Humeral head necrosis 

                                       Dr. KS Dhillon

Osteonecrosis of the humeral head is a disorder that involves osteocytes and the marrow. It is characterized by bone death. Osteonecrosis of the humeral head may be atraumatic or traumatic. Osteonecrosis of the humeral head can result in the collapse of the humeral head articular surface and joint destruction. Since the glenoid is less constrained it can therefore accept greater deformity of the humeral head. The scapula can compensate for some of the glenohumeral motion loss due to the osteonecrosis.

Traumatic osteonecrosis occurs due to disruption of the blood supply to the head caused by fracture or dislocation of the proximal humerus [1].  Atraumatic osteonecrosis involves abnormalities of humeral head blood flow. There are multiple etiologies but corticosteroid therapy is the most commonly reported cause. Atraumatic osteonecrosis can be bilateral and multifocal. Osteonecrosis is considered multifocal when three or more joints are involved. The femoral and humeral head are most often affected [2].

Disease prevention is important. Most cases can be treated successfully without surgical intervention. In other patients, prosthetic replacement may be necessary. Early identification of disease progression is important to treat symptomatic disease in the early stages, thereby avoiding arthroplasty.

Anatomy

The main blood supply to the head of the humerus is from the ascending branch of the anterior humeral circumflex artery. It enters the humeral head through the bicipital groove. A small amount of collateral flow is provided by the posterior humeral circumflex artery which pierces the rotator cuff attachments. The collateral flow about the proximal humerus is minimal. The intraosseous blood supply to the head comes from the arcuate artery.

Pathophysiology

The insult that initiates the avascular necrosis differ on the basis of causation. Fracture dislocation of the shoulder causes traumatic disruption of the proximal humeral vasculature. There are several theories of steroid-induced disease [3]. One of the proposed theories is that increased intraosseous fat cell size results in increased intraosseous pressure and fat embolism. Alcohol abuse also appears to work in a similar manner as steroids. Dysbarism causes cell death via air bubbles leading to congestion and ischemia. In patients with sickle cell disease, the sickled red blood cells cause infarcts in the subchondral bone.

Following the initial insult, the pathogenesis of the disease is the same, regardless of the cause. Death of the cells and marrow occurs. During the healing phase, the necrotic tissue is removed by bone resorption. Bone resorption leads to the weakening of the bone. The forces across the subchondral plate of the weakened bone result in microfractures and subsequent collapse. Progressive deformity of the humeral head causes changes in the glenoid leading to osteoarthritis of the shoulder joint. 

Etiology

Traumatic humeral head osteonecrosis results from disruption of the blood flow of the humeral head due to proximal humeral fracture or dislocation. There are a growing number of case reports that report shoulder osteonecrosis following arthroscopic rotator cuff surgery [4].   

There are multiple causes of atraumatic osteonecrosis. These include: 

• Steroid use

• Alcohol abuse

• Dysbarism

• Hemoglobinopathies

• Coagulopathies

• Gaucher disease

• Connective tissue disorders

• Idiopathic disorders [3,5].

 Adults with sickle cell disease are at higher risk for shoulder osteonecrosis if hip osteonecrosis is present or if they have the SC or S Beta genotype [6]. 

Epidemiology

The traumatic form of osteonecrosis has been reported in up to 34% of 3-part fractures and 90% of 4-part fractures of the proximal humerus, as well as nearly all fractures of the anatomic neck. The incidence of atraumatic osteonecrosis of the humeral head is difficult to determine. However, it occurs less often than in the hip. 

The traumatic form of shoulder osteonecrosis can occur at any age. The atraumatic form usually occurs in patients aged between 20-60 years. 

Clinical presentation

The presentation depends on etiology. Pain is usually poorly localized and severe. Rest pain and night pain are present. Pain increases with activity. The joint movements are preserved in the early stages of the disease. Following subchondral collapse, crepitation and locking are present. When arthritis sets in the joint movements are reduced.

