Imaging of the intrinsic muscles of the hand - part I: high-resolution ultrasound and 3T MRI appearance of symptomatic anatomical variants.

The intrinsic muscles of the hand (IMH) include the thenar muscles, hypothenar muscles, lumbrical muscles, dorsal interosseous muscles (DIOM), and ventral interosseous muscles (VIOM). The thenar muscles consist of the abductor pollicis brevis (APB), opponens pollicis (OPP), flexor pollicis brevis (FPB), and adductor pollicis (ADP). The hypothenar muscles comprise the abductor digiti minimi (ADM), flexor digiti minimi (FDM), and opponens digiti minimi (ODM). Numerous anatomical variants of the IMH exist - including the accessory abductor digiti minimi (aADM), adductor hypothenar muscle, extensor digitorum brevis manus (EDBM), lumbrical muscle (LM) variants, and accessory flexor digitorum superficialis of the index finger. Although these variants are common, they can cause symptoms, especially in nerve compression syndromes such as carpal tunnel syndrome (CTS) from median nerve (MN) compression or Guyon's canal syndrome from ulnar nerve (UN) compression. Knowledge of these variants and their imaging characteristics facilitates understanding of related pathologies and contributes to improved therapeutic management. These muscle variants are diagnosed using high-resolution ultrasound (US) and magnetic resonance imaging (MRI).This review provides a comprehensive overview of the normal anatomy of the IMH, their anatomical variants, and their imaging features. High-resolution US is the primary modality for studying the IMH, while high-field 3T MRI offers excellent spatial resolution and contrast.Understanding the anatomy and anatomical variants of the IMH is essential for accurately assessing both normal and pathological conditions using US and MRI. · Variants of the intrinsic hand muscles can be reliably diagnosed by ultrasound and high-resolution MRI.. · Accessory abductor digiti minimi (aADM) may cause compression of the ulnar nerve within the Guyon's canal.. · Extensor digitorum brevis manus (EDBM) can mimic a dorsal pseudotumoral soft-tissue mass.. · Variants of the lumbrical muscles may compress the median nerve within the carpal tunnel.. · Accessory flexor digitorum superficialis indicis can simulate a tumor or cause carpal tunnel syndrome.. · Bouredoucen H, Boudabbous S, Poletti P et al. Imaging of the intrinsic muscles of the hand - part I: high-resolution ultrasound and 3T MRI appearance of symptomatic anatomical variants. Rofo 2025; DOI 10.1055/a-2761-4259.