Non-ossifying fibroma (NOF) is one of the most common benign bone lesions of childhood and adolescence. It is considered a developmental bone defect of fibroblastic origin — not a true neoplasm. It presents as an eccentric cortical-based, sclerotic-bordered, 'bubbly' lytic lesion in the metaphysis of long bones. It is asymptomatic, incidentally discovered, and requires no treatment.
Age Range
5-25
Peak Age
12
Gender
Male predominant
Prevalence
Very Common
Non-ossifying fibroma is considered a local developmental anomaly of the periosteum or cortical bone in the growth plate (physis) region. Fibrous tissue formed by proliferation of fibroblasts, histiocytes, and multinucleated giant cells replaces normal bone formation — hence the name 'non-ossifying' (not forming bone). The lesion 'migrates' over time from the growth plate toward the meta-diaphyseal junction as the growing bone leaves the lesion behind. Eccentric cortical thinning and sclerotic border on CT reflect the slow growth and periosteal reactive bone formation of the lesion. The fibrous content of the lesion appears as low-to-intermediate signal on both T1 and T2 MRI because collagen fibers have both short T1 and short T2 relaxation. Hemosiderin deposition (hemosiderin-laden macrophages) creates the yellowish-brown color of the lesion and focal low signal areas on MRI.
Eccentric cortical-based, sharply sclerotic-bordered, multiloculated ('bubbly') lytic lesion in the metaphysis of a long bone. This appearance is pathognomonic for NOF and when combined with typical age group (5-20 years), diagnosis is certain. Cortical thinning is present but perforation and periosteal reaction are absent.
On CT, an eccentric cortical-based lytic lesion is seen in the metaphysis of a long bone. The lesion is surrounded by a sharp sclerotic border (Lodwick type IA). The interior is filled with low-density fibrous tissue. Cortical thinning (scalloping) is prominent but cortical perforation is absent. 'Bubbly' or 'multilocular' internal structure results from fibrous septa.
Report Sentence
On CT, an eccentric cortical-based lytic lesion with sharp sclerotic border is identified in the distal femoral metaphysis, with cortical thinning but no perforation; consistent with non-ossifying fibroma.
On T1-weighted series, NOF demonstrates low to intermediate signal intensity. The collagenous structure of fibrous tissue produces low T1 signal, while hemosiderin-laden macrophages and lipid-rich histiocytes create focal signal variations. Lesion margins are sharp, clearly separated from surrounding normal marrow fat signal. No periosteal edema or bone marrow edema.
Report Sentence
On T1-weighted series, the lesion demonstrates low to intermediate signal, clearly separated from surrounding normal marrow fat signal; no bone marrow edema is present.
On T2-weighted series, NOF demonstrates heterogeneous low to intermediate signal. Fibrous component (collagen) produces low T2 signal, while xanthomatous areas (lipid-rich histiocytes) and hemosiderin create focal signal variations. Unlike most benign bone lesions (simple cyst, aneurysmal bone cyst), NOF is not bright on T2 — this is an important distinguishing feature. No surrounding bone marrow edema.
Report Sentence
On T2-weighted series, the lesion demonstrates heterogeneous low to intermediate signal; the non-bright cortical-based lesion pattern on T2 is consistent with non-ossifying fibroma.
On STIR sequence, NOF shows low to intermediate signal without surrounding bone marrow edema. This feature is the most important STIR finding distinguishing NOF from aggressive lesions (osteosarcoma, Ewing sarcoma, osteomyelitis). Slight signal increase may occur during active growth phase but surrounding edema is still absent.
Report Sentence
On STIR sequence, the lesion shows low to intermediate signal without perifocal bone marrow edema; this finding is consistent with a benign indolent lesion.
On post-contrast series, NOF demonstrates minimal or no enhancement. Its fibrovascular stroma contains minimal vascularity. This finding distinguishes it from aggressive lesions that show enhancement (Ewing, osteosarcoma, osteomyelitis). In NOF complicated by pathologic fracture, surrounding reactive tissue may enhance.
Report Sentence
On post-contrast series, the lesion demonstrates no significant enhancement, consistent with an avascular/hypovascular benign lesion.
