study were to evaluate the diagnostic accuracy of CT excretory urography (CTEU) and 4D-CTEU for UE in dogs with lower urinary tract signs, assess the influence of pelvis positioning, and to determine the significance of the ureterovesical junction (UVJ) angle for UE diagnosis. Thirty-six dogs, with a total of 42 normotopic ureters, 27 intramural ectopic ureters, and three extramural ectopic ureters, underwent CTEU and 4D-CTEU with randomized pelvis positioning. Randomized CTEU and 4D-CTEU studies were scored by two observers for ureteral papilla location and murality on a grading scheme. Interobserver agreement, sensitivity, and specificity for ureter topia status and diagnosis were calculated. Computed tomographic excretory urography showed moderate interobserver agreement for the left ureter and perfect for the right ureter, whereas 4D-CTEU showed bilateral nearly perfect agreement between both observers. When comparing CTEU versus confirmed diagnosis, there was a sensitivity and specificity of 73% and 90.2%, respectively, whereas 4D-CTEU showed a sensitivity and specificity of 97% and 94.6%, respectively. An obtuse UVJ angle is significantly more commonly observed in ectopic intramural than normotopic ureters and is significantly associated with increased diagnostic confidence of UE. The use of a wedge to angle the pelvis did not increase the diagnostic confidence in determining ureteral opening position. Four-dimensional CT excretory urography is an accurate and reliable diagnostic technique to investigate UE as cause of urinary incontinence in dogs that is slightly superior to CTEU.

CT features of feline lipiduria and renal cortical lipid deposition.

OBJECTIVES: The aims of this study were to document the presence and prevalence of feline lipiduria and renal lipid deposition on CT, and to search for associations between the presence of lipiduria and sex, urinary tract abnormalities and urolithiasis. METHODS: The CT examinations of 252 cats were reviewed for the presence of an antigravitational hypodense bubble in the urinary bladder with density values between -180 Hounsfield units (HU) and -20 HU. To identify associations between lipiduria and sex, urinary tract abnormalities and urolithiasis, Fisher's exact test was used. Renal cortical density measurement was performed in all cats. The Mann-Whitney test was performed to compare renal cortical density between lipiduric and unaffected cats. RESULTS: A total of 27 domestic cats (10.7%) had CT evidence of lipiduria. Lipiduric cats had a significantly lower renal cortical density than unaffected cats (P <0.01). Male neutered cats had a significantly higher frequency of lipiduria and lower renal cortical density compared with female neutered cats (P <0.01). There was no significant difference between the groups regarding renal, ureteral or urethral abnormalities. CONCLUSIONS AND RELEVANCE: Lipiduria is a common physiological phenomenon in cats that can be detected on routine CT examinations. Decreased renal cortical density is associated with lipiduria. This may aid in the diagnosis of feline lipiduria and help to differentiate its presence from other pathological depositions and excretions.

Contrast-enhanced ultrasound for sentinel lymph node mapping in the routine staging of canine mast cell tumours: A feasibility study.

Canine mast cell tumours (MCTs) typically spread to lymph nodes (LNs) before reaching distant sites, and LN assessment is an important part of MCT staging. Sentinel LN (SLN) mapping techniques to identify draining LNs are being developed and could improve the accuracy of MCT staging. The primary objective of this feasibility study was to determine the safety and effectiveness of contrast-enhanced ultrasound (CEUS) to identify SLNs. Secondary objectives were to determine if the SLNs identified by CEUS coincided with the regional LN predicted by the anatomical lymphosomes, if previous MCT excision altered CEUS SLN findings, and if CEUS could identify MCT nodal metastases. Between June 2017 and March 2019, 59 dogs with 62 MCTs were enrolled. No adverse events related to CEUS were reported. CEUS detected at least 1 SLN in 59/62 MCTs (95.2%, 95% CI: 86.5-99.0%). In only 32/59 (54.2%) MCTs, clinicians would have correctly predicted the SLN(s) identified by CEUS. Among the 35 MCTs that had histological examination of the SLN(s), the prevalence of metastasis was 60% (95% CI: 42.1-76.1%). Additional staging procedures did not reveal any metastases in dogs with histologically non-metastatic SLNs. Integration of CEUS SLN mapping into the routine staging of MCTs is promising, but future studies are required to refine this procedure and to investigate if it would translate into a clinical benefit.

Effect of Stifle Flexion Angle on the Repeatability of Real-Time Elastosonography of the Patellar Ligament in Medium- to Large-Breed Dogs.

