Complete surgical excision of a type V-variant dermoid sinus (V/VI overlap) associated with spina bifida in a Shiba Inu dog: A case report.

OBJECTIVE: To describe the clinical, imaging, surgical, and histopathologic features of a type V/VI overlap dermoid sinus (DS), and highlight diagnostic and therapeutic considerations. STUDY DESIGN: Case report. ANIMAL: A 16-month-old spayed female Shiba Inu dog. METHODS: The Shiba Inu initially presented at 4 months of age with a dorsal thoracic hair tuft. Radiography and ultrasonography suggested a DS; contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) were declined. The dog presented 12 months later for malodor, erythema, pruritus, focal pain on palpation, intermittent discomfort, and decreased appetite, although neurologic status remained normal. CT and MRI revealed spina bifida at T12 and a sinus tract extending from the skin to the dorsal dura mater, with mild dorsal displacement of the dura. Surgical excision via dorsal laminectomy and partial durectomy allowed en bloc removal of the tract and fibrous dural attachment. RESULTS: Histopathology confirmed a keratin-filled dermoid cyst lined by adnexal epithelium with pyogranulomatous inflammation and a fibrous dural connection, consistent with a type V/VI overlap DS. Recovery was uneventful, with no recurrence or neurologic deficits at the 12-month follow-up. CONCLUSION: Dural attachment may lead to clinical discomfort, even if neurological deficits are not present. Intraoperative assessment, histopathology, and advanced diagnostic imaging modalities such as CT and MRI are essential for surgical planning and accurate classification. CLINICAL SIGNIFICANCE/IMPACT: This is the first report of a Shiba Inu with a type V/VI overlap DS and thoracic spina bifida. Early surgical intervention based on an integrated approach can lead to a good long term patient outcome.