Proliferative periostitis

Proliferative periostitis is a form of chronic osteomyelitis characterized by reactive subperiosteal new bone formation in response to a low-grade inflammatory or infectious stimulus.[1][2] The condition is benign and self-limiting when the inciting cause is addressed. It overwhelmingly involves the mandible, where odontogenic infection—most often periapical pathology of a mandibular molar—stimulates the periosteum to deposit successive layers of new bone on the outer cortical surface.[3][4] The signature radiographic finding is a lamellated ("onion-skin") pattern of periosteal new bone superimposed on an intact or minimally altered cortex.[1][4] Management centers on eliminating the source of infection, after which the periosteal bone typically remodels toward normal contour.[2][3]

• Proliferative periostitis is the currently preferred descriptive term in the oral and maxillofacial pathology literature.[1][2]
• Periostitis ossificans is a widely used synonym, particularly in the European and Asian literature.[3][4]
• Garré osteomyelitis (also spelled Garré's osteomyelitis) remains the most recognized eponymous designation. Carl Garré originally described a sclerosing osteomyelitis of long bones in 1893; the term was later applied to the jaw entity, though the two conditions differ in pathogenesis and imaging appearance. Some authors discourage the eponym because of this historical imprecision.[2][3][5]
• Chronic osteomyelitis with proliferative periostitis is used when the emphasis is on the underlying osteomyelitis rather than the periosteal reaction alone.[1][2]
• The entity should be distinguished from diffuse sclerosing osteomyelitis, which produces widespread medullary sclerosis and may involve the condyle and masticatory muscles, and from chronic suppurative osteomyelitis, which features sequestra and fistulae.[6][7]

• Age: Predominantly affects children and adolescents, with most reported cases occurring between ages 5 and 15 years. The active osteogenic potential of the periosteum in young patients is thought to account for this predilection.[2][4][8]
• Sex: No consistent sex predilection has been established in published case series.[1][2]
• Site: The mandible is involved in the vast majority of cases, with the posterior body and angle region—adjacent to the first and second permanent molars—being the characteristic location. Maxillary involvement is rare. Occasional cases without an identifiable odontogenic source have been reported, raising the possibility of an immunologically mediated mechanism overlapping with chronic nonbacterial osteomyelitis.[1][3][4][8]

Presentation and symptoms

• The hallmark presentation is a unilateral, firm, non-tender or mildly tender bony swelling of the mandible, typically over the buccal aspect of the posterior body.[1][4]
• Onset is usually insidious, developing over weeks to months. Pain, when present, is generally mild and intermittent.[1][2]
• Overlying skin and mucosa are typically normal in color and temperature; erythema and warmth are uncommon unless acute exacerbation occurs.[4]

Examination findings

• Palpation reveals a hard, non-fluctuant expansion of the buccal cortex that is continuous with the underlying mandible.[1][4]
• Intraoral examination commonly discloses a carious or non-vital tooth—most often a mandibular first molar—with or without a draining sinus tract.[3][4]
• Trismus is uncommon in classic proliferative periostitis but may be present when the process extends posteriorly toward the ramus.[1]

Tempo and complications

• The condition follows a chronic, indolent course. Facial asymmetry is the primary concern, particularly in growing children.[2]
• Suppuration, fistula formation, and pathologic fracture are not features of proliferative periostitis and, if present, should prompt consideration of chronic suppurative osteomyelitis.[6]

Red flags

• Rapidly progressive swelling, paresthesia of the inferior alveolar nerve, tooth mobility without obvious periodontal disease, or systemic symptoms (fever, weight loss, night pain) should raise concern for malignancy or an aggressive infectious process and warrant urgent further investigation.[8][9]

Location and distribution

• Proliferative periostitis characteristically involves the inferior and buccal cortex of the posterior mandibular body, centered near the apices of the first or second permanent molar.[1][4]
• The process is localized, typically spanning one to three tooth widths along the mandibular body. Extension to the ramus or anterior mandible is occasional.[1][2]

Periphery and shape

• The outer margin of the periosteal new bone is well defined and runs parallel to the native cortex.[4]
• On panoramic radiography, one or more radiopaque lamellae are visible external to the inferior cortical border, separated from it by thin radiolucent lines representing the original periosteal space.[4]
• The overall contour may appear as a smooth convex enlargement or as distinct parallel layers, depending on the number of deposited lamellae.[4]

Internal architecture

• The characteristic internal pattern is lamellated (onion-skin) periosteal new bone: multiple thin, concentric radiopaque layers separated by radiolucent intervals, deposited on the outer cortical surface.[1][4][10]
• In early or mild cases, only a single radiopaque lamella may be visible.[4]
• With chronicity, the lamellae may merge into a solid, homogeneously radiopaque mass of new bone as the intervening spaces ossify.[4]
• The underlying medullary bone is typically normal or shows only mild, ill-defined periapical radiolucency related to the causative tooth. Extensive medullary osteolysis or sclerosis is not a feature of classic proliferative periostitis and suggests a different subtype of osteomyelitis.[1][6]