Laboratory Studies

Laboratory studies are usually not necessary for the diagnosis of osteonecrosis. Tests can however be utilized to identify inciting factors, such as:

• Sickle cell disease in African Americans

• Lipid profile to reveal if there is underlying hyperlipidemia

• Thrombotic disorders - Protein S and protein C deficiencies, factor V Leiden disease

Imaging Studies

The diagnosis can be established in most of the cases by radiography. Essential radiographic views include anteroposterior (AP), and axillary views.

When humeral head osteonecrosis is suspected but the x-rays are normal magnetic resonance imaging (MRI) is the diagnostic modality of choice. MRI has sensitivity and specificity greater than 98% for humeral head osteonecrosis [7]. The extent of humeral head necrosis on MRI is a good predictor of future collapse of the humeral head [8].

A bone scan [7] can be useful when the disease is suspected clinically but is not apparent on radiographs. It is not commonly used because of the high success rate with MRI. 

Tomography can be useful in stage II disease to further define the lesion. 

Biopsy 

A biopsy can be performed at the time of surgery. The diagnosis is usually made based on clinical and radiographic findings.

Staging

Ficat and Arlet have staged osteonecrosis of the humeral head [9] :

Stage I - Normal

Stage II - Cystic and/or osteosclerotic lesions are seen. The humeral head contour is normal.

Stage III - There is subchondral collapse or crescent sign

Stage IV - There is narrowing of the joint space. Secondary osteoarthritic changes such as cysts, marginal osteophytes, and destruction of cartilage,

of the glenoid fossa and the glenohumeral head are seen. 

Treatment

Depending on the stage of the disease and the symptoms, the treatment of humeral head osteonecrosis varies. An important initial step is eliminating the inciting factor if and when it is recognized. Treatment often can be delayed or is not required because the shoulder is a non–weight bearing joint. When there is severe pain and/or mechanical symptoms, conservative and surgical options are available. The presence of infection or severe systemic disease may preclude surgical intervention.

Medical Care

Removal of the offending agent is the first line of treatment. Nonsurgical options are often more successful in cases of shoulder osteonecrosis because the shoulder is a non–weight-bearing joint. Physical therapy that includes modalities for pain control and range of motion exercises with muscle strengthening is helpful in all stages, particularly in stage I and stage II of the disease.

Alendronate is known to prevent a collapse of the femoral head caused by osteonecrosis. Its effectiveness in treating osteonecrosis of the shoulder is not known.

Surgical Care

Core decompression is performed in the early stage of the disease before the collapse of the head. The surgical procedure involves surgical drilling into the area of dead bone near the joint. This reduces pressure, allows for increased blood flow, and slows or stops bone and/or joint destruction. It allows bone healing. 

In 90% of cases of stage I and stage II disease core decompression have shown good and excellent results [10,11]. Core decompression can also be successful in stage III disease. There is, however, a 30% failure rate requiring subsequent arthroplasty in stage 3 disease. There is failure with core decompression in all cases of stage IV or V disease. The procedure is palliative only [12].  Harreld et al [13] have described an alternative technique of decompression utilizing multiple passes of a small-diameter (3-mm) drill in a percutaneous fashion. 

Mesenchymal stem cell grafting is also effective in treating posttraumatic shoulder osteonecrosis. A prospective randomized clinical study by Hernigou et al [14] of 50 patients with post-traumatic shoulder osteonecrosis compared the results of mesenchymal stem cell grafting of the humeral head versus simple core decompression. They found that after more than a decade of follow-up, the rate of collapse was significantly lower in the group treated with stem cells. Arthroscopic debridement of chondral lesions can be performed. Arthroscopy has no effect on the disease process. It may be helpful in dealing with mechanical symptoms. 

In patients with advanced-stage disease a hemiarthroplasty or total shoulder arthroplasty can be done depending on the condition of the glenoid [15,16,17]. A 90% success rate has been reported for hemiarthroplasty and total shoulder arthroplasty in advanced-stage disease. Most of them regain full movements of the shoulder [15,17]. Surface replacement arthroplasty also is an option [18,19].

Hemiarthroplasty has had a longer follow-up. Schoch and colleagues recommend that hemiarthroplasty should be considered in patients with atraumatic osteonecrosis of the humeral head with preserved glenoid cartilage [20]. 

