The pathogenesis of Chiari 1 malformations has been explained in several different ways, but extensive evidence suggests a relationship between loss of volume within the posterior cranial fossa and Chiari 1 presentations. It is important to be able to differentiate Chiari 1.5 from Chiari 1 malformations as they have similar clinical presentations, but the latter have progressed further and are characterized by caudal herniations of the brain stem through the foramen magnum. Despite the similarities of presentation, Chiari 1.5 malformations have greater rates of complications following posterior decompression surgeries, which are typically performed to relieve ventral compression. An improved understanding of the odontoid synchondroses could lead to better understanding of Chiari malformations and lead to improved treatment of patients with these presentations. Here we present a rare case of an accessory odontoid synchondrosis in a patient with a Chiari 1.5 malformation and ventral compression.

The pathogenesis of Chiari 1 malformations has been explained in several different ways, but extensive evidence suggests a relationship between loss of volume within the posterior cranial fossa and Chiari 1 presentations. It is important to be able to differentiate Chiari 1.5 from Chiari 1 malformations as they have similar clinical presentations, but the latter have progressed further and are characterized by caudal herniations of the brain stem through the foramen magnum. Despite the similarities of presentation, Chiari 1.5 malformations have greater rates of complications following posterior decompression surgeries, which are typically performed to relieve ventral compression. An improved understanding of the odontoid synchondroses could lead to better understanding of Chiari malformations and lead to improved treatment of patients with these presentations. Here we present a rare case of an accessory odontoid synchondrosis in a patient with a Chiari 1.5 malformation and ventral compression.

Caudal regression syndrome (CRS) is a rare congenital variation. A high incidence of renal and genitourinary malformations has been observed in patients with CRS, with the most common being neurogenic bladder and renal agenesis.We report a rare case report documenting both CRS and a pelvic kidney found during a diagnostic magnetic resonance imaging. Although renal anatomy variants are found in patients with CRS, a pelvic kidney is normally not part of the constellation of findings in this malformation. As seen in our patient, a pelvic kidney should be considered in patients suspected of having CRS.

The straight sinus is a division of the dural venous sinuses, found beneath the splenium of the corpus callosum. At the internal occipital protuberance, it comes together with the superior sagittal sinus and transverse sinus to form the torcular Herophili. It functions as a major site of venous drainage for the cerebellum, inferior sagittal sinus, and vein of Galen. Many morphological variations have been reported involving the angulation, positioning, and number of straight sinuses present.Patients with Chiari II and III malformations have been observed to have a high incidence of anatomical variation with their dural venous sinuses, including vertically oriented straight sinuses. Additionally, there is a high rate of hydrocephalus in this patient population. Herein, we report a vertically oriented straight sinus in a child.