24 Primary and Metastatic Tumors of the Hip

Yale A. Fillingham, Matthew Colman

24 Primary and Metastatic Tumors of the Hip

Benign

I. Enneking staging system for benign bone tumors ¹ :
1. The staging system for benign bone tumors utilizes an Arabic numerical, which differentiates the staging system from the malignant bone tumor staging system based on Roman numerical.
2. Stages 1 to 3 of the Enneking staging system:
  1. Stage 1 (latent):
    1. Defined as a benign bone tumor that maintains a consistent size or has a natural history of spontaneous resolution. Examples: enchondroma and nonossifying fibroma (NOF).
  2. Stage 2 (active):
    1. Defined as a benign bone tumor that has progressively grown in size but will be confined by anatomic barriers. Examples: unicameral bone cyst (UBC) and aneurysmal bone cyst (ABC).
  3. Stage 3 (locally invasive):
    1. Defined as a benign bone tumor that has progressively grown in size without being confined by anatomic barriers. Examples: giant cell tumor (GCT).
II. Synovial lesions:
1. Pigmented villonodular synovitis (PVNS) ² :
  1. Clinical presentation:
    1. Most common age group is middle-aged adults with a higher incidence among males than females.
    2. Typically only a single joint will be involved, most commonly the hip or knee.
    3. Patients will commonly have joint pain along with intermittent joint effusion and stiffness. A joint aspiration will typically be bloody in nature.
  2. Diagnostics:
    1. Radiographs:
      - i. Plain film radiographs can show swollen soft tissue or juxtacortical erosions and sclerotic margins.
    2. MRI:
      - i. Intra-articular lesion with low intensity (dark) on both T1- and T2-weighted images secondary to the large quantity of hemosiderin in the tumor.
    3. Histopathology:
      - i. Disease will commonly be diffused throughout the joint, but it is possible to have only a localized area within the joint.
      - ii. Histopathology will demonstrate highly cellular tissue with lipid-laden histiocytes, giant cells, and areas of chronic inflammation. The high cellularity will mimic sarcoma.
      - iii. Due to the high vascularity, the tissue will classically have large amounts of hemosiderin.
  3. Treatment and prognosis:
    1. Total synovectomy is the treatment of choice.
    2. Due to the difficulty of achieving a total synovectomy, the rates of recurrence can be greater than 50%.
    3. Often the natural history of PVNS will cause premature degenerative joint disease leading to definitive management with a total hip arthroplasty.
2. Synovial chondromatosis ³ :
  1. Clinical presentation:
    1. Presents in a wide age range of typically 20 to 70 years. Most cases are isolated to large joints with a relatively even split between the hip and knee.
    2. Common complaints include an insidious onset of pain and swelling of the joint. Patients often report mechanical symptoms secondary to the presence of loose bodies.
  2. Diagnostics:
    1. Radiographs:
      - i. Plain film radiographs will have areas of calcifications around the joint of varying sizes representing the loose bodies ( Fig. 24.1 ).
        
        Fig. 24.1 Anteroposterior pelvis of a patient with synovial chondromatosis and severe degenerative joint disease of the left hip (a) that was treated with a total hip arthroplasty (b).
    2. Histopathology:
      - i. The origin of synovial chondromatosis is the development of hyaline cartilage nodules from undifferentiated mesenchymal cells embedded in the synovium.
      - ii. The loose bodies will have areas of hyaline cartilage with varying degrees of calcification secondary to endochondral ossification.
  3. Treatment and prognosis:
    1. Total synovectomy with removal of the loose bodies is the treatment of choice. Due to size limitations of arthroscopic removal of loose bodies, it can often necessitate an open synovectomy and removal of loose bodies.
    2. Due to the difficulty of achieving a total synovectomy, recurrence of the disease is common.
    3. Despite removal of the loose bodies, the high rates of recurrence can cause early degenerative joint disease requiring a total hip arthroplasty.
III. Fibrous lesions of the bone:
1. UBC ⁴ :
  1. Clinical presentation:
    1. Common among individuals younger than 20 years with a propensity to occur in the proximal femur and humerus.
    2. UBC is usually discovered incidentally or as the result of a pathologic fracture.
  2. Diagnostics:
    1. Radiographs:
      - i. Plain film radiographs will show a centrally located single metaphyseal cyst (possible for cyst to appear multilobulated).
      - ii. Cyst will initially be located adjacent to the physis and gradually migrate away from the epiphysis. Although the cyst can appear expansile, it will rarely expand beyond the width of the physis.
      - iii. Pathognomonic symbol on plain film radiographs is the “fallen leaf” sign that represents a fractured fragment of cortical bone that has fallen into the cyst ( Fig. 24.2 ).
    2. MRI:
      - i. The cyst will have a homogeneous high intensity on T2-weighted images. It can mimic the fluid–fluid levels of an ABC following a pathologic fracture of the cyst.
    3. Histopathology:
      - i. The cystic fluid will appear similar to synovial fluid with the cyst having a thin fibrous membrane that can contain occasional giant cells.
  3. Treatment and prognosis:
    1. Lesions will typically regress spontaneously with physeal closure.
    2. Pathologic fractures are treated no different than a traumatic fracture.
    3. Impending pathologic fractures can be treated with prophylactic fixation.
      