OBJECTIVE: The aims of this study were to describe the elastosonographic findings of the patellar ligament in healthy dogs >15 kg in different positions and determine the most appropriate stifle angle to perform elastosonography of the patellar ligament. STUDY DESIGN: Eighteen clinically healthy dogs, weighing >15 kg, were prospectively recruited. B-mode ultrasound and real-time elastosonography of both patellar ligaments were performed on days 0 and 14. Elastosonography examinations were performed with the stifle in four positions: standing position, lateral recumbency with the stifle positioned at 135 degrees extension and in full passive flexion and extension. RESULTS: The percentage hardness of the patellar ligament was significantly lower when the elastosonographic examination was performed with the dog standing, compared with the other positions (p < 0.005). The variability in the elastosonography readings for each stifle position was lowest when the dog was standing (89.32%). CONCLUSION: Elastosonography is a feasible technique for evaluating the elasticity of the normal canine patellar ligament in dogs >15 kg and would be a useful technique for investigating the mechanical changes within the patellar ligament following stifle surgery. Elastosonography of the patellar ligament should be performed with the dog standing to provide the most accurate elastosonograms with lowest variability between readings.

Use of contrast-enhanced ultrasound for the diagnosis of idiopathic renal hematuria in a dog.

Background: Idiopathic renal hematuria (IRH) generally occurs in healthy large-breed dogs that are <2-years-old. It is characterized by recurrent bleeding from the kidneys of unidentified cause. The final diagnosis is reached through the exclusion of primary urinary system and systemic causes of hematuria along with the direct visualization by cystoscopy of hematic urine jets at the ureteral orifice. Case Description: An 8-year-old female neutered Whippet was presented for investigation of a 4-week history of chronic intermittent macroscopic hematuria. Physical examination, systolic blood pressure, extensive laboratory workup (including coagulation profile and platelet count), urine culture, thoracic and abdominal radiographs, pneumocystogram, and double-contrast cystography were all unremarkable. B-mode ultrasound showed no abnormalities apart from a moderate amount of suspended echogenic amorphous material visible within the urinary bladder lumen. In the contrast-enhanced ultrasound (CEUS) study, a large amount of echogenic ill-defined material was noted projecting into the urinary bladder lumen from the right ureterovesical junction in the fundamental mode. This material was more conspicuous and markedly contrast-enhancing in the harmonic mode. Ultrasound contrast medium has the unique property to strictly remain within the vessels without interstitial trapping or elimination by the kidneys. Indeed, the presence of the micro-bubbles into the urinary tract lumen in the CEUS study was interpreted as a direct sign of active urinary tract bleeding. A diagnosis of IRH was reached through CEUS and B-mode ultrasound along with an extensive laboratory workup and periodic follow-up of the patient. No therapy was administered and at a 1-year follow-up, the patient was alive with no current episodes of macroscopic hematuria reported. Conclusion: To the authors' knowledge, this is the first report describing the use of CEUS for the characterization of IRH. CEUS could represent a safe, non-invasive, affordable novel alternative technique to cystoscopy or cystotomy for the real-time diagnosis of IRH.

Computed tomographic grading of middle ear disease in domestic rabbits (Oryctolagus cuniculi).

Ear disease, involving the middle and external ear, is commonly reported in pet rabbits, with lop-eared breeds predisposed. CT is the most reliable imaging modality for identifying otitis media (OM) in rabbits. This study aimed to develop a CT-based grading scale to classify the severity of CT changes in rabbits with presumed OM. Three observers independently reviewed CT images of 36 rabbits with OM. For both OM and material within the external ear canal, a grade of I to IV was used, (I=mild, IV=severe disease) and the level of agreement between reviewers was statistically evaluated. The study demonstrated that grades from the three reviewers showed a strong level of interobserver agreement. Comparisons between clinical signs and CT grade were also evaluated. Rabbits with grade IV OM had a high grade of material in the external ear canal. A high proportion of rabbits (83 per cent) underwent CT scanning conscious, demonstrating that diagnostic quality CT images are achievable without the need for anaesthetic intervention, minimising patient risk. This novel CT-based grading scale provides a methodology to correlate grade of disease with clinical signs, ear canal cytology, predisposing factors, treatment options and outcomes for rabbits with ear disease.

The effect of recumbency and hindlimb position on the lumbosacral interlaminar distance in dogs: a cadaveric computed tomography study.

OBJECTIVE: To examine the effect of sternal or lateral recumbency, with or without cranial extension of the hindlimbs, on the distance between the dorsal lumbosacral laminae in dogs. STUDY DESIGN: Blinded, randomized, crossover, experimental study. ANIMALS: A total of 19 canine cadavers. METHODS: Computed tomography of the lumbosacral junction was performed in four positions: sternal and right lateral recumbency, with hindlimbs extended cranially or not. Order of positioning was randomized. The lumbosacral interlaminar (LSI) distance, defined as the distance between the dorsal laminae of the seventh lumbar vertebra (caudal margin) and sacrum (cranial margin), was measured for each position by two independent assessors who were unaware of positioning. Mean distances in each position were compared using a paired t-test, corrected for multiple comparisons. RESULTS: For n = 19 cadavers [6 female; median (range) age 9 (0.3-16) years; weight, 20.4 (1.0-34.0) kg], cranial extension of the hindlimbs increased the LSI distance, compared with control, in both sternal (9.2 ± 2.2 mm versus 3.1 ± 1.3 mm, p < 0.001) and right lateral recumbency (8.2 ± 1.9 mm versus 4.9 ± 1.5 mm, p < 0.001). With the hindlimbs extended cranially, sternal recumbency increased LSI distance when compared with right lateral recumbency (p < 0.001). CONCLUSIONS AND CLINICAL RELEVANCE: Cranial extension of the hindlimbs in both sternal and lateral recumbency increases the LSI distance to an extent that is both statistically significant and of potential clinical relevance. Although ease of epidural access or injection was not assessed, the small (1 mm) difference in LSI distance between cranial hindlimb extension in sternal and right lateral recumbency is unlikely to be of clinical relevance. Conversely, cranial extension of the hindlimbs in either sternal or lateral recumbency would be expected to facilitate epidural injection.

