PET-CT reveals canine cancer recurrence

PET Theranostics was referred a canine patient with a history of a caudal nasal tumour, previously treated with stereotactic radiation therapy approximately eight months prior. The suspected diagnosis at that time was adenocarcinoma, with mild cribriform plate involvement noted on earlier imaging.

Post-treatment, the patient had responded well clinically. A follow-up CT scan conducted after a single seizure episode three months ago showed no clear evidence of disease progression, and the seizure activity was successfully managed with anti-epileptic medication. However, the referring veterinarian and the pet owner remained appropriately vigilant, particularly after the development of several new cutaneous nodules. Given this history, advanced functional imaging with PET-CT was recommended to assess for tumour recurrence, metastatic spread, and to characterise the newly identified lesions.

While conventional imaging modalities such as CT provide excellent anatomical detail, they may not always distinguish between post-treatment change and active disease. PET-CT, by contrast, enables the assessment of metabolic activity, offering increased sensitivity in detecting viable tumour tissue. In this case, the primary objective was to determine whether there was residual or recurrent neoplastic activity within the nasal cavity and to evaluate for any distant metastasis.

The patient underwent PET-CT imaging using the radiotracer F18-fluorodeoxyglucose (F18-FDG), administered intravenously at a dose of 200 MBq. After a 68-minute uptake period, PET acquisition was performed, followed by contrast-enhanced CT imaging.

Physiological tracer distribution was observed in expected regions, including the brain, salivary glands, abdominal organs, and urinary tract, providing confidence in scan quality and interpretation.

The PET-CT scan identified a contrast-enhancing soft tissue mass within the mid to caudal aspect of the left nasal cavity, extending to the level of the cribriform plate. This lesion demonstrated marked FDG avidity (SUVmax ~10), consistent with metabolically active tissue and highly suggestive of recurrent or residual neoplasia.

There was also evidence of focal cribriform plate lysis with minimal extension into the ventral cranial vault, specifically the region of the left olfactory lobe. Importantly, this invasion was associated with minimal mass effect and no displacement of midline intracranial structures, indicating relatively localised progression.

Crucially, the adjacent brain parenchyma demonstrated FDG uptake comparable to the contralateral side, with no areas of reduced attenuation. This finding reduced the likelihood of significant radiation-induced necrosis, although MRI was suggested for further evaluation if clinically indicated.

From a staging perspective, there was no evidence of regional lymph node involvement, with mandibular and retropharyngeal lymph nodes appearing normal and only minimally avid. Additionally, the thoracic cavity was clear, with no pulmonary nodules or intrathoracic lymphadenopathy detected, effectively ruling out metastatic spread to the lungs.

Evaluation of the abdomen and musculoskeletal system did not reveal any clinically significant abnormalities. An incidental splenic nodule was identified, most consistent with benign extramedullary haematopoiesis.

Of particular interest to the referring veterinarian and the pet owner were the newly identified subcutaneous nodules. PET-CT demonstrated a small cutaneous lesion along the left thoracic wall measuring approximately 6.3 mm, with very low FDG uptake (SUVmax 0.4). This level of metabolic activity is strongly suggestive of a benign process.

No additional metabolically active cutaneous or subcutaneous lesions were identified, providing reassurance that there was no evidence of disseminated cutaneous malignancy.

An additional focus of increased FDG uptake was noted in the left forepaw, between the second and third digits. In the absence of structural abnormalities on CT, this was considered most consistent with inflammatory change, such as pododermatitis, rather than neoplastic disease.