In a patient with a multilocular mandibular lesion on orthopantomogram, no scalloping between the roots, incisional biopsy reported a traumatic bone cyst, but aspiration yielded blood, what is the most likely diagnosis and appropriate next steps?

Diagnosis: Aneurysmal Bone Cyst (ABC)

The most likely diagnosis is an aneurysmal bone cyst, not a traumatic bone cyst, and you should proceed with advanced imaging (MRI without and with contrast) followed by definitive surgical management with curettage or resection.

Why This is ABC, Not Traumatic Bone Cyst

The clinical presentation strongly contradicts the biopsy report:

• Blood on aspiration is pathognomonic for ABC 1. Traumatic bone cysts (TBCs) are pseudocysts that typically contain minimal fluid or a small blood clot at most 2, 3
• Multilocular appearance is characteristic of ABC 1, while TBCs are almost always unilocular with scalloped borders 2, 3, 4
• The absence of root scalloping doesn't exclude ABC—this feature is variable and depends on lesion location and growth pattern

Critical Pitfall: Biopsy Sampling Error

Incisional biopsies of ABC can be misleading because:

• They may sample only fibrous septa or organizing hematoma
• The blood-filled sinusoidal spaces that define ABC may be missed
• The histologic overlap between organizing hematoma (in TBC) and ABC fibrous septa can confuse pathologists 1

Next Steps Algorithm

1. Immediate: Order MRI without and with IV contrast

• MRI is essential for definitive characterization of indeterminate or aggressive-appearing bone lesions 5
• Contrast enhancement is critical to distinguish primary ABC from secondary ABC (which can arise from other lesions) and to identify fluid-fluid levels pathognomonic for ABC 5
• MRI provides superior soft tissue characterization and assessment of cortical destruction 5

2. Consider CT without contrast as complementary

• CT better delineates cortical destruction and any mineralized matrix 5
• Useful for surgical planning, especially in multilocular lesions 5

3. Multidisciplinary Review

• Send imaging and biopsy slides to orthopedic oncology and specialized bone pathology
• The discordance between clinical/radiographic findings and histology mandates expert review

4. Definitive Treatment Planning

For confirmed ABC:

• Selective embolization should be considered pre-operatively for large, highly vascular lesions 1
• Surgical excision with curettage is the treatment of choice 1
• For large defects: immediate reconstruction with bone graft (iliac crest) 1
• ABCs are locally aggressive with potential for rapid growth—conservative observation is inappropriate 1

If TBC is confirmed on re-evaluation:

• Simple surgical exploration and curettage
• Allow cavity to fill with blood clot
• TBCs typically resolve spontaneously after minimal intervention 2, 4

Key Clinical Distinctions

Feature	ABC	TBC
Aspiration	Frank blood	Empty or minimal clot
Radiographic	Multilocular common	Unilocular typical
Growth	Rapid, aggressive	Slow/static
Treatment	Requires definitive surgery	Minimal intervention

Warning Signs for Aggressive Management

Watch for:

• Cortical expansion/destruction (suggests ABC over TBC)
• Rapid growth
• Symptomatic presentation (pain, swelling)
• Risk of pathological fracture

The presence of blood on aspiration in a multilocular lesion essentially rules out traumatic bone cyst 1, 2. Do not be falsely reassured by the biopsy report—proceed with advanced imaging and prepare for ABC management 5.