Schoch et al [21] compared the outcome of 37 hemiarthoplasties with 46 total shoulder replacements performed for post-traumatic osteonecrosis of the humeral head after conservative treatments failed. They found that hemiarthroplasties provided improvements in range of motion and total shoulder replacement provided superior pain relief with better patient reported satisfaction.  

Core decompression is performed as follows:

The patient is placed in the beach-chair position with the arm over the edge of the table. A small incision is made in the lateral deltoid. Under image intensification guidance, a K-wire is inserted into the necrotic lesion, and a cannulated drill is used to take a core of bone. If the drilling technique is used multiple passes are made into the lesion with a small-diameter drill (usually 3.2 mm) under image intensification.

Arthroscopy can be used for intraarticular debridement. Articular cartilage flaps can be debrided, loose bodies removed, and selective capsular release can be performed.

Hemiarthroplasty involves the placement of a humeral head prosthesis, usually through a deltopectoral approach. 

For total shoulder arthroplasty, several prostheses are available. The glenoid is resurfaced with an all-polyethylene component. Total shoulder arthroplasty is required in individuals with stage IV disease.

When surface replacement arthroplasty is carried out the humeral head is resurfaced partially or completely with a metal component.

Postoperatively immediate range of motion (ROM) exercises can be initiated. Patients who had core decompression are started on immediate passive ROM exercises, with active ROM as tolerated. After full ROM is achieved, strengthening exercises can be started.

Following hemiarthroplasty and shoulder arthroplasty, immediate passive ROM exercises can be initiated. External rotation is limited to 45° for 6 weeks to allow for healing of the subscapularis. Active ROM can be started as tolerated. Strengthening is usually started 6 weeks after surgery.

Complications

Complications following surgery are rare. Common surgical complications include infection and neurovascular injuries. 

When core decompression is carried out care must be taken to avoid injury to the axillary nerve anteriorly. Penetration of the humeral head during core decompression should be avoided.

Complications with arthroplasty include prosthetic loosening, dislocation, and intraoperative fracture. 

References

1. Patel S, Colaco HB, Elvey ME, Lee MH. Post-traumatic osteonecrosis of the proximal humerus. Injury. 2015 Jun 19. 

2. El Gamal TA, El-Bakoury A, Hawkins A, Ed AlTayeb Mussa M, Er Ahmed Sweed T, Eh Samir Ansara S. Bilateral Osteonecrosis of the Femoral and Humeral Heads after Short Term Corticosteroid Therapy. A Case Study. Ortop Traumatol Rehabil. 2016 Mar 23. 18 (2):187-190.

3. Cruess RL. Experience with steroid-induced avascular necrosis of the shoulder and etiologic considerations regarding osteonecrosis of the hip. Clin Orthop Relat Res. 1978 Jan-Feb. 86-93.

4. Keough N, Lorke DE. The humeral head: A review of the blood supply and possible link to osteonecrosis following rotator cuff repair. J Anat. 2021 Nov. 239 (5):973-982.

5. Cushner MA, Friedman RJ. Osteonecrosis of the Humeral Head. J Am Acad Orthop Surg. 1997 Nov. 5(6):339-346.

6. Hernigou P, Hernigou J, Scarlat M. Shoulder Osteonecrosis: Pathogenesis, Causes, Clinical Evaluation, Imaging, and Classification. Orthop Surg. 2020 Oct. 12 (5):1340-1349.

7. Mont MA, Ulrich SD, Seyler TM, Smith JM, Marker DR, McGrath MS, et al. Bone scanning of limited value for diagnosis of symptomatic oligofocal and multifocal osteonecrosis. J Rheumatol. 2008 Aug. 35(8):1629-34. 

8. Sakai T, Sugano N, Nishii T, Hananouchi T, Yoshikawa H. Extent of osteonecrosis on MRI predicts humeral head collapse. Clin Orthop Relat Res. 2008 May. 466(5):1074-80.

9. Ficat RP, Arlet J. Necrosis of the femoral head. Hungerford DS. Ischemia and necrosis of bone. Baltimore, MD: Williams & Wilkins; 1980. 171-82.

