Persistent fontanelles in Chihuahuas. Part I. Distribution and clinical relevance

Background: The Chihuahua dog breed is known for frequent occurrence of a bregmatic fontanelle on the dorsal skull. A common conception is that this skull defect is a clinically irrelevant finding. No studies, however, describe its prevalence or whether it is accompanied by other persistent fontanelles (PFs). Although Chihuahuas are predisposed to Chiari-like malformation (CM) and syringomyelia (SM), it is unknown whether PFs occur more commonly in dogs with clinical signs that are caused by CM or SM.

Hypothesis/objectives: To describe the number and location of PFs at cranial sutures (CSs) and to compare the occurrence of these PFs in dogs with and without CM/SM-related clinical signs. We hypothesized that PFs also occur commonly at lateral and caudal cranial surfaces, affect a higher number of CSs, and are larger in dogs with CM/SM-related clinical signs.

Animals: Fifty client-owned Chihuahuas with or without CM/SM-related clinical signs.

Results: Of the 50 dogs evaluated, 46 (92%) had either 1 or several PFs. The mean ± SD number of PFs was 2.8 ± 3.0 (range, 0-13). A total of 138 PFs occupied 118 CSs with 57 (48%) located dorsally, 44 (37%) caudally, and 17 (14%) laterally. The number of CSs affected by PFs was significantly higher (P ≤ .001) and total PF area was significantly larger (P = .003) in dogs with CM/SM-related clinical signs.

Conclusions and clinical importance: Persistent fontanelles are very common in this group of Chihuahuas and appear at dorsal, lateral, and caudal cranial surfaces. They are more numerous and larger in Chihuahuas with CM/SM-related clinical signs.