Overview and definition
The bone marrow cavity is a normal anatomical compartment, not a lesion. It is the honeycomb of cancellous (trabecular) bone whose interstices house marrow between the cortical plates of the maxilla and mandible.[1] Marrow may be red (haematopoietic) or yellow (fatty); in adults, jaw marrow is predominantly fatty, although haematopoietic foci can persist (notably in the ramus/condyle) or re-expand with haematopoietic demand.[1] The marrow stroma contains sinusoids, reticular connective tissue, adipocytes, and endosteal osteoblasts/osteoclasts involved in remodelling.[2] In the edentulous jaws, marrow and lamellar bone dominate tissue composition, with marrow proportionally greater in the maxilla than the mandible and especially rich in the anterior maxilla, whereas the anterior mandible is dense lamellar bone with sparse marrow.[3] These regional differences explain the variable trabecular pattern seen radiographically.
Radiographic findings
Recognition. Marrow spaces appear as the radiolucent intertrabecular areas framed by a trabecular meshwork; density varies by site, reflecting the maxilla's higher marrow and the mandible's denser lamellar bone.[3] On panoramic imaging, posterior and mandibular regions show more reproducible trabecular appearances than the anterior and maxillary regions.[4][5]
Normal variation and mimics. Prominent or sparse marrow spaces are a recognised normal variant and a well-known interpretive pitfall; familiarity with jaw marrow changes across age is essential to avoid overcalling pathology.[6] Focal osteoporotic bone marrow defect presents as an ill-defined radiolucency that blends into surrounding trabeculae and must be distinguished from true lesions.[6] A Stafne bone cavity (a lingual mandibular depression often containing normal tissue) lies below the inferior alveolar canal and should not be mistaken for an odontogenic process.[7][8]
Discriminators. CBCT more reliably resolves cortical continuity, expansion, thinning, and destruction than panoramic radiography, helping separate normal marrow from pathology.[5][9] Features that argue against normal marrow include cortical destruction, periosteal reaction, root resorption, widened periodontal ligament space with lamina dura loss, or marrow replacement—findings associated with osteomyelitis, osteonecrosis, or haematolymphoid malignancy.[10][11][12]
Management and prognosis
Normal marrow cavity requires no treatment and no follow-up; interpretation is one of recognition and reassurance.[6] Correlate any questioned area with clinical findings and prior images to confirm stability. Red flags warranting advanced imaging (CBCT, and MR/CT or referral where malignancy is considered) include ill-defined margins that progress, cortical erosion, expansion, periosteal reaction, paraesthesia, swelling, or marrow replacement.[5][10][11] Atypical radiolucencies should prompt biopsy or specialist referral rather than observation alone.[6]