Microcystic and Macrocystic Lymphatic Malformations: Distinct Genetics and Clinical Strategies

Objective(s): To review the classification, genetics, diagnosis, and management of lymphatic malformations (LMs), emphasizing the clinical and therapeutic differences between macrocystic and microcystic subtypes to guide targeted treatment and subtype-specific clinical trial design. Methods: Narrative review synthesizing current literature on LM epidemiology, pathophysiology, imaging, histopathology, and treatments, including sclerotherapy, surgery, laser therapy, and targeted agents. Results: LMs are driven mainly by postzygotic PIK3CA mutations activating the phosphoinositol-3-kinase/mammalian target of rapamycin (PI3K/mTOR) pathway. Macrocystic LMs (>2 cm cysts) present as compressible masses, respond well to sclerotherapy, and allow radiologic volume assessment. Microcystic LMs (<2 cm cysts) are infiltrative, often cutaneous, with risks of lymphorrhea and infection; they show poorer sclerotherapy response, limited procedural success, and rely on clinical rather than imaging endpoints. Subtypes require distinct trial designs: magnetic resonance imaging can be used to determine volume reduction for macrocystic, while clinician-rated symptom improvement is required for microcystic. Conclusion: Despite shared PI3K/mTOR pathway alterations, macrocystic and microcystic LMs differ substantially in clinical presentation, disease behavior, and therapeutic response. Sclerotherapy remains the first-line treatment for macrocystic lesions and is often associated with favorable outcomes. In contrast, there are currently no Food and Drug Administration-approved therapies for microcystic LMs, and both surgery and sclerotherapy are associated with high recurrence rates and suboptimal long-term control. Recognizing these fundamental phenotypic and therapeutic distinctions is critical to optimizing patient care and to designing rational, phenotype-specific clinical trials.