      Fig. 24.2 Radiograph of the humerus demonstrates a fallen leaf sign representing the fractured cortex of the unicameral bone cyst.
2. ABC ⁵ :
  1. Clinical presentation:
    1. Usually present in patients younger than 20 years, with the proximal femoral metaphysis, proximal tibia, and distal femur being the three most common locations.
    2. It is possible for the lesion to be discovered incidentally, but patients will often complain of vague pain in the hip.
  2. Diagnostics:
    1. Radiographs:
      - i. Plain film radiographs will show an eccentrically located single multilobulated expansile metaphyseal cyst (can have internal trabeculae).
    2. MRI:
      - i. Classically described as having fluid–fluid levels representing the mixed blood and fluid composite of the cyst ( Fig. 24.3 ).
    3. Histopathology:
      - i. The cyst will have no endothelial, but the septa will have giant cells and immature osteoid matrix.
      - ii. The multilobulated structures will have blood-filled areas representing the classically described “lakes of blood.”
  3. Treatment and prognosis:
    1. Because the lesion is considered locally aggressive, it is treated in the proximal femur with curettage, bone grafting, and prophylactic fixation.
    2. Recurrence rates are approximately 20% with higher rates of 50% in young children with open physes.
      
      Fig. 24.3 Coronal T2 MRI image of a left proximal femur demonstrating the multiple fluid–fluid levels characteristic of aneurysmal bone cyst lesions.
3. Fibrous dysplasia ⁶ :
  1. Clinical presentation:
    1. Presents in patients younger than 30 years, most commonly in the proximal femur.
    2. Most lesions are asymptomatic and found as incidental lesions on plain film radiographs.
    3. McCune–Albright syndrome is a combination of fibrous dysplasia, coast of Maine café au lait spots, and endocrinopathy (usually precocious puberty).
    4. Mazabraud’s syndrome is a clinical entity of polyostotic fibrous dysplasia associated with intramuscular myxomas.
  2. Diagnostics:
    1. Radiographs:
      - i. Lesions can be present in the proximal femur metaphysis or diaphysis with a “ground-glass” appearance secondary to the small-disseminated bony islands.
      - ii. The resultant weakening of the bone causes repeated microfractures leading to the classically described “shepherd’s crook” deformity.
    2. Histopathology:
      - i. Irregular woven bone described as having an “alphabet soup” or “Chinese letter” appearance.
      - ii. Unlike most benign tumors with osteoid matrix, fibrous dysplasia will have minimal or no osteoblastic rimming of the bone.
    3. Genetics:
      - i. The Gs alpha protein is a transmembrane cytokine signaling protein. Fibrous dysplasia is characterized by a mutation of chromosome 20q13 causing an activation of Gs alpha protein leading to an increased production of cyclic adenosine monophosphate (cAMP).
      - ii. The mutation will cause an increased production of fibroblast growth factor 23 (FGF-23), leading to renal wasting of phosphate.
  3. Treatment and prognosis:
    1. Asymptomatic lesions are treated with observation because the lesion will stop growing after the patient reaches skeletal maturity.
    2. Deformity or pathologic fractures of the proximal femur are treated with curettage, bone grafting, correction of the deformity, and internal fixation.
    3. Patients are considered to have a 1% risk of malignant transformation.
IV. Benign cartilage lesions:
1. Chondroblastoma ⁷ , ⁸ :
  1. Clinical presentation:
    1. Most patients presenting with a chondroblastoma will be younger than 25 years.
    2. Typically a patient will present with hip pain and limp, with the lesion being discovered during routine radiographs.
  2. Diagnostics:
    1. Radiographs:
      - i. Chondroblastoma is one of the characteristic lesions found in the epiphysis. Plain film radiographs will show a well-circumscribed lytic lesion.
      - ii. Frequently, the lesion will involve both epiphysis and metaphysis.
      - iii. In the proximal femur, the lesion can be located in either the capital epiphysis or the greater trochanter apophysis.
    2. Histopathology:
      - i. The lesions will have proliferating chondroblasts. The cells are classically described as having a “cobblestone” or “chicken wire” pattern.
      - ii. Giant cells will be scattered within the field of mononuclear chondroblasts.
  3. Treatment and prognosis:
    1. Symptomatic patients are treated with curettage and bone grafting.
    2. Despite the benign classification of the lesion, it is known to have pulmonary metastases that are treated with surgical resection.
2. Enchondroma ⁸ :
  1. Clinical presentation:
    1. A solitary enchondroma will typically be an incidental finding on plain film radiographs.
    2. The peak incidence of an enchondroma is during the third decade of life. Although the vast majority occurs in the hand, the most common location in a long bone is the proximal femur.
    3. Ollier’s disease is a nonheritable disease characterized by multiple intramedullary enchondroma lesions.
    4. Maffucci’s syndrome is a condition consisting of multiple enchondroma lesions with the presence of soft-tissue angiomas.
  2. Diagnostics:
    1. Radiographs:
      - i. Lesions will have variable patterns of calcifications often described as rings, stipples, or punctate, but these patterns will have a uniform distribution.
      - ii. Scalloping that involves more than 50% of the cortical width is a characteristic of malignant transformation to a chondrosarcoma.
      - iii. Enchondromas are classically observed as “hot” lesions on a bone scan.
    2. Histopathology:
      - i. These lesions will be hypocellular with an abundance of hyaline matrix.
  3. Treatment and prognosis:
    1. Observation is the mainstay of treatment with painful lesions necessitating curettage and bone grafting for concern of malignant transformation.
    2. A solitary enchondroma carries a 1% risk of malignant transformation.
    3. Approximately one-third of patients with Ollier’s disease will have malignant transformation to chondrosarcoma.
    4. All patients with Maffucci’s syndrome will have a malignant transformation to chondrosarcoma with risks of other visceral organ cancers.