Brown tumor with primary hyperparathyroidism

The brown tumor is a non-neoplastic, reactive osteolytic lesion that represents the terminal expression of sustained parathyroid hormone (PTH) excess on bone.[1][2] In the primary hyperparathyroidism (PHPT) setting, chronically elevated PTH drives RANKL-mediated osteoclastic resorption, replacing marrow with richly vascularized fibrous tissue; recurrent microhemorrhage and hemosiderin deposition give the lesion its characteristic brown color.[1][3] It is not a true neoplasm and shares histology with other giant cell–rich lesions.[4]

• Biologic behavior: benign, metabolically driven, and typically reversible once the hyperparathyroid state is corrected.[2]
• Usual site: any bone may be involved; in the maxillofacial region the mandible (especially the posterior body) and the maxilla are the recognized sites, and a jaw lesion may be the first clinical sign of occult PHPT.[3][5]
• Signature imaging pattern: a well-defined, expansile lytic lesion against a background of generalized high-turnover change (ground-glass trabeculation, lamina dura loss).[1][6]
• Management direction: treat the hyperparathyroidism first; most lesions regress after parathyroidectomy, with local jaw surgery reserved for selected cases.[4][7]

• Accepted name: brown tumor of hyperparathyroidism. The lesion is one focal manifestation within osteitis fibrosa cystica (OFC), the broader skeletal syndrome of advanced PHPT; the two terms are often used interchangeably for the focal lesion but OFC properly denotes the generalized high-turnover bone disease.[1][8]
• Historical eponym: the condition was described by von Recklinghausen, and "von Recklinghausen disease of bone" is an obsolete eponym for osteitis fibrosa cystica and should be avoided because it is easily confused with neurofibromatosis type 1.[2]
• Classification context: the lesion is grouped among the giant cell–rich lesions of bone/jaws, which also include central giant cell granuloma (CGCG), giant cell tumor of bone, cherubism, and the solid variant of aneurysmal bone cyst; these are distinguished by clinical and molecular rather than purely morphologic criteria.[9][10]
• Etiologic qualifier: "primary" specifies PTH excess from autonomous parathyroid tissue (adenoma, hyperplasia, rarely carcinoma), distinguishing it from secondary and tertiary forms that are more often renal in origin.[2][11]

• Frequency: brown tumors complicate roughly 3% (reported 3–4.5%) of PHPT, and this classic manifestation has become uncommon in regions with routine serum calcium screening. Overt OFC now affects less than 2% of PHPT patients in the United States. Jaw involvement specifically is rarer still and signals advanced disease.[1][2][12][13]
• Geography: severe skeletal presentations persist where biochemical screening is limited and vitamin D deficiency is endemic (parts of Asia, the Middle East, South Africa, and Latin America), which materially raises the pretest probability of a jaw brown tumor in those populations.[2][12]
• Age and sex: maxillofacial brown tumors cluster in women in the third to fourth decades, mirroring the female predominance of PHPT, though lesions occur across adulthood and occasionally in children.[4][7]
• Anatomic distribution: across the skeleton, the pelvis, ribs, long bones, hands, and jaws are typical sites. Within the jaws, the mandible is frequently cited, but maxillofacial series also report the maxilla as a common location, and synchronous maxillary and mandibular lesions occur.[1][7][14]

• Presentation: a painless or mildly tender, slowly enlarging swelling producing facial asymmetry, cortical expansion, and sometimes a palpable or intraoral mass; the jaw lesion is not infrequently the initial manifestation that uncovers undiagnosed PHPT.[5][14]
• Dental findings: tooth mobility, migration or displacement, and malocclusion reflect alveolar bone involvement; widening of the periodontal ligament space and increased tooth loss have been documented in PHPT.[13][15][16]
• Systemic context: the lesion coexists with the hypercalcemic syndrome — fatigue, bone pain, nephrolithiasis/nephrocalcinosis, polyuria, constipation, peptic ulcer disease, proximal muscle weakness, and neurocognitive disturbance — and the biochemical hallmark is hypercalcemia with inappropriately elevated PTH and hypophosphatemia.[2][8][12]
• Tempo and complications: growth is usually indolent, but large lesions cause cortical thinning, pathologic fracture, and in the mandible rarely spontaneous fracture of the thinned lower border.[6]
• Red flags: marked hypercalcemia, rapidly progressive or multifocal lesions, and a palpable neck mass raise concern for severe disease or parathyroid carcinoma, which can present with florid multifocal brown tumors.[11]

