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Bone Tumors MCQs

Practice Set 42 of 52

This practice set contains high-yield board review questions covering key concepts in Bone Tumors. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 821

Topic: Bone Tumors
Which of the following mutations is characteristic of McCune-Albright syndrome, a severe systemic form of fibrous dysplasia?
. EXT1 mutation
. GNAS1 mutation
. COL1A1 mutation
. FGFR3 mutation
. COMP mutation

Correct Answer & Explanation

. GNAS1 mutation

Explanation

McCune-Albright syndrome is caused by a somatic activating mutation in the GNAS1 gene, which leads to increased intracellular cAMP, affecting bone, skin (café-au-lait spots), and endocrine tissues.

Question 822

Topic: Bone Tumors

Radiographs of a 50-year-old man with knee pain show advanced joint space narrowing and multiple intra-articular calcified bodies of varying sizes. Histology shows chondroid nodules with mild cellular atypia. What is the most likely diagnosis?

. Primary synovial chondromatosis
. Secondary synovial chondromatosis
. Chondrosarcoma
. Gouty tophi
. Pigmented villonodular synovitis

Correct Answer & Explanation

. Secondary synovial chondromatosis

Explanation

Secondary synovial chondromatosis is associated with underlying joint pathology like advanced osteoarthritis. The loose bodies typically vary in size and number, unlike primary disease where they are numerous and uniform in size.

Question 823

Topic: Bone Tumors

A patient with cleidocranial dysplasia presents for orthopedic evaluation. Which of the following skeletal manifestations is most classically associated with this condition?

. Absence or hypoplasia of the clavicles
. Rhizomelic dwarfism
. Severe bowing of the tibiae
. Multiple osteochondromas
. Osteopoikilosis

Correct Answer & Explanation

. Absence or hypoplasia of the clavicles

Explanation

Cleidocranial dysplasia, caused by a RUNX2 (CBFA1) mutation, is characterized by absent or hypoplastic clavicles, delayed closure of cranial sutures, and dental abnormalities.

Question 824

Topic: Bone Tumors

On T2-weighted MRI, an aneurysmal bone cyst (ABC) is most reliably distinguished from a unicameral bone cyst (UBC) by the presence of which of the following?

. A thin, uniform sclerotic rim
. Fluid-fluid levels with multiple septations
. A purely radiolucent interior without septa
. Extensive perilesional edema
. Cortical thickening

Correct Answer & Explanation

. Fluid-fluid levels with multiple septations

Explanation

While both can occasionally show fluid levels, an ABC typically demonstrates multiple internal septations and distinct fluid-fluid levels on MRI due to the separation of serum and red blood cells in its cystic spaces.

Question 825

Topic: Bone Tumors

A 10-year-old boy presents with acute arm pain after throwing a baseball. Radiographs reveal a pathologic fracture through a centrally located proximal humerus radiolucent lesion. A small fragment of bone is seen resting at the dependent portion of the lesion. What is the diagnosis?

. Aneurysmal bone cyst
. Non-ossifying fibroma
. Unicameral bone cyst
. Enchondroma
. Chondroblastoma

Correct Answer & Explanation

. Unicameral bone cyst

Explanation

The "fallen leaf" or "fallen fragment" sign is pathognomonic for a pathologic fracture through a unicameral bone cyst (UBC). The cortical fragment breaks off and falls through the fluid-filled cyst to rest at the dependent portion.

Question 826

Topic: Bone Tumors

An 18-year-old male presents with chronic knee pain. Imaging reveals an eccentrically located, sharply marginated, lobulated radiolucent lesion in the proximal tibial metaphysis with a sclerotic rim. Histology shows stellate cells in a myxoid background with scattered osteoclast-like giant cells. What is the diagnosis?

. Aneurysmal bone cyst
. Chondromyxoid fibroma
. Chondroblastoma
. Unicameral bone cyst
. Giant cell tumor

Correct Answer & Explanation

. Chondromyxoid fibroma

Explanation

The clinical, radiographic (eccentric, lobulated metaphyseal lesion), and histologic (stellate cells in myxoid stroma) features are classic for chondromyxoid fibroma. Chondroblastoma would typically be an epiphyseal lesion.