With age, NOF undergoes spontaneous ossification (involution). On CT, the peripheral sclerotic border progressively thickens and sclerosis develops in the lesion center. At complete involution, the lesion remains as a completely sclerotic area or is replaced by normal bone. This natural course confirms that NOF is developmental rather than neoplastic.
Report Sentence
On CT, progressive sclerosis from periphery to center is noted in the lesion, consistent with expected involution process of non-ossifying fibroma.
Criteria
<3cm size, entirely cortical location, no intramedullary extension, usually <10 years
Distinct Features
Considered the small version of NOF. On CT, small cortical defect; on radiograph, oval radiolucent area within intact cortex. Detected as incidental finding in 30-40% of children. No clinical significance, no intervention needed. Most spontaneously ossify within 2 years.
Criteria
>3cm size, cortical + intramedullary extension, adolescent age, pathologic fracture risk present
Distinct Features
Larger size and intramedullary extension make cortical weakening more prominent. Pathologic fracture risk: increased in NOFs involving >50% of bone diameter. Curettage + grafting may be needed in case of pathologic fracture. Fracture-free large NOFs are also generally followed conservatively.
Criteria
Multiple NOF + extra-osseous findings (cafe-au-lait spots, mental retardation, eye anomalies, cryptorchidism, cardiovascular malformations)
Distinct Features
Phenotype overlapping with neurofibromatosis type 1 (NF1). Bilateral NOFs in multiple bones. Presence of cafe-au-lait spots suggests NF1 but Jaffe-Campanacci is considered separate from NF1. Genetic counseling and multisystem evaluation recommended.
Distinguishing Feature
Fibrous dysplasia is intramedullary in location showing 'ground glass' density. NOF is eccentric cortical-based and completely lytic (no ground glass density). Fibrous dysplasia typically involves a wider segment and causes bone expansion. Sclerotic border is more prominent in NOF.
Distinguishing Feature
Aneurysmal bone cyst shows very bright T2 signal (fluid-fluid levels) and is an expansile lytic lesion. NOF is not bright on T2 (low-intermediate signal) and is not expansile. ABC has a more aggressive appearance and shows enhancement. NOF does not show enhancement.
Distinguishing Feature
Osteosarcoma shows aggressive bone destruction, periosteal reaction (sunburst, Codman triangle), and soft tissue mass. None of these are present in NOF. On MRI, osteosarcoma demonstrates prominent bone marrow edema and enhancement, while NOF shows neither edema nor enhancement. The sharp sclerotic border of NOF is absent in osteosarcoma.
Distinguishing Feature
Simple bone cyst is centrally (not eccentric) located and fluid-filled — homogeneously bright T2 signal, low T1 signal. NOF is eccentric cortical-based and not bright on T2. 'Fallen fragment' sign (after pathologic fracture) may be seen in simple bone cyst.
Urgency
non-urgentManagement
Tedavi gerekmez ('leave me alone' lezyon). Görüntüleme bulguları tipik ise biyopsi gerekmez. Patolojik fraktür riski varsa (>%50 kemik çapı) profilaktik küretaj + greftleme düşünülür. Patolojik fraktür oluşmuşsa tedavi fraktüre yöneliktir.Biopsy
Not NeededFollow-up
Tipik görünümde takip gerekmez. Atipik bulgular varsa (ağrı, büyüme, kemik iliği ödemi) 6-12 ay sonra kontrol görüntüleme. Patolojik fraktür riski olan büyük lezyonlarda klinik takip.NOF is in the category of 'don't touch' lesions — diagnosis is made by typical radiological appearance and biopsy is unnecessary. Eccentric cortical-based, sclerotic-bordered, bubbly lytic lesion + childhood/adolescent age group + metaphyseal location = clinical diagnosis. Unnecessary biopsy complications (pathologic fracture, infection) should be avoided. Jaffe-Campanacci syndrome (multiple NOF + cafe-au-lait) is a rare condition overlapping with NF1.
NOF does not require treatment and has no malignant transformation risk. Most heal by spontaneous ossification (after puberty). Pathologic fracture risk exists in large lesions (those occupying >50% of bone diameter). Biopsy is contraindicated in typical radiologic appearance (unnecessary).