A circular depression at the spinoglenoid notch of a prehistoric Andean scapula: Plausible evidence of suprascapular nerve entrapment by a paralabral cyst.

While intraosseous cysts have been described in the paleopathological literature, it is rare to find reports concerning effects of soft tissue cysts, although they are relatively common in clinical contexts. Here we present plausible evidence of an extraosseous paralabral cyst, seen in an adult scapula from a Late Intermediate period commingled tomb (ca. AD 1200) at the northern highland site of Marcajirca, Ancash, Peru. The scapula demonstrated a smooth-sided concave depression at the spinoglenoid notch. The depression was notable for its regular appearance, with no bone deposition or destruction. Rather than reflect an intraosseous pathology, the defect likely resulted from pressure erosion from a space-occupying mass. A narrow strip of flattened bone connected the depression to the posterior-superior aspect of the glenoid. The location and morphology of the depression and its connection with the glenoid are consistent with the effects of a paralabral cyst that arose secondary to a tear of the posterior-superior glenoid labrum. A labral tear may act as a one-way valve permitting fluid to flow along a path of least resistance, often to the spinoglenoid notch. A cyst at the spinoglenoid notch would compress the suprascapular nerve, causing weakened function of infraspinatus and its eventual atrophy.