Question 827

Topic: Bone Tumors

A 12-year-old boy presents with an eccentric, expansile lytic lesion in the proximal tibia. MRI reveals fluid-fluid levels. Biopsy confirms an Aneurysmal Bone Cyst (ABC). Which of the following genetic abnormalities is most characteristic of this primary lesion?

. GNAS mutation
. USP6 gene rearrangement
. COL2A1 mutation
. EXT1 mutation
. FGFR3 mutation

Correct Answer & Explanation

. USP6 gene rearrangement

Explanation

Primary Aneurysmal Bone Cysts are true neoplasms driven by a recurrent t(16;17) translocation resulting in a USP6 gene rearrangement. GNAS mutations are classically seen in fibrous dysplasia.

Question 828

Topic: Bone Tumors
A 25-year-old female presents with an expansile, ground-glass lesion in her proximal femur. She reports a history of precocious puberty and has large, irregular hyperpigmented macules on her back. What is the underlying mechanism of her orthopedic condition?
. Loss-of-function mutation in the NF1 gene
. Activating mutation of the GNAS gene
. Defective carbonic anhydrase II
. Overexpression of the RANKL protein
. Defect in type I collagen synthesis

Correct Answer & Explanation

. Activating mutation of the GNAS gene

Explanation

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, precocious puberty, and café-au-lait spots with "coast of Maine" borders. It is caused by a sporadic, post-zygotic activating mutation in the GNAS gene leading to increased intracellular cAMP.

Question 829

Topic: Bone Tumors

During surgical curettage of a suspected unicameral bone cyst (UBC) in the proximal humerus of a 10-year-old, the surgeon notes a thick membrane and profuse, pulsatile bleeding from the cavity. What is the most appropriate next step?

. Pack the defect with allograft chips
. Inject absolute alcohol into the cyst
. Obtain an intraoperative frozen section
. Perform wide en bloc resection
. Administer systemic tranexamic acid

Correct Answer & Explanation

. Obtain an intraoperative frozen section

Explanation

Profuse pulsatile bleeding and a thick fleshy membrane in a cystic lesion are characteristic of an Aneurysmal Bone Cyst (ABC) or a telangiectatic osteosarcoma, not a UBC. A frozen section is necessary to rule out malignancy before proceeding with definitive curettage or other treatments.

Question 830

Topic: Bone Tumors

A 9-year-old boy presents with sudden shoulder pain after throwing a baseball. Radiographs reveal a pathologic fracture through a centrally located, expansile radiolucent lesion in the proximal humerus metaphysis. A cortical fragment is seen resting at the dependent portion of the lesion. Which of the following is the most appropriate initial management?

. Immediate open curettage and bone grafting
. Aspiration and injection of methylprednisolone acetate
. Sling immobilization and observation for fracture healing
. En bloc resection and fibular strut allograft
. Percutaneous radiofrequency ablation

Correct Answer & Explanation

. Sling immobilization and observation for fracture healing

Explanation

The 'fallen leaf sign' is pathognomonic for a unicameral bone cyst (UBC). The initial management of a pathologic fracture through a UBC is immobilization to allow fracture healing, which may occasionally lead to spontaneous resolution of the cyst.

Question 831

Topic: Bone Tumors

A 22-year-old woman with known polyostotic fibrous dysplasia presents with progressive symptomatic varus deformity of her proximal femur (shepherd's crook deformity). Surgical reconstruction is planned. Which of the following bone grafting techniques is most appropriate for managing the resultant bony defects after corrective osteotomy?

. Autologous cancellous bone graft
. Allogeneic cancellous bone graft
. Cortical strut allograft
. Demineralized bone matrix with bone marrow aspirate
. Recombinant human BMP-2 on a collagen sponge

Correct Answer & Explanation

. Cortical strut allograft

Explanation

Cancellous bone grafts are rapidly resorbed and replaced by dysplastic woven bone in fibrous dysplasia. Cortical bone grafts are required as they resist resorption and provide necessary long-term structural support.