Vascular conspicuity differs among injection protocols and scanner types for canine multiphasic abdominal computed tomographic angiography.

Multiphasic multidetector computed tomographic angiography is a standard diagnostic test for canine abdominal vascular disorders. Three imaging protocols have been previously described. The test-bolus protocol allows precise timing but can be time consuming to perform. Bolus-tracking software is fast and easy to use but can be problematic for exact timing of vascular phases. A recently described fixed-injection-duration protocol is not influenced by body weight and provides a wider temporal window for arterial acquisitions. Objectives of this retrospective and prospective, multicentric, method comparison study were to determine which of the three multidetector computed tomographic angiography protocols allows best vascular conspicuity of the canine abdomen and to assess the influence of different multidetector computed tomography (CT) scanners on study quality. Triple-phase multidetector computed tomographic angiography canine abdominal studies from 30 dogs were retrospectively retrieved from three different institutions. Each institution performed one of the three computed tomographic angiography protocols (4-row and 16-row multidetector CT). Prospectively, the three protocols were also acquired with similar conditions on a 64-row MDCT in 21 dogs. Main abdominal vessels were scored by blinded readers for each phase. The fixed-injection-duration protocol had the best combined arterial and portal vascular conspicuity on scanners of limited speed, while the test-bolus protocol provided the best overall vascular conspicuity on 64-row multidetector CT scanner. The quality of arterial studies performed on 64-row MDCT scanner was improved compared to the ones performed on four- to 16-row multidetector CT scanners. Findings supported the fixed-injection-duration protocol as the best compromise between an ideal portal vascular enhancement and an easily reproducible protocol on scanners with low and high number of detector rows.

Ultrasound and computed tomography of sacculitis and appendicitis in a rabbit.

A 9-month-old neutered male rabbit was referred for lethargy, anorexia, and gastrointestinal stasis. Routine hematology, serum biochemistry, and diagnostic imaging were performed. Computed tomography revealed a wall thickening of the sacculus rotundus and appendix, which was further confirmed on abdominal ultrasound. Full thickness biopsies were collected with histopathology diagnosing a chronic multifocal heterophilic granulomatous sacculitis and appendicitis. The patient was treated medically and at 6 weeks follow-up, clinical signs and intestinal changes had completely regressed. Inflammation of the sacculus rotundus and appendix should be considered as a cause of gastrointestinal stasis in rabbits.

Computed tomographic appearance of canine tonsillar neoplasia: 14 cases.

The palatine tonsil is an uncommon site of oral canine neoplasia. For affected tonsils, squamous cell carcinoma is the most frequent type of neoplasia, followed by melanoma and lymphoma. Computed tomography (CT) is increasingly used for investigation of canine oropharyngeal pathology; however, limited information is available on the CT appearance of tonsillar neoplasms. Objectives of this retrospective descriptive case series were to characterize the CT features of canine tonsillar neoplasia and determine whether specific CT features differentiate nonneoplastic from neoplastic tonsils. Computed tomographic studies of 14 dogs diagnosed with tonsillar neoplasia were retrieved from two referral hospitals and reviewed by two observers. Diagnosis was based on histology or cytology. Carcinoma was diagnosed in 11 dogs, melanoma in two and lymphoma in one dog. Specific CT features of the tonsil and regional lymph nodes did not differentiate neoplastic from nonneoplastic tonsillar diseases, but regional lymph node CT features were useful for diagnosis in some cases. Marked enlargement (width ≥ 18 mm, 12/18), heterogeneity (16/18), and loss of the hypoattenuating hilus (18/18) of the medial retropharyngeal lymph node were common concomitant features of tonsillar neoplasia. The medial retropharyngeal and mandibular lymphadenomegaly was ipsilateral to the neoplastic tonsil in 8/12 and 6/9 dogs, respectively. Five dogs demonstrated little or no enlargement of the tonsil despite the associated metastatic lymphadenomegaly. Tonsillar neoplasia should therefore be considered as a differential diagnosis for dogs with CT evidence of isolated medial retropharyngeal lymphadenomegaly (regardless of normally sized tonsils), or of any enlarged tonsil with no associated lymphadenomegaly.