PET-CT Reveals Treatment Response and Suspected Hepatic Tumour Recurrence in a Dog

This patient underwent PET-CT imaging as part of restaging and treatment response assessment for a history of aggressive nasal adenocarcinoma and hepatocellular carcinoma.

Bobo previously underwent radiation therapy for an aggressive nasal adenocarcinoma in December 2025. He was subsequently diagnosed with hepatocellular carcinoma, which was surgically removed in May 2026; surgical margins were uncertain. A CT performed in April 2026 identified multiple pulmonary nodules suspicious for metastatic disease, and alternating doxorubicin and carboplatin chemotherapy was commenced. A follow-up CT was planned to assess the pulmonary response to chemotherapy.

PET-CT was performed to provide whole-body restaging, evaluate for metabolically active recurrent or metastatic disease, assess the hepatic surgical site, characterise the previously identified pulmonary nodules, and further evaluate the previously irradiated nasal tumour.

While conventional CT provides detailed information about anatomical changes and tumour size, it may not always determine whether an abnormality represents active neoplasia, treatment-related change or inflammation. PET-CT combines anatomical and metabolic imaging, allowing areas of increased glucose metabolism to be identified and assessed alongside their structural appearance.

In this case, PET-CT provided an opportunity to assess multiple disease sites simultaneously, including the liver, nasal cavity, thorax and regional lymph nodes, while also evaluating the response of previously identified pulmonary lesions during chemotherapy.

One of the most significant findings was a moderately FDG-avid hepatic mass measuring approximately 2.3 cm, located eccentrically along the liver adjacent to the previous right liver lobectomy site. The lesion was mildly hypoattenuating on post-contrast CT and demonstrated an SUVmax of 8.06. No other avid hepatic nodules or masses were identified, and the hepatic lymph nodes showed no increased FDG uptake.

Given the history of hepatocellular carcinoma and uncertain surgical margins, this finding was considered concerning for possible tumour recurrence or metastasis. However, hepatic abscessation could not be excluded, and ultrasound examination with aspiration was recommended for further characterisation.

Within the head and neck, a small region of contrast-enhancing soft tissue was identified adjacent to the roots of the maxillary canine and within the left nasal passages. This region demonstrated only minimal FDG uptake, with an SUVmax of 1.7, and extended caudally to the level of the second maxillary premolar. Turbinate lysis was present throughout the left nasal passages, with possible permeative lysis or thinning of the adjacent left maxillary bone.

The low metabolic activity of this soft tissue abnormality made interpretation less definitive. The findings were considered suspicious for either recurrence of the previously irradiated nasal tumour or inflammatory mucosal change associated with rhinitis. Comparison with previous imaging was recommended to determine whether the lesion had progressed.

Importantly, the previously identified pulmonary nodules were no longer visible on the current examination. The largest previously described right caudal lung nodule, measuring approximately 1.2 × 1.0 cm, was not identified on this PET-CT. This finding is consistent with a favourable response of the previously identified pulmonary disease to chemotherapy. However, several small ill-defined ground-glass opacities were present in the right middle lung lobe. These may represent focal atelectasis or emerging metastatic nodules, and continued monitoring with repeat thoracic CT was recommended.
No enlarged or abnormally FDG-avid lymph nodes were identified throughout the body, providing no PET-CT evidence of lymph node metastasis at the time of examination.

Additional findings included mild increased FDG uptake associated with the right C4-C5 nerve root, which may represent neuritis; chronic right elbow dysplasia with mild joint inflammation; mild osteoarthrosis affecting multiple joints; mild increased uptake associated with the left anal gland, potentially related to anal sacculitis; and mild increased avidity within the gluteal musculature, considered likely to represent myositis. An incidental pulmonary bulla was also identified.

This case demonstrates the value of PET-CT in a patient with multiple concurrent oncological concerns and an ongoing chemotherapy protocol.

Whole-body PET-CT demonstrated resolution of the previously identified large pulmonary nodule, providing important information regarding the response of the suspected metastatic disease to chemotherapy. At the same time, PET-CT identified a metabolically active hepatic lesion at the site of previous hepatocellular carcinoma surgery, highlighting an area requiring further investigation to differentiate possible tumour recurrence or metastasis from hepatic inflammation or abscessation.

The examination also demonstrated only minimal metabolic activity within the previously irradiated nasal region. This helped narrow the differential diagnosis to possible local tumour recurrence versus inflammatory mucosal change, with comparison to previous imaging recommended for further assessment.

Importantly, no evidence of metabolically active lymph node disease was identified, providing additional staging information that would not be available from assessment of an individual anatomical region alone.

This case highlights how PET-CT can provide comprehensive metabolic and anatomical information across multiple disease sites in a single examination, supporting treatment-response assessment, restaging and targeted investigation of indeterminate abnormalities.

We are currently accepting referrals. Pet owners can contact their vet directly and request a referral to Pet Theranostics.

PET-CT offers an advanced imaging modality that can provide valuable information about tumour activity, treatment response and potential metastatic disease. For pet owners, it can provide a more comprehensive understanding of their pet’s disease and help guide the next steps in clinical management.

We are currently accepting referrals. Pet owners can contact their vet directly and request a referral to Pet Theranostics.