A Two-Hit Hypothesis of Congenital Spinal Stenosis: Etiology, Clinical Presentation, and Management

Abstract

Congenital spinal stenosis (CSS) refers to narrowing of the spinal canal during embryologic development, resulting from abnormalities in endochondral ossification that produce shortened pedicles and a diminished canal reserve. CSS uniquely predisposes patients to a proposed "two-hit hypothesis," whereby minimal baseline canal reserve constitutes the first hit, predisposing patients to clinically significant neurologic deficits in response to degenerative changes or minor trauma as the second hit, often presenting during the fourth to sixth decade, with fewer degenerative changes compared to those with degenerative stenosis. The cervical spine is the most common location for a narrowed canal, followed by the lumbar and thoracic spine. Congenital tandem spinal stenosis, with a radiographic prevalence of 10%-20%, presents a diagnostic challenge due to overlapping upper and lower motor neuron findings, and whole-spine magnetic resonance imaging should be considered in patients with non-localizing neurologic findings or combined features of myeloradiculopathy and neurogenic claudication. Canal dimensions are influenced by race, sex, heritable factors, and antenatal developmental variables. Surgical management depends on symptom severity, neurologic deficits, alignment, and number of involved levels, with patients with CSS at elevated risk of complications related to shortened pedicles and reduced canal dimensions, including screw breach, dural tears, and symptomatic adjacent segment disease. Preoperative computed tomography is recommended for pedicle screw planning, given the atypical anatomy of CSS. Emerging artificial intelligence applications demonstrate high accuracy in automated canal measurement and stenosis detection, with potential to improve risk stratification of asymptomatic patients.