10. LaPorte DM, Mont MA, Mohan V, Pierre-Jacques H, Jones LC, Hungerford DS. Osteonecrosis of the humeral head treated by core decompression. Clin Orthop Relat Res. 1998 Oct. 254-60. 

11. Mont MA, Maar DC, Urquhart MW, Lennox D, Hungerford DS. Avascular necrosis of the humeral head treated by core decompression. A retrospective review. J Bone Joint Surg Br. 1993 Sep. 75(5):785-8.

12. Soohoo NF, Vyas S, Manunga J, Sharifi H, Kominski G, Lieberman JR. Cost-effectiveness analysis of core decompression. J Arthroplasty. 2006 Aug. 21(5):670-81.

13. Harreld KL, Marulanda GA, Ulrich SD, Marker DR, Seyler TM, Mont MA. Small-diameter percutaneous decompression for osteonecrosis of the shoulder. Am J Orthop (Belle Mead NJ). 2009 Jul. 38 (7):348-54.

14. Hernigou P, Hernigou J, Scarlat M. Mesenchymal stem cell therapy improved outcome of early post-traumatic shoulder osteonecrosis: a prospective randomized clinical study of fifty patients with over ten year follow-up. Int Orthop. 2021 Oct. 45 (10):2643-2652.

15. Feeley BT, Fealy S, Dines DM, Warren RF, Craig EV. Hemiarthroplasty and total shoulder arthroplasty for avascular necrosis of the humeral head. J Shoulder Elbow Surg. 2008 Sep-Oct. 17(5):689-94.

16. Smith RG, Sperling JW, Cofield RH, Hattrup SJ, Schleck CD. Shoulder hemiarthroplasty for steroid-associated osteonecrosis. J Shoulder Elbow Surg. 2008 Sep-Oct. 17(5):685-8. 

17. Tauber M, Karpik S, Matis N, Schwartz M, Resch H. Shoulder arthroplasty for traumatic avascular necrosis: predictors of outcome. Clin Orthop Relat Res. 2007 Dec. 465:208-14.

18. Raissp, Kasten p, Baumann F, Moser M, Rickert M, Loew M. Treatment of osteonecrosis of the humeral head with cementless surface replacement arthroplasty. JBJS(Am). Feb 2009. 91(2):340-9. 

19. Uribe JW, Botto-van Bernden A. Partial humeral head resurfacing for osteonecrosis. J Shoulder Elbow Surg. Sept-Oct 2009. 18(5):711-6.

20. Schoch BS, Barlow JD, Schleck C, Cofield RH, Sperling JW. Shoulder arthroplasty for atraumatic osteonecrosis of the humeral head. J Shoulder Elbow Surg. 2016 Feb. 25 (2):238-45.

21. Schoch BS, Barlow JD, Schleck C, Cofield RH, Sperling JW. Shoulder arthroplasty for post-traumatic osteonecrosis of the humeral head. J Shoulder Elbow Surg. 2016 Mar. 25 (3):406-12.

 

          Osteoblastoma

                                     Dr. KS Dhillon

Introduction

Osteoblastoma is an uncommon benign bone-forming neoplasm. It accounts for about 1% of all primary bone tumors, 10% of all osseous spinal neoplasms, and 1 to 5 % of all benign bone tumors [1-3]. There are histopathologic similarities to an osteoid osteoma and hence, historically, it was referred to as giant osteoid osteoma [4].

There are some authors who consider these two entities to be variant expressions of the same pathologic process. The prevailing opinion, however, is that they are distinct pathologic entities with varying clinical presentations.

Osteoblastoma usually arises in the posterior elements of the spine and the sacrum (about 30 to 40%) [5]. Other common locations include the mandible and long tubular bones, where it is usually seen in the metadiaphysis [4]. An accurate diagnosis of osteoblastoma is important before appropriate treatment can be given and prognosis determined [6]. 

The diagnosis is usually made from clinical, radiological, and histopathological examination. The radiological appearance of the osteoblastoma is variable ranging from indolent to very aggressive [7].

