==== Sphenoclival Synchondrosis ====

=== Definition ===
The sphenoclival synchondrosis is a cartilaginous joint between the sphenoid bone and the clivus (part of the occipital bone) at the skull base, present during development and typically undergoing endochondral ossification in late adolescence or early adulthood.

=== Anatomy ===

Located at the junction between:

Posterior body of the sphenoid bone

Upper clivus of the occipital bone

Forms part of the central skull base synchondroses, along with:

Intersphenoidal synchondrosis

Spheno-occipital synchondrosis

Adjacent to vital structures:

Basilar artery

Brainstem

Cavernous sinus

Cranial nerves III–VI

=== Development ===

Composed of hyaline cartilage during childhood

Normally ossifies between ages 12–18

May persist longer in certain individuals, especially in syndromic or dysplastic conditions

=== Clinical Relevance ===

==== 1. Skull Base Tumors ====

Common site of origin for:

Chondromas

Atypical cartilaginous tumors (ACTs) / Grade 1 chondrosarcomas

Chordomas (typically not cartilaginous but also arise in clival region)

Tumors may originate from persistent cartilage remnants

==== 2. Skull Base Surgery ====

Important landmark in endoscopic endonasal approaches (EEA)

Close proximity to critical neurovascular structures

Needs careful navigation during clival drilling

==== 3. Imaging Characteristics ====

MRI: May be visible as cartilaginous signal (T2 hyperintense) in younger patients

CT: Fusion or non-fusion of bones can be appreciated

Persistent synchondrosis can mimic pathology in certain settings

==== 4. Differential Diagnosis ====

Normal synchondrosis vs. cartilaginous tumor

Chondroid tumor vs. chordoma

Fibrous dysplasia, metastasis, or infection at clival region

=== Summary ===

Transient developmental joint at skull base

Clinically relevant in pediatric neuroradiology and skull base tumor surgery

Persistence may serve as a nidus for cartilage-origin tumors