What are the possible causes and treatments for a hard lump on my finger?

Hard Lump on Finger: Diagnostic Approach and Management

Start with plain radiographs as your first imaging study, followed by ultrasound for further characterization of soft tissue masses. 1, 2

Initial Clinical Assessment

When evaluating a hard lump on the finger, key clinical features to identify include:

• Location specificity: Determine if the mass is superficial/subcutaneous versus deep, and whether it's near joints, tendons, or nail bed 1
• Timing and trauma history: Note any preceding injury, as ganglion cysts can develop after wrist hyperextension trauma, and scar sarcoidosis can arise in pre-existing scars 3, 4
• Pain characteristics: Severe localized pain with cold sensitivity suggests glomus tumor, while painless masses are more consistent with ganglion cysts or lipomas 5, 6
• Associated symptoms: Check for triggering/catching (trigger finger), numbness (nerve compression), or nail plate discoloration (subungual glomus tumor) 7, 5

Diagnostic Imaging Algorithm

Step 1: Plain Radiographs (Always First)

Obtain standard radiographs initially to identify bone involvement, calcifications, fractures, or radio-opaque foreign bodies. 1, 2

• Radiographs can reveal enchondromas (the most common bone tumor of the hand), sesamoid bone abnormalities, or cortical changes 8, 7
• However, recognize that radiographs have limited sensitivity (54%) and specificity (68%) for soft tissue masses and may be unrewarding for small, deep-seated, or non-mineralized lesions 2, 1

Step 2: Ultrasound (Primary Triage Tool)

Use ultrasound as your next step after radiographs for characterizing the soft tissue mass. 1, 2

• Ultrasound demonstrates excellent diagnostic accuracy with 94.1% sensitivity and 99.7% specificity for superficial soft tissue masses 1, 2
• It can definitively identify benign lesions including simple cysts, ganglion cysts (the most common hand mass, accounting for 50-70% of all masses), lipomas, and vascular malformations 1, 6
• Ultrasound can confirm fluid content in suspected ganglion cysts and visualize tenosynovitis in trigger finger cases 1, 7
• Important caveat: Ultrasound is highly user-dependent and less accurate for deep masses in large anatomic areas 1, 2

Step 3: MRI (When Ultrasound is Inconclusive)

Proceed to MRI without IV contrast when ultrasound findings are atypical, uncertain, or when clinical concern persists despite benign-appearing ultrasound. 1, 2

• MRI is the preferred advanced imaging modality for deep soft tissue masses of the hand and provides the most accurate information for surgical planning 2, 9
• It can identify occult ganglion cysts, distinguish ganglia from synovitis, and detect nerve compression with associated soft tissue abnormalities 1, 9
• MRI may demonstrate diagnostic findings for specific benign conditions (lipomas, hemangiomas, nerve sheath tumors, glomus tumors) 1, 5
• IV contrast is rarely necessary for typical presentations and does not add significant diagnostic value 1, 9

Step 4: CT (Limited Role)

CT is not typically ordered for initial evaluation but may be appropriate when:

• Complex osseous anatomy needs evaluation 1, 2
• Precise characterization of mineralization patterns is required 1
• MRI is contraindicated or unavailable 9

Most Common Diagnoses

The differential diagnosis prioritized by frequency includes:

1. Ganglion cysts (50-70% of hand masses): Fluid-filled, often near joints, can cause carpal tunnel syndrome if located volarly 6, 4
2. Giant cell tumor of tendon sheath: Second most common, requires surgical excision with notable recurrence rates 6
3. Epidermoid inclusion cysts: Common after trauma, require surgical excision 6
4. Enchondromas: Most common bone tumor of the hand, visible on radiographs 8
5. Glomus tumors: Rare but characteristic severe pain, cold sensitivity, and subungual location 5

Critical Pitfalls to Avoid

• Do not assume all finger lumps are benign: Malignant conditions can mimic benign tumors, and any mass not clearly characterized as benign on ultrasound warrants further evaluation 8, 2
• Do not rely solely on radiographs: Their limited sensitivity for soft tissue masses means significant pathology can be missed 2
• Do not skip biopsy for uncertain diagnoses: Advanced imaging should be followed by biopsy before definitive treatment of tumors of unknown diagnosis 8
• Do not delay evaluation of rapidly growing masses: These require prompt biopsy to exclude malignancy or systemic disease like sarcoidosis 3

When to Refer for Biopsy

Obtain tissue diagnosis when:

• Imaging findings are indeterminate or discordant with clinical presentation 1
• The mass increases in size on follow-up 1
• Ultrasound or MRI features suggest possible malignancy 2
• Clinical suspicion remains high despite benign-appearing imaging 8