The prognosis is usually good in patients with osteoblastoma. Patients are usually cancer-free after surgical treatment with intralesional curettage or marginal en bloc resection [8]. In patients with osteoblastoma that is not amenable to surgical excision, radiotherapy can be given. There are 2 borderline osteoblastic tumors i.e aggressive (epitheliod) osteoblastoma or osteoblastoma-like osteosarcoma, that must be differentiated from osteoblastoma with more aggressive presentation [9]. Occasionally osteoblastoma can be associated with systemic symptoms such as weight loss, fever, and diffuse periostitis, referred to as toxic osteoblastoma [10].

Etiology

The exact etiology of osteoblastoma is not known. FOS expression has been reported in osteoblastomas, and this suggests that fluorescence in-situ hybridization analysis for FOS rearrangement could be helpful in cases with worrying histologic features [11].

Epidemiology

Osteoblastoma is an uncommon benign bone-forming neoplasm. It accounts for about 1% of all primary bone tumors, 10% of all osseous spinal neoplasms, and 1 to 5 % of all benign bone tumors [1-3]. It mainly affects adolescents and young adults with a mean age of 20 years. There is a male predominance of 2.5 to 1. The more aggressive forms are usually seen in slightly older patients, with a mean age of 33 years [3,12]. Osteoblastomas can involve any bone. It, however, has a predilection for the spine and the sacrum (40 to 55%). It most commonly involves the posterior elements of the spine [13]. Other common sites include the facial bones and the long bones with a predilection for the lower extremity [4]. 

Less commonly it involves the tarsal bones (talus and calcaneum). There are case reports of involvement of the carpal bones and phalanges [14,15]. The bone location of the osteoblastoma can be cortical, medullary, or rarely periosteal [16].

Pathophysiology

Just like osteoid osteomas, osteoblastoma demonstrates marked new bone formation. This process is generally more exuberant in osteoblastoma, and the lesions tend to be more vascularized [17].

The nidus within osteoblastoma has less organized osteoid and trabecular bone, less abundant nerve fibers, and lacks prostaglandins as seen in osteoid osteomas [8,18]. Osteoblastomas often cause significant bone destruction, infiltration of the soft tissues, and epidural extension. They often show aggressive behavior with uncontrollable local recurrence. Malignant transformation, as well as metastatic diseases, have been reported with osteoblastoma [3,19].

The lack of prostaglandin production accounts for the variation in clinical presentation between osteoid osteoma and osteoblastoma, especially the nighttime pain that is relieved by salicylates, which is seen in patients with osteoid osteoma. Patients with osteoblastoma are usually asymptomatic or have dull, localized pain, which rarely interferes with sleep [20,21]. Both osteoblastoma and osteoid osteoma express Osterix and Runx2 transcription factors involved in osteoblastic differentiation [22].

Clinical presentation

Osteoblastomas grow slowly with minimal or no symptoms. The lesions are usually found incidentally during imaging for other diseases. Patients with osteoid osteoma are slightly younger and they have night-time pain that is relieved by salicylates [20,23]. 

Sometimes patients with osteoblastoma are symptomatic and they present with dull, localized pain. In some patients, the lesions are tender on palpation and present with soft tissue swelling [20]. 

Osteoblastomas of the spine can present with back pain, scoliosis, and nerve root compression [23,24]. Nerve root compression can lead to muscle weakness or paraplegia [25]. Toxic osteoblastoma is a rare variant of osteoblastoma. It can be associated with systemic symptoms, including fever, weight loss, anorexia, and diffuse periostitis [26]. 

Osteoblastomas usually do not extend into the surrounding soft tissues and generally do not produce soft tissue edema or inflammatory response. The prognosis is generally favorable, although local recurrence has been reported in about 25% of the cases [27]. There have been rare case reports of malignant degeneration over the years. Recent genomic studies, however, contradict these reports [28,29].

