What is the next diagnostic step for a patient with a bump in the mouth and a negative ultrasound, initially suspected to be a salivary gland stone (sialolithiasis)?

Next Diagnostic Step After Negative Ultrasound for Oral Bump

Order a contrast-enhanced CT or MRI of the neck to fully evaluate the mass, as ultrasound has significant limitations for assessing deep structures and determining the full extent of oral cavity lesions. 1

Why Ultrasound Failed and What to Do Next

Ultrasound is limited for evaluating:

• Deep tissue extension and involvement of the floor of mouth 1
• Perineural tumor spread 1
• Bone invasion of the mandible or palate 1
• Oropharyngeal and retropharyngeal structures 1

The negative ultrasound does not rule out pathology—it simply means the lesion may be deeper than ultrasound can adequately visualize. 2

Recommended Imaging Algorithm

First-Line Advanced Imaging: CT with IV Contrast

Order CT of the neck with IV contrast if you suspect: 1

• Bone involvement (mandible, palate, or adjacent structures)
• Need to evaluate for calcifications (stones can still be present despite negative ultrasound)
• Rapid assessment is needed
• The patient cannot tolerate MRI

CT advantages: 1

• Superior visualization of bone erosion or remodeling
• Better detection of focal calcifications (including stones that ultrasound may have missed)
• Faster acquisition time
• Can evaluate for necrotic or hypervascular lesions with contrast

Alternative: MRI with and without IV Contrast

Order MRI if you suspect: 1

• Soft tissue mass requiring detailed characterization
• Perineural invasion (numbness, facial weakness, or trismus present)
• Deep lobe salivary gland involvement
• Need to distinguish benign from malignant lesions

MRI advantages: 1

• Superior soft tissue contrast resolution
• Better delineation of mass contours and local invasion
• Can detect signal changes suggesting malignancy
• Preferred for sublingual and submandibular gland tumors

Critical Clinical Decision Points

If the patient has any of these features, proceed directly to tissue diagnosis after imaging: 1

• Facial numbness or weakness
• Trismus or fixation of the mass
• Palpable neck lymphadenopathy
• Age >40 years with unexplained mass
• Rapid growth or ulceration

Tissue Diagnosis Strategy

Once imaging defines the lesion, obtain tissue diagnosis: 1

• Fine-needle aspiration biopsy (FNAB) for accessible superficial lesions
• Core needle biopsy (CNB) if FNAB is nondiagnostic (CNB has 94% sensitivity, 98% specificity, and only 1.2% inadequate samples vs. 8% for FNAB) 1
• Image-guided biopsy using ultrasound or CT guidance for deeper lesions 1

Common Pitfalls to Avoid

Do not assume the lesion is benign based solely on negative ultrasound. 2 Ultrasound sensitivity is operator-dependent and limited by depth and anatomic location.

Do not repeat ultrasound. 2 If the first ultrasound was negative but clinical suspicion remains, cross-sectional imaging (CT or MRI) is required—not another ultrasound.

Do not delay imaging in patients with red flag features (cranial nerve symptoms, rapid growth, fixation, or age >40). 1

Special Consideration for Sialolithiasis

If you still strongly suspect a salivary stone despite negative ultrasound: 3

• Ultrasound can miss stones <2-3mm in size 4
• CT without contrast is superior for detecting small calcifications 1
• Consider CT sialography or MR sialography if duct obstruction is suspected but no stone is visualized 1