FRANCK FORTERRE, DVM, Diplomate ECVS 1 , DANIELA GORGAS, DVM, Diplomate ECVDI 1 , MARK DICKOMEIT, DVM 1 , ANDRE JAGGY, DVM, Diplomate ECVN 1 , JOHANN LANG, DVM, Diplomate ECVDI 1 * , and DAVID SPRENG, DVM, Diplomate ECVS & ACVECC 1 * 1 Small Animal Clinic, Divisions of Surgery, Radiology and Neurology, Vetsuisse Faculty, University of Berne, Berne, Switzerland. Vet Surg February 2010 39 2 165-172 ABSTRACT Objective—To investigate causes of the lack of clinical improvement after thoracolumbar disc surgery. Study Design—Case–control magnetic resonance imaging (MRI) study. Animals—Chondrodystrophic dogs with acute thoracolumbar disc disease treated by hemilaminectomy: 10 that had no short-term clinical improvement and 12 with "normal" clinical improvement. Methods—Dogs that had surgery for treatment of intervertebral disc extrusion (2003–2008) where thoracolumbar disc disease was confirmed by MRI were evaluated to identify dogs that had lack of clinical improvement after surgery. Ten dogs with delayed recovery or clinical deterioration were reexamined with MRI and compared with 12 dogs with normal recovery and MRI reexamination after 6 weeks (control group). Results—Of 173 dogs, 10 (5.8%) had clinical deterioration within 1–10 days after surgery. In 8 dogs, residual spinal cord compression was identified on MRI. Bleeding was present in 1 dog. In 3 dogs, the cause was an incorrect approach and insufficient disc material removal. In 3 dogs, recurrence occurred at the surgical site. In 1 dog, the centrally located extruded material was shifted to the contralateral side during surgery. These 8 dogs had repeat surgery and recovery was uneventful. In 2 dogs, deterioration could not be associated with a compressive disc lesion. Hemorrhagic myelomalacia was confirmed by pathologic examination in 1 dog. The other dog recovered after 6 months of conservative management. Conclusion—Delayed postsurgical recovery or deterioration is commonly associated with newly developed and/or remaining compressive disc lesion. Clinical Relevance—We recommend early MRI reexamination to assess the postsurgical spinal canal and cord, and to plan further therapeutic measures in chondrodystrophic dogs with delayed recovery after decompressive hemilaminectomy for thoracolumbar disc disease.