The calf clot of the lungs: Detection, overdiagnosis, and structured surveillance in isolated subsegmental pulmonary embolism.

Multidetector CT pulmonary angiography has increased detection of pulmonary embolism at the subsegmental level without a corresponding fall in overall PE mortality, placing isolated subsegmental pulmonary embolism (iSSPE) at the center of a management conflict: the 2021 CHEST guideline permits structured surveillance in selected patients, whereas the 2026 multisociety guideline recommends anticoagulation for all acute pulmonary embolism. We review iSSPE definition, diagnostic reliability, natural history, treatment-versus-surveillance outcomes, and guideline divergence. Across mixed cohorts, anticoagulation has not clearly reduced recurrence or mortality but increases bleeding; cancer-associated thrombosis is the clearest exception however. We propose a four-gate framework to guide surveillance versus anticoagulation.