Evaluation

Modalities that are available for establishing the diagnosis of osteoblastoma include:

• Plain radiographs

• Computed tomography (CT)

• Magnetic resonance imaging (MRI)

It can be difficult on imaging to distinguish an osteoblastoma from an osteoid osteoma [7]. The lesions are usually radiolucent, round to oval, with well-defined margins, and with reactive sclerosis [3]. The imaging appearance may vary with the patient’s age and lesion maturity. The lesions are more often radiolucent in young patients and have increased sclerosis/ossification in older patients. There is thinning of the cortex but destruction or disruption of the cortex is only rarely seen in about 20% of cases [3]. In patients with disruption of the cortex, the lesions can be mistaken for a malignant process. Benign periosteal reaction is common and is seen in up to 86% of cases [3]. Generally, the lesions in the spine, pelvis, and talus demonstrate less surrounding reactive bone formation as compared to lesions of the long bones [21].

Radiographs (X-ray)

Plain film radiography is generally used for the diagnosis of osteoblastoma (fig 1). The radiographic appearance can vary slightly. Four distinctive radiographic presentations have been described [3,21]. 

1. A radiographic appearance similar to an osteoid osteoma but larger in size (>2 cm), with less reactive surrounding sclerosis and more overlying periostitis.

2. A blown-out expansile lesion mimicking an aneurysmal bone cyst. This pattern is most commonly seen in lesions of the axial skeleton [30].

3. Aggressive appearing lesions that mimick a malignant process with cortical expansion, thinning, or disruption, as well as extensive periostitis and large size (often greater than 4 cm). Aggressive osteoblastomas generally fall into this category. Some authors believe that aggressive osteoblastomas are a distinct entity as opposed to a subtype of osteoblastoma [9][31].

4. Juxtacorticl or periosteal lesions are exceedingly rare, comprising 8 of 62 osteoblastoma cases in the literature [12,32]. These lesions have a thin periosteal margin but lack the exuberant surrounding sclerosis that is seen in most lesions [18].

Fig 1

Computed Tomography Scan

CT imaging has a complementary role to plain-film radiography in the diagnosis of osteoblastoma. The imaging appearance is similar to those described for radiography. The CT scan can help further characterize the lesions, specifically the size, exact location, presence, or extent of cortical disruption and the presence of a soft tissue component [33]. A CT scan is also useful for characterizing lesions present in locations that are suboptimally evaluated on radiographs due to overlapping/superimposed structures, such as lesions in the spine or pelvis [23].

Magnetic Resonance Imaging

MRI can characterize the extent of the lesion and the presence of aggressive imaging features. The contrast resolution on MRI allows for identifying reactive soft tissue edema and better evaluates the soft tissue component if present. Perilesional edema and extension into the surrounding soft tissues are rare with osteoblastoma. 

Nuclear Medicine Imaging 

Nuclear medicine imaging is generally not employed to evaluate osteoblastomas. Studies using technetium-99m will demonstrate increased uptake in the mass corresponding to the osteoid formation within the lesion. FDG-PET studies have revealed a high uptake in the tumor despite its pathologically benign features [34].

Treatment 

Osteoblastomas are treated by surgery. Surgery involves either en bloc resection or curettage, depending on the clinical situation, location within the bone, and suspicion of malignancy [35,36]. En-bloc resection is the preferred treatment whenever it is possible. En-bloc resection results in a lower risk of local recurrence than curettage. Recurrence rates as high as 25% have been reported. Multiple episodes of local recurrence are known to occur. There is no definite role for adjuvant radiotherapy or chemotherapy [27,37]. 

Sometimes imaging surveillance is necessary due to the risk of local recurrence. There are case reports in the literature on malignant degeneration. However, recent genomic studies contradict these findings [26,27].