Classically, a focal lytic jaw lesion appears on a background of generalized high-turnover bone change; when present, these generalized changes support the diagnosis, but their absence does not exclude it, and serum calcium and PTH are decisive.[1][6]

Location and distribution

• Favors the posterior mandible (body and ramus) but also arises in the maxilla; lesions may be solitary or multifocal, and jaw involvement may be unilateral or bilateral.[3][7]
• Multifocality anywhere in the skeleton should prompt correlation with PTH, because multiple lesions readily mimic metastatic disease.[2][11]

Relationship to teeth and alveolar process

• Centered in medullary bone, the lesion can extend to involve the alveolus and approach or displace adjacent molar and premolar roots.[4]
• Background alveolar changes include loss of the lamina dura and widening of the periodontal ligament space, regarded as early signs correlated with serum PTH.[15][16]

Periphery and shape

• Typically well defined with a narrow zone of transition and no periosteal reaction; margins may be corticated/sclerotic.[1][2]
• Shape is expansile and rounded to lobulated, often with a thin surrounding bony shell.[2]

Internal architecture

• Predominantly radiolucent; larger lesions may show a coarse trabeculated or soap-bubble/multilocular pattern.[1]
• The surrounding bone shows a ground-glass trabecular pattern with loss of normal fine trabeculation, reflecting high turnover.[3][6]

Effects on teeth and adjacent structures

• Root resorption, tooth displacement, and loss of lamina dura are the recognized dental effects; cortical destruction and tooth displacement are among the more frequently reported jaw findings.[15]
• Thinning and expansion of the mandibular cortices, reduced cortical thickness at the mandibular angle, and occasional obliteration of the inferior alveolar canal are described.[6][15]

Cortical involvement and extent

• Expansion with cortical thinning predominates; frank cortical breakthrough is uncommon and, when present, signals a large or aggressive lesion and raises the differential of malignancy.[1]
• Sectional imaging better delineates three-plane extent, cortical status, relationship to the maxillary sinus or alveolar canal, and any associated pathologic fracture.[1]

Associated skeletal signs and variants

• Supportive distant findings include the "salt-and-pepper" skull, subperiosteal resorption of the phalanges, and distal clavicular tapering.[8]
• Recognized variants are the solitary jaw lesion versus multifocal disease; the latter is the pattern most often mistaken for metastatic or marrow malignancy.[2][11]

Parathyroid localization

Once PHPT is biochemically confirmed, neck ultrasound and 99mTc-sestamibi scintigraphy localize the culprit adenoma, and 4-dimensional CT serves as a second-line study when initial imaging is nonlocalizing — guiding minimally invasive versus bilateral exploration. 18F-fluorocholine PET/CT can simultaneously localize the parathyroid source and demonstrate skeletal brown tumor foci.[4][17][18]

Whole-skeleton and fracture assessment

Because PHPT is a systemic bone disease, DXA (including distal radius, a cortical site) with vertebral fracture assessment characterizes overall skeletal involvement and fracture risk relevant to management decisions.[8]

A focal lytic jaw lesion with giant cell–rich histology is the diagnostic trap: brown tumor is morphologically indistinguishable from several giant cell lesions, so the decisive discriminator is the biochemical demonstration of PTH-dependent hypercalcemia rather than the biopsy itself.[2][4]

The highest-risk pitfall is treating a multifocal or solitary giant cell lesion as a primary bone neoplasm — leading to unnecessary resection, radiotherapy, or amputation — when a simple serum calcium and PTH panel would reveal the metabolic cause; PTH elevation separates brown tumor from malignant hypercalcemia, in which PTH is suppressed.[2][11]