Effects on teeth and adjacent structures

• The causative tooth commonly shows deep caries, a large restoration, or periapical radiolucency consistent with pulp necrosis.[3][4]
• Displacement, root resorption, and loss of the lamina dura of adjacent teeth are not expected. Their presence should prompt reconsideration of the diagnosis.[1]
• The inferior alveolar canal is typically unaffected.[1]

Cortical involvement and extent

• The native buccal and inferior cortex remains intact beneath the periosteal new bone; cortical destruction or perforation is not a feature of uncomplicated proliferative periostitis.[1][4]
• Cross-sectional imaging demonstrates the layered new bone deposited on the external cortical surface, confirming that the expansion is periosteal rather than endosteal in origin.[1][2]
• In cases associated with chronic non-suppurative osteomyelitis, cross-sectional imaging may reveal small osteolytic foci within both the medullary bone and the newly formed periosteal bone, along with focal cortical perforations.[1]

Recognized variants (Kawai classification)

Kawai et al. classified periostitis ossificans of the mandible into two types based on whether the original mandibular contour is preserved:[4]

• Type I — original mandibular contour preserved:
  • Type I-1: a single radiopaque lamella outside the cortex
  • Type I-2: two or more distinct lamellae (classic onion-skin)
• Type II — original mandibular contour altered by the volume of new bone formation

The radiographic subtype may vary depending on the projection used; occlusal views and cross-sectional imaging often reveal additional lamellae not visible on panoramic radiography.[4]

MRI

When MRI is obtained—typically to exclude malignancy—proliferative periostitis shows low-to-intermediate signal on T1-weighted sequences and intermediate-to-high signal on T2-weighted and STIR sequences in the periosteal soft tissues and new bone, reflecting reactive edema and inflammation.[11] The absence of a sharply marginated intramedullary mass with a well-defined soft-tissue component helps distinguish the condition from Ewing sarcoma, in which a sharply defined intraosseous lesion margin on T1-weighted images is characteristic.[11] Masticatory muscle edema may be present but is typically mild compared with diffuse sclerosing osteomyelitis, which shows more prominent muscle hypertrophy and edema.[6]

The lamellated periosteal reaction and mandibular swelling in a child or adolescent generate a differential that spans reactive, neoplastic, and systemic entities. The key diagnostic task is to distinguish this benign, self-limiting process from aggressive conditions—particularly Ewing sarcoma—that can produce a similar onion-skin pattern.[10]

The highest-risk diagnostic pitfall is misidentifying Ewing sarcoma as proliferative periostitis, given the overlapping age group and the shared onion-skin periosteal pattern. When an identifiable odontogenic source is absent, the periosteal reaction is irregular or interrupted, or a soft-tissue mass is present, biopsy is mandatory before attributing the findings to a reactive process.[10][11]

Microscopic findings

• The hallmark is layers of viable reactive woven and lamellar bone deposited beneath a thickened, hyperemic periosteum.[3][5]
• The periosteal new bone is arranged in parallel lamellae separated by fibrovascular connective tissue, corresponding to the radiographic onion-skin pattern.[3][5]
• The intervening fibrous tissue contains dilated capillaries and a mild chronic inflammatory infiltrate composed predominantly of lymphocytes and plasma cells; neutrophils are sparse or absent in the non-suppurative form.[1][5]
• The underlying cortical and medullary bone may show features of chronic osteomyelitis, including irregular reversal lines, sclerotic trabeculae, and marrow fibrosis, but sequestra and microabscesses are not expected.[1][18]

Radiologic-pathologic correlation

The concentric bony lamellae seen histologically correspond directly to the radiopaque layers on imaging, while the intervening fibrovascular zones account for the radiolucent intervals. As the process matures, the lamellae coalesce into solid cortical-type bone, explaining the transition from a lamellated to a solid radiographic appearance.[4][5]

Diagnostic pitfalls

• Exuberant reactive new bone with osteoblastic activity can histologically mimic osteosarcoma; however, the absence of cytologic atypia, atypical mitoses, and malignant osteoid production distinguishes proliferative periostitis.[5][19]
• Correlation with clinical and radiographic findings is essential to avoid overdiagnosis of malignancy.[3][19]

Workup and referral

• Panoramic radiography is the initial imaging study. Cross-sectional imaging is indicated when the clinical or radiographic presentation is atypical, when malignancy cannot be excluded, or when the extent of disease needs clarification.[1][4]
• Vitality testing and periapical radiography of the suspected causative tooth should be performed to confirm the odontogenic source.[3][4]
• When no odontogenic source is identified, biopsy is recommended to exclude neoplastic and systemic conditions.[1][8]

Definitive treatment

• Elimination of the infectious source is the cornerstone of management: extraction of the non-restorable causative tooth or endodontic treatment if the tooth is salvageable.[2][3]
• Adjunctive antibiotic therapy (typically a penicillin-class agent) is commonly administered, though the periosteal reaction itself is a reparative response and resolves with source control.[2][3]
• Surgical decortication or debridement of the periosteal new bone is generally unnecessary; the reactive bone re