New PostRadiotherapy Works—But Why Do French Bulldogs with Brain Tumors Still Relapse? New MRI Clues Uncovered

Possible involvement of cerebrospinal fluid drop metastasis in the survival of French bulldogs after radiotherapy for presumed glial brain tumors

Munekazu Nakaichi, Yuki Nemoto, Toshie Iseri, Harumichi Itoh, Hiroshi Sunahara, Takuya Itamoto, Kazuhito Itamoto, Kenji Tani

Background

French bulldogs are increasingly diagnosed with intracranial brain tumors, predominantly glial in origin and often presumed to be oligodendrogliomas. Radiotherapy is considered the most effective treatment modality for canine brain tumors and has shown good local tumor control in previous studies. However, survival outcomes in French bulldogs appear poorer than expected despite apparent radiosensitivity. This study aimed to evaluate the therapeutic effectiveness of radiotherapy in French bulldogs with presumed glial brain tumors and to investigate potential causes of unfavorable prognosis using follow-up magnetic resonance imaging (MRI).

Methods

This retrospective study reviewed medical records and MRI findings from 15 French bulldogs with presumed glial brain tumors treated with definitive-intent megavoltage radiotherapy between 2017 and 2022. Diagnosis was based on characteristic MRI features, with histopathological confirmation available in one case. Radiotherapy was delivered using intensity-modulated radiation therapy at a total dose of 42 Gy in 10 fractions. Follow-up included scheduled MRI examinations after treatment completion and additional imaging at clinical deterioration. Survival time was calculated from the start of radiotherapy to death.

Results

Eleven of the 15 dogs completed the planned radiotherapy protocol. In all completed cases, MRI demonstrated marked regression or complete disappearance of the primary brain tumor, accompanied by clinical improvement. Despite this, median survival time for dogs completing radiotherapy was 509 days, which was shorter than previously reported for canine brain tumors. Most dogs died due to recurrence of neurological signs. In recurrent cases, MRI revealed prominent leptomeningeal contrast enhancement extending from the brainstem to the cervical spinal cord, with some dogs also showing spinal cord lesions or obstructive hydrocephalus. These imaging features were consistent with cerebrospinal fluid (CSF) drop metastasis. Similar but less pronounced leptomeningeal changes were observed in dogs that died early during treatment.

Limitations

The study was limited by its retrospective design, small sample size, and single-institution setting. Most cases lacked histopathological confirmation of tumor type, and no postmortem examinations were performed, preventing definitive confirmation of CSF drop metastasis as the cause of death. Additionally, a low-field permanent-type MRI system was used, which may have limited detection of subtle lesions.

Conclusions

The findings indicate that presumed glial brain tumors in French bulldogs are radiosensitive, with effective local tumor control achieved through radiotherapy. However, CSF drop metastasis likely contributes to recurrence of neurological signs and shortened survival, even after successful regression of primary lesions. The study highlights the need to consider CSF dissemination during follow-up and suggests that additional or alternative treatment strategies may be required to improve long-term outcomes in this breed.

Disclaimer: The summary generated in this email was created by an AI large language model. Therefore errors may occur. Reading the article is the best way to understand the scholarly work. The figure presented here remains the property of the publisher or author and subject to the applicable copyright agreement. It is reproduced here as an educational work. If you have any questions or concerns about the work presented here, reply to this email.