• Core features: osteoclast-type multinucleated giant cells clustered around areas of hemorrhage, within a background of proliferating mononuclear spindled/fibroblastic cells and vascularized stroma, with abundant hemosiderin deposition.[2]
• Reactive, not neoplastic: the picture reflects accelerated resorption and reparative fibrosis rather than clonal tumor growth.[1]
• Radiologic-pathologic correlation: the vascular, hemorrhagic, giant cell content corresponds to the brown gross color and the expansile lytic imaging pattern.[1][2]
• Diagnostic limitation: histology cannot by itself distinguish brown tumor from CGCG, giant cell tumor, or solid aneurysmal bone cyst, so diagnosis requires integration with biochemistry; in giant cell tumor the giant cells are larger with more than 12 nuclei and evenly distributed, a useful but non-definitive clue.[4]
• Molecular correlation: mutations that define mimics — H3F3A in giant cell tumor, USP6 in aneurysmal bone cyst, and TRPV4/KRAS/FGFR1 in CGCG — are absent in brown tumor, supporting a molecular route to exclusion when morphology is ambiguous.[10][19]

• Workup and referral: confirm PTH-dependent hypercalcemia (serum calcium, PTH, phosphorus, 25-hydroxyvitamin D, 24-hour urine calcium/creatinine), then refer for parathyroid localization and endocrine/parathyroid surgery; multidisciplinary coordination between the oral/maxillofacial team and endocrine surgery is essential, with treatment of the hyperparathyroidism taking precedence over the jaw lesion.[7][8]
• Definitive treatment:parathyroidectomy to remove the adenoma or hyperplastic/carcinomatous tissue is the primary therapy; the jaw lesion itself usually requires no direct intervention.[2][4]
• Lesion response: brown tumors typically regress and remineralize after normalization of calcium and PTH, with jaw lesion regression reported over weeks to many months and remineralization on follow-up imaging; one maxillofacial series noted bone regeneration at the tumor site averaging about seven months.[7][14][20]
• Role of local surgery: conservative osteoplasty or curettage/resection is reserved for lesions that fail to regress, cause persistent functional or esthetic deficit, threaten fracture, or remain large; definitive rehabilitation (including implants) can follow once lesions resolve.[2][7][14]
• Selection factors and the pediatric exception: no validated scoring system defines which lesions need operative management; size, location, symptoms, and fracture risk guide decisions. In children and adolescents, definitive parathyroid surgery is generally recommended, and because a brown tumor indicates skeletal involvement, parathyroidectomy is indicated regardless of age; observation is reserved for asymptomatic PHPT without bone disease.[2][4]
• Perioperative caution: vitamin D repletion before surgery reduces postoperative hypocalcemia ("hungry bone") risk after parathyroidectomy.[4]
• Prognosis: outcome is favorable with cure of the hyperparathyroidism; recurrence of the bone lesion signals persistent or recurrent PTH excess. Multifocal or treatment-resistant disease should prompt evaluation for parathyroid carcinoma or hereditary syndromes such as MEN1/2/4 and hyperparathyroidism–jaw tumor (CDC73) syndrome, which carry distinct surveillance and prognostic implications.[4][11]

Hyperparathyroidism–jaw tumor syndrome

Germline CDC73 (HRPT2) mutations cause hyperparathyroidism–jaw tumor syndrome, featuring parathyroid adenomas (with elevated parathyroid carcinoma risk) and ossifying fibromas of the jaw; affected patients can also develop brown tumors, so loss of parafibromin on immunohistochemistry and lifelong surveillance are warranted when the syndrome is suspected.[4]

Distinguishing from secondary/tertiary forms

Jaw brown tumors in renal-driven secondary and tertiary hyperparathyroidism share identical histology and imaging; management centers on CKD-MBD control (phosphate binders, active vitamin D, calcimimetics), with subtotal or total parathyroidectomy when secondary HPT does not respond or for tertiary HPT, making the biochemical and clinical context decisive for correct treatment.[2][21]