What is the likely diagnosis and recommended management for a painful, hard nodule on the bony portion of the posterior ear in an otherwise healthy adult?

Painful Hard Nodule at the Bony Part at the Back of Ear

The most likely diagnosis is a mastoid osteoma, a benign slow-growing bone tumor that should be managed with imaging confirmation followed by surgical excision if symptomatic or causing cosmetic concern. 1, 2

Most Likely Diagnosis

Mastoid osteoma is the primary consideration for a painful, hard nodule on the bony posterior ear (mastoid region). 1, 2 These are rare benign bone tumors with an incidence of only 0.1-1% of all benign skull tumors, but they are the most common cause of a solitary hard mastoid swelling. 2

Key Clinical Features to Assess

• Location specificity: Osteomas are typically solitary, pedunculated bony growths attached to the tympanosquamous or tympanomastoid suture line. 3
• Pain characteristics: While osteomas are often painless, pain can occur and may manifest as ipsilateral temporal headache. 4
• Progressive enlargement: These lesions grow slowly over years (typically 5+ years in reported cases). 5
• Cosmetic deformity: Visible external mass or auricular protrusion is common. 5

Critical Differential Diagnoses to Exclude

You must rule out malignancy before assuming benign disease. The differential includes:

• Osteosarcoma: Although rare in the temporal bone, this is the most important malignancy to exclude, particularly given the presence of pain. 5
• Osteoblastic metastasis: Must be considered in the differential diagnosis of any mastoid mass. 5
• Posterior auricular swelling from complicated otitis media: This can indicate subperiosteal abscess or mastoiditis requiring urgent treatment. 6

Mandatory Diagnostic Algorithm

Step 1: Initial Imaging

Obtain conventional radiographs in two planes as the absolute first imaging study. 6, 7 This should never be skipped, even when clinical suspicion for osteoma is high.

Step 2: Definitive Imaging

High-resolution CT (HRCT) of the temporal bone without IV contrast is the gold standard for diagnosis. 2, 5 CT will demonstrate:

• A wide-based lesion involving the temporal bone cortex 5
• The extent of mastoid air cell involvement 1
• Internal bone architecture (compact vs spongiotic) 5

MRI is not indicated for typical osteoma but should be considered if there is concern for malignancy or soft tissue involvement. 6

Management Algorithm

For Confirmed Osteoma:

Surgical excision is indicated when:

• The lesion is symptomatic (causing pain or headache) 4
• Cosmetic deformity is present 5
• The patient desires removal 2

Surgical Approach:

Complete excision through a postauricular approach is the standard technique. 1, 2 Key surgical principles include:

• Drill until normal cortical bone is reached to prevent recurrence 1
• Perform cortical mastoidectomy if the mastoid air cell system is involved 1
• The postauricular approach is preferred over transcanal for mastoid osteomas 3

Critical Pitfalls to Avoid

Do not assume benign disease based on clinical appearance alone. Pain in a bony mastoid lesion should heighten concern for malignancy, and histopathological confirmation is mandatory. 5

Do not perform biopsy before imaging. Complete the imaging workup first to guide surgical planning. 6

Do not use a transcanal approach for mastoid osteomas. Unlike external auditory canal osteomas, mastoid osteomas require a postauricular approach for complete removal. 1, 3

Ensure complete excision by drilling to normal cortical bone. Incomplete removal leads to recurrence. 1

When to Refer Urgently

Immediate referral to a bone sarcoma center is required if:

• Imaging shows aggressive features (cortical destruction, periosteal reaction, soft tissue mass) 6, 7
• The patient is under 40 years old with an aggressive-appearing lesion 8
• There is rapid growth or severe progressive pain 7, 9

In these scenarios, biopsy must only be performed at the referral center by the surgeon who will perform definitive resection. 6, 8, 9