What is the diagnosis and treatment for a large tender lump on the bottom of the foot, specifically in the arch area?

Diagnosis and Management of a Large Tender Lump in the Foot Arch

The most likely diagnosis is a plantar fibroma or ganglion cyst, and you should obtain imaging with ultrasound or MRI to confirm the diagnosis before proceeding with treatment. 1, 2

Initial Clinical Assessment

The differential diagnosis for a large tender lump in the plantar arch includes:

• Ganglion cysts (most common, representing 24% of foot masses) 1
• Plantar fibromas (tendon/ligament-related lesions, 16% of foot masses) 1
• Soft tissue tumors (benign or rarely malignant) 2, 3
• Deep-seated benign fibrous histiocytoma (rare but can present with pain) 4

Key clinical features to assess:

• Duration of symptoms: Chronic evolution over months to years suggests benign lesions like ganglion or fibroma 5, 2
• Pain characteristics: Throbbing or hyperalgesic pain may indicate glomus tumor or deep fibrous histiocytoma 5, 4
• Size and mobility: Most benign lesions are mobile and well-circumscribed 2
• Associated symptoms: Walking difficulty, restricted mobility, or paresthesias 1

Diagnostic Workup

Obtain imaging studies immediately—do not rely on clinical examination alone, as diagnostic accuracy for foot lumps is only 58%. 2

Imaging Protocol:

• Start with ultrasound: Cost-effective first-line imaging to characterize the mass and assess vascular features 1, 5
• MRI is definitive: Provides superior soft tissue characterization and should be obtained if ultrasound is inconclusive or surgical planning is needed 1, 5
• Plain radiographs: Only if bony involvement is suspected 1

Critical Pitfall to Avoid:

Never attempt surgical excision without proper imaging and referral to a specialist if there is any uncertainty about the diagnosis. Non-tumor center surgery is a predictor for developing metastasis in the rare event of sarcoma. 3 Although malignancy is rare (only 1 in 101 cases in one series), the consequences of missed sarcoma are catastrophic. 2, 3

Treatment Algorithm

For Confirmed Benign Lesions:

1. Ganglion cysts:

   • Observation if asymptomatic 2
   • Aspiration or surgical excision if symptomatic 1

2. Plantar fibromas:

   • Conservative management with padding and orthotics initially 2
   • Surgical excision if pain persists or interferes with ambulation 2

3. Other benign tumors (glomus tumor, fibrous histiocytoma):

   • Surgical excision is curative and provides pain relief 5, 4

Referral Criteria:

Refer immediately to a specialist tumor center if:

• Tumor size >5 cm 3
• Rapid growth 3
• Fixed or deep-seated mass 3
• Any suspicion of malignancy on imaging 3

Post-Excision Management:

• Always send tissue for histological confirmation—30 different histological types have been identified in foot lumps 2
• Clinical diagnosis alone is unreliable 2

Key Clinical Pearls

• Female patients are more commonly affected (73% in one series) 2
• Certain lesions occur in specific foot zones—location matters for differential diagnosis 2
• Painful masses with vascular features on imaging should raise suspicion for glomus tumor 5
• Early referral before any surgical intervention improves outcomes and prevents complications 3