contiguous

The term 'contiguous' is frequently used to describe the pathway of spread for infections, malignancies, or inflammatory processes that extend directly from one anatomic structure to an adjacent one, as opposed to spreading via hematogenous, lymphatic, or distant metastatic routes. Classic board-relevant examples include: contiguous spread of osteomyelitis from an adjacent soft tissue infection or sinus infection (e.g., frontal sinusitis leading to osteomyelitis of the frontal bone, or diabetic foot ulcers leading to contiguous osteomyelitis); contiguous spread of Hodgkin lymphoma, which characteristically spreads in an orderly fashion to adjacent lymph node groups (unlike non-Hodgkin lymphoma, which spreads non-contiguously); direct extension of appendiceal abscesses to nearby structures; and spread of odontogenic infections to contiguous fascial spaces in the head and neck. Recognizing contiguous spread patterns is clinically important because it affects diagnostic imaging strategies (e.g., MRI to assess contiguous bone involvement in osteomyelitis), staging systems (e.g., Ann Arbor staging for Hodgkin lymphoma relies on contiguous nodal involvement), and treatment approaches (e.g., surgical debridement of contiguous necrotic tissue, antibiotic selection for polymicrobial contiguous spread infections like diabetic foot osteomyelitis). Distinguishing contiguous spread from hematogenous spread is a common exam concept, as hematogenous osteomyelitis (more common in children, often monomicrobial, e.g., Staphylococcus aureus in long bone metaphysis) differs clinically and microbiologically from contiguous-spread osteomyelitis (more common in adults, often polymicrobial, associated with trauma, surgery, or vascular insufficiency).