Differential Diagnosis

The histological differential diagnosis of osteoblastomas includes:

• Osteoid osteoma

• Aneurysmal bone cyst

• Osteoma with osteoblastoma-like features

• Osteoblastoma-like osteosarcoma [38]

• Giant cell tumor of bone

The radiological differential diagnosis includes:

• Osteoid osteoma

• Osteosarcoma

• Aneurysmal bone cyst

• Infection (Brodie abscess)

• Metastasis [7]

Osteoid Osteoma

Osteoid osteoma and osteoblastoma can have a similar appearance in imaging studies and histology. Osteoid osteoma is more common in the appendicular skeleton whereas osteoblastoma commonly involves the spine and craniofacial structures specifically the mandible. Both can present with pain. Osteoblastoma is usually asymptomatic or only mildly symptomatic. Unlike osteoid osteoma, the pain due to osteoblastoma is not relieved by salicylates and is not disruptive to sleep. Osteoid osteomas can resolve/regress spontaneously and, therefore, in some cases, are treated symptomatically, while others are treated with percutaneous radiofrequency ablation. Osteoblastoma does not resolve/regress and degeneration into osteosarcoma has been reported, although this has been disputed [29,39]. 

Osteoblastomas are usually greater than 2 cm in size, while osteoid osteomas are smaller lesions. There can be subtle differences in the nidus' appearance, which may allow for distinguishing osteoid osteoma from osteoblastoma. The nidus of osteoid osteoma is more organized with a thin peripheral fibrovascular rim and a zonal pattern with central mineralization. On the other hand, osteoblastomas generally lack the fibrovascular rim and exhibit a lobulated or multifocal appearance [8,40].

Aneurysmal Bone Cyst

About 81% of aneurysmal bone cysts (ABC) occur as a primary benign osseous lesion. ABCs can secondarily arise from preexisting lesions such as osteoblastoma, giant cell tumor, chondroblastoma, and fibrous dysplasia. The radiographic appearance is that of an eccentric medullary-based, expansile, lucent lesion which has a thin cortex and well-defined, thin sclerotic margins. ABCs usually occur in the metaphysis of long bones (50 to 60%) but can also occur in the spine and sacrum (20 to 30%), predominately in the posterior elements. In 12 to 18% of the cases, the lesions can be cortically located, and in 7 to 8% of the cases, it can be located periosteally [41,42]. 

Cross-sectional imaging (CT and MRI) usually shows fluid-fluid levels and internal septations. Histopathology will show multiple blood-filled sinusoidal spaces with fibrous septations/walls, which may contain osteoid tissue, hemosiderin or reactive foam cells, and mature bone collections. There may also be richly vascularized solid components containing numerous giant cells [43]. ABCs are usually treated with curettage and bone grafting.

Giant Cell Tumor

Giant cell tumors are common benign osseous neoplasms. Eighteen to twenty percent of benign osseous tumors are giant cell tumours. They involve the metaphysis of long bones and extend to the epiphysis. They are often close to the articular surface with well-defined margins without significant surrounding sclerosis.

There is a female predilection of 3 to 1 and the peak incidence is between 20 to 30 years of age [44]. These features are different from that of osteoblastomas which have a male predominance, a peak incidence in the second decade, diaphyseal-metaphyseal location, and sclerotic margins with reactive periostitis. Periostitis can be seen in patients with giant cell tumors if there is an associated pathologic fracture. Microscopically giant cell tumors have giant cells evenly distributed throughout spindle cell stromal tissue. Rarely there is small amounts of osteoid formation [45].

Infection (Brodie abscess)

Brodie abscess is a subacute or chronic form of osteomyelitis. It usually occurs in pediatric patients prior to the closure of the growth plate. It can, however, occur in patients of any age. It presents as a radiolucent lesion, in the metaphysis of tubular bones. It is most often seen in the tibia. There is a 2 to 1 male predilection.

Patients usually present with pain and/or swelling. Most of the patients are afebrile, and less than half have elevated inflammatory markers. X-rays in skeletally immature patients will show a serpentine tract extending to the closest physis, periostitis, and adjacent soft tissue swelling with sclerotic margins. The penumbra sign, a rim of T1 hyperintense signal lining the abscess, is a distinguishing imaging feature on MRI.

Osteoblastoma-like osteosarcoma and Aggressive Osteoblastoma

These lesions represent unique borderline entities. They are not subtypes of osteoblastoma. These borderline lesions are exceedingly rare. An open biopsy instead of a percutaneous image-guided biopsy is necessary to establish the diagnosis.  In one study, only 36% of osteoblastoma-like osteosarcoma lesions demonstrated aggressive imaging features. 

