DEFINITION

Avascular necrosis (AVN), also known as osteonecrosis or aseptic necrosis, is the death of bone tissue secondary to the interruption of the subchondral blood supply. It primarily affects the epiphysis of long bones in weight-bearing joints. Cessation of blood flow may be traumatic or non-traumatic [1, 2].

Histology. Histopathologically, osteocytes undergo apoptosis, and phagocytosis does not occur, preventing their replacement. As a result, this process leads to defective bone remodeling and osteosclerosis [3].

Prognosis. The prognosis for osteonecrosis is generally poor, regardless of initial treatment. Disease progression results in persistent pain, disability, and irreversible joint destruction [4].

Treatment. Core decompression and bone grafting can prevent the progression of osteonecrosis, but advanced cases or failed joint-preserving treatments require arthroplasty, which carries a higher risk of complications [5].

CLASSIFICATION - MRI FINDINGS

The imaging aspects of AVN can be classified using the Ficat and Arlet classification, which was first described in 1964. Since then, the system has been updated to include MRI findings, patient symptoms, revised radiographic descriptions, and exclude previously used invasive procedures [6].

There are five stages based on radiographic and clinical findings.

• Stage 0 represents the early stage of AVN, where both plain radiographs and MRI appear normal, and no clinical symptoms are present [7]. 
• In Stage I, plain radiographs may appear normal or show minor osteopenia. MRI reveals oedema. The clinical symptoms often include pain, typically localized to the groin area, in cases of avascular necrosis of the hip [7]. The first sign of AVN is nonspecific: diffuse low-signal areas in the normally high-signal fatty marrow on T1-weighted images [8].
• Stage II is characterized by mixed osteopenia and sclerosis, with or without subchondral cysts on plain radiographs, with no subchondral lucency. MRI shows a geographic defect. The ‘double line' sign appears in 80-85% of cases, consisting of an inner bright line (reparative granulation tissue) and an outer dark line (sclerotic bone).
  

  Fig 1: Stage II avascular necrosis (ax PD TSE FS, patella): double line sign: bright inner line (=granulation tissue, arrow); dark peripheral line (=sclerotic bone, arrowhead); References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  

  Fig 2: Stage II avascular necrosis (cor PD FS, tibia): double line sign: bright inner line (=granulation tissue, arrow); dark peripheral line (=sclerotic bone, arrowhead); References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  

  Fig 3: Stage II avascular necrosis (cor PD FS, femur): double line sign: bright inner line (=granulation tissue, arrow); dark peripheral line (=sclerotic bone, arrowhead); References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  The outer line is always continuous, while the inner line may be discontinuous or absent. This sign should not be mistaken for the ‘rim' sign, which indicates an unstable osteochondral fragment surrounded by fluid. Patients often experience pain and stiffness at this stage [7, 9].
• Stage III involves the development of the ‘crescent sign’ on plain radiographs, with eventual cortical collapse. MRI findings are similar to those seen on the radiographs. A ‘rim' sign, featuring a high T2 or intermediate T1 signal between two low signal lines, indicates fluid between sclerotic borders of an osteochondral fragment, suggesting instability.
  

  Fig 4: Stage III avascular necrosis (cor PD TSE FS, femur): rim sign: linear high signal intensity (=fluid, arrow) sandwiched between two low signal lines; References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  

  Fig 5: Stage III avascular necrosis (cor PD TSE FS, talus): rim sign: linear high signal intensity (=fluid, arrow) sandwiched between two low signal lines; References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  

  Fig 6: Stage III avascular necrosis (sag PD TSE FS, femur): cortical collapse (arrowhead); References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  

  Fig 7: Stage III avascular necrosis (sag PD TSE FS, talus): cortical collapse (arrowhead); References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  Clinical symptoms include stiffness and pain, which may radiate to the knee, along with a noticeable limp [7, 10].
• Finally, Stage IV represents the end stage of AVN. Plain radiographs show evidence of secondary degenerative changes, and MRI findings are consistent with the radiographs.
  

  Fig 8: Stage IV avascular necrosis (cor STIR, femur): bone deformity and secondary osteoarthritis; References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  

  Fig 9: Treated stage IV avascular necrosis (cor T1 TSE): hip prosthesis; References: Radiology, Medical Imaging and Interventional Radiology Department of Fundeni Clinical Institute, Bucharest, Romania
  Clinical symptoms include persistent pain and a limp [7] .

MATHERIALS AND METHODS

A retrospective study was conducted, including 54 patients treated at our university hospital between January 2015 and June 2024. All patients had a confirmed diagnosis of a malignant disease and were subsequently diagnosed with AVN based on MRI findings. The cohort had a male-to-female ratio of 1.07:1 and ages ranging from 15 to 86 years.

Key demographic data, including age, gender, and clinical history, were collected. In addition, the type of cancer diagnosed in each patient and their treatment regimens, particularly whether they had received corticosteroid therapy or radiotherapy, were documented. Corticosteroids are frequently prescribed as part of the treatment regimen for various hematological cancers (such as leukemia, lymphoma, and myeloma) [11]. Radiation-induced AVN is rare at lower doses, but such as corticosteroids, bone degeneration, and chemotherapy can contribute to ischemia and necrosis [12].

The study also involved a detailed analysis of the imaging characteristics of AVN using the Ficat and Arlet classification. This classification aimed to better understand the radiological presentation of AVN in patients with malignancies and to explore potential correlations between cancer treatment and the development of AVN. Through comprehensive data collection and analysis, the study sought to gain insights into the clinical and radiological patterns of AVN in this patient population.

MRI served as an essential diagnostic tool in this study, allowing for precise identification, classification, and evaluation of AVN in cancer patients, which would be difficult to achieve with other imaging methods.

The imaging protocol included sequences such as T1-weighted imaging (T1WI), T2WI, proton density (PD), and short tau inversion recovery (STIR), applied in different planes based on the evaluated segment. In general, non-contrast MRI examinations were performed, with a few being contrast-enhanced, the latter often performed due to suspicion of a tumor's presence.

EXCLUSION CRITERIA

• Severe renal or liver dysfunction. These conditions may affect the pharmacokinetics of corticosteroids or other treatments used in cancer therapy, potentially influencing the development of AVN.
• Co-existing systemic diseases (e.g., systemic lupus erythematosus, rheumatoid arthritis). These conditions may cause secondary AVN or interfere with the evaluation of AVN risk factors (e.g., disease-modifying drugs or steroids used for conditions other than cancer).
• Non-cancerous bone pathologies unrelated to AVN or cancer (e.g., osteomyelitis, Paget's disease). These conditions could complicate the interpretation of MRI findings.
• History of AVN from non-cancer causes. Patients who have been diagnosed with AVN due to factors unrelated to cancer or its treatment (e.g., alcohol use, trauma, or other metabolic disorders).