Dumbbell Lesions¶

Definition¶

A dumbbell (or hourglass) lesion is a spinal tumor that extends through the neural foramen, creating an intradural/intraspinal component connected to an extraspinal (paravertebral) component via a waist at the foramen. This morphology is most commonly seen with nerve sheath tumors (schwannoma and neurofibroma) but can occur with other tumors.

Etiology¶

Schwannoma — Most common cause of dumbbell lesions
Neurofibroma — Particularly plexiform neurofibromas in NF1
Meningioma — Rare dumbbell morphology
Malignant peripheral nerve sheath tumor — Consider in NF1 patients
Lymphoma, metastasis — Can extend through the foramen

Imaging Findings¶

MRI¶

Dumbbell morphology — Intradural mass connected to a paravertebral mass via a constricted portion at the neural foramen
Foraminal widening — Smooth expansion and remodeling of the neural foramen by the tumor
Signal characteristics — Follow the parent tumor (schwannoma: T2-bright, enhancing; neurofibroma: target sign)
Evaluate both the intraspinal and extraspinal components for extent

CT¶

Foraminal widening with smooth bony remodeling (slow-growing benign tumors cause smooth scalloping; aggressive tumors cause irregular destruction)
Paravertebral soft tissue mass
Calcification within the mass is uncommon for nerve sheath tumors

Eden Classification (for cervical dumbbell tumors)¶

Classifies the extent of the intradural, foraminal, and extraforaminal components to guide surgical approach.

Clinical Pearl

When you see a dumbbell-shaped mass extending through a neural foramen, the most likely diagnosis is a schwannoma. The key management question is the surgical approach — does the surgeon need an anterior, posterior, or combined approach? The Eden classification and cross-sectional imaging guide this decision. Always evaluate the contralateral side and other levels for additional tumors, particularly in NF1 and NF2.

Key Points¶

Dumbbell lesions extend through the neural foramen connecting intraspinal and paravertebral components
Schwannoma is the most common cause
Smooth foraminal widening indicates a slow-growing benign process
MRI defines the extent of both components for surgical planning
Multiple dumbbell lesions suggest NF1 or NF2

References¶

Spinal schwannoma — dumbbell appearance. Radiopaedia.org. Available from: https://radiopaedia.org/cases/spinal-schwannoma-dumbbell-appearance
Matsumoto Y, Endo M, Harimaya K, Hayashida M, Doi T, Iwamoto Y. Malignant peripheral nerve sheath tumors presenting as spinal dumbbell tumors: clinical outcomes and characteristic imaging features. Eur Spine J. 2015;24(10):2119-25. Available from: https://pubmed.ncbi.nlm.nih.gov/25015181/
Asazuma T, Toyama Y, Maruiwa H, Fujimura Y, Hirabayashi K. Surgical strategy for cervical dumbbell tumors based on a three-dimensional classification. Spine (Phila Pa 1976). 2004;29(1):E10-E14. Available from: https://pubmed.ncbi.nlm.nih.gov/14699292/
Jiang L, Lv Y, Liu XG, Ma QJ, Wei F, Dang GT, et al. Results of surgical treatment of cervical dumbbell tumors: surgical approach and development of an anatomic classification system. Spine (Phila Pa 1976). 2009;34(12):1307-14. Available from: https://pubmed.ncbi.nlm.nih.gov/19455006/
Kim TS, Kuh JH, Kim J, Yuh WT, Han J, Lee CH, et al. Spinal schwannoma classification based on the presumed origin with preoperative magnetic resonance images. Neurospine. 2024;21(3):890-902. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11456939/