Osteosarcoma

There are several subtypes of osteosarcomas with varied imaging and clinical presentations. Generally, osteosarcomas have a more aggressive appearance than osteoblastoma. The aggressiveness of the lesion is first characterized by radiographic imaging. Non-aggressive lesions have a well-defined narrow zone of transition with or without a sclerotic margin. Aggressive lesions will have incomplete or poorly defined margins with a wide zone of transition. Osteosarcomas will present with aggressive forms of periostitis, such as an "onion-skin or sunburst" appearance. Telangiectatic osteosarcoma, like conventional osteosarcoma, will have a more aggressive appearance than most osteoblastomas. Telangiectatic osteosarcoma will present as an expansile, lucent lesion with thin septations. An open biopsy may be needed to make an appropriate diagnosis.

Prognosis

The prognosis of osteoblastoma is excellent. Most patients are cured following the initial surgical treatment. Local recurrence is a relatively common complication, with rates ranging from 15% to 25% [13]. 

Recurrence is more common when the osteoblastoma is treated with curettage. Spinal lesions are often treated with curettage due to the anatomic challenges and morbidity of performing wide local excision. Hence, the high recurrence rates have been associated with spinal lesions. Recurrence is usually common in the first 2 years following treatment. After 2 years post-treatment recurrence is rare. Long-term follow-up imaging and clinical surveillance are necessary for at least 2 years to detect recurrence [37]. Degeneration into osteosarcoma has been reported in the literature, but recent genomic studies contradict these findings [3,38]. 

Complications

The most frequently encountered postoperative complications following surgical removal of osteoblastoma are:

• Wound infections

• A loss of stability involving the surgical stabilization construct

• Surgical site hemorrhage 

Tumor recurrence typically occurs late (i.e. months to years) after the surgery. There are no universally accepted time intervals to define this period.

References

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2. Wu M, Xu K, Xie Y, Yan F, Deng Z, Lei J, Cai L. Diagnostic and Management Options of Osteoblastoma in the Spine. Med Sci Monit. 2019 Feb 20;25:1362-1372. 

3. Lucas DR, Unni KK, McLeod RA, O'Connor MI, Sim FH. Osteoblastoma: clinicopathologic study of 306 cases. Hum Pathol. 1994 Feb;25(2):117-34.

4.  McLeod RA, Dahlin DC, Beabout JW. The spectrum of osteoblastoma. AJR Am J Roentgenol. 1976 Feb;126(2):321-5. 

5. Murphey MD, Andrews CL, Flemming DJ, Temple HT, Smith WS, Smirniotopoulos JG. From the archives of the AFIP. Primary tumors of the spine: radiologic pathologic correlation. Radiographics. 1996 Sep;16(5):1131-58. 

6. Manjunatha BS, Sunit P, Amit M, Sanjiv S. Osteoblastoma of the jaws: report of a case and review of literature. Clin Pract. 2011 Sep 28;1(4):e118.

7. Sharma V, Chew FS, Hoch B. Periosteal osteoblastoma: Multimodal imaging of a rare neoplasm. Radiol Case Rep. 2009;4(4):329. 

8. Atesok KI, Alman BA, Schemitsch EH, Peyser A, Mankin H. Osteoid osteoma and osteoblastoma. J Am Acad Orthop Surg. 2011 Nov;19(11):678-89. 

9. Ozger H, Alpan B, Söylemez MS, Ozkan K, Salduz A, Bilgic B, Sirin BK. Clinical management of a challenging malignancy, osteoblastoma-like osteosarcoma: a report of four cases and a review of the literature. Ther Clin Risk Manag. 2016;12:1261-70.

10. Theologis T, Ostlere S, Gibbons CL, Athanasou NA. Toxic osteoblastoma of the scapula. Skeletal Radiol. 2007 Mar;36(3):253-7.

11. Amary F, Markert E, Berisha F, Ye H, Gerrand C, Cool P, et al. FOS Expression in Osteoid Osteoma and Osteoblastoma: A Valuable Ancillary Diagnostic Tool. Am J Surg Pathol. 2019 Dec. 43 (12): 1661-1667.

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