Question 832

Topic: Bone Tumors

A 9-year-old boy sustains mild trauma to his shoulder. Radiographs show a central, fully radiolucent, mildly expansile lesion in the proximal humeral metaphysis. A small cortical bone fragment is seen resting at the dependent portion of the cyst. What is this sign called?

. Bite sign
. Fallen leaf sign
. Target sign
. String sign
. Sunburst pattern

Correct Answer & Explanation

. Fallen leaf sign

Explanation

The "fallen leaf" or "fallen fragment" sign is pathognomonic for a unicameral bone cyst (UBC). It occurs when a fractured piece of cortical bone settles into the dependent portion of the fluid-filled cyst cavity.

Question 833

Topic: Bone Tumors

When interpreting advanced imaging for a suspected aneurysmal bone cyst (ABC) in the distal femur, which of the following MRI findings is highly characteristic, though not entirely pathognomonic?

. Solid, homogenous enhancement with gadolinium
. Target sign with a peripheral hyperintense rim
. Fluid-fluid levels on T2-weighted imaging
. Extensive flow voids indicating arteriovenous shunting
. Popcorn-like stippled calcifications

Correct Answer & Explanation

. Fluid-fluid levels on T2-weighted imaging

Explanation

Aneurysmal bone cysts typically show fluid-fluid levels on T2-weighted MRI, representing the sedimentation of blood products of varying ages. While characteristic of an ABC, this finding can also be seen in telangiectatic osteosarcoma.

Question 834

Topic: Bone Tumors

A 9-year-old female presents with multiple bony deformities and large cutaneous macules with irregular, jagged borders. She is also noted to have advanced bone age and early breast development. Which of the following is the most likely endocrine abnormality in this patient?

. Hyperparathyroidism
. Hypothyroidism
. Precocious puberty
. Diabetes insipidus
. Cushing's syndrome

Correct Answer & Explanation

. Precocious puberty

Explanation

This patient has McCune-Albright syndrome, which consists of the triad of polyostotic fibrous dysplasia, "Coast of Maine" cafe-au-lait spots, and endocrine abnormalities. Precocious puberty is the most common endocrine manifestation.

Question 835

Topic: Bone Tumors

To differentiate a simple (unicameral) bone cyst from an aneurysmal bone cyst on plain radiographs, the anatomic location within the host bone is a key feature. Which of the following locations is classic for an active unicameral bone cyst in a child?

. Eccentric in the metaphysis
. Central in the metaphysis adjacent to the physis
. Eccentric in the epiphysis
. Central in the diaphysis
. Intracortical in the diaphysis

Correct Answer & Explanation

. Central in the metaphysis adjacent to the physis

Explanation

Unicameral (simple) bone cysts are classically located centrally within the metaphysis immediately adjacent to the physis in growing children. Aneurysmal bone cysts, by contrast, are characteristically eccentric and expansile.

Question 836

Topic: Bone Tumors

A 25-year-old female presents with multiple expansile "ground glass" bone lesions, cafe-au-lait spots with irregular borders, and a history of precocious puberty. This condition is caused by a somatic activating mutation in which of the following?

. EXT1 gene
. GNAS1 gene
. COMP gene
. FGFR3 gene
. COL1A1 gene

Correct Answer & Explanation

. GNAS1 gene

Explanation

McCune-Albright syndrome is characterized by polyostotic fibrous dysplasia, cafe-au-lait spots with irregular borders, and endocrine abnormalities. It is caused by a somatic post-zygotic activating mutation in the GNAS1 gene, which encodes the alpha subunit of the stimulatory G protein.

Question 837

Topic: Bone Tumors

A 32-year-old male with polyostotic fibrous dysplasia presents with increasing thigh pain and a progressive "shepherd's crook" deformity of his proximal femur. What is the most appropriate surgical management?

. Curettage and bone grafting with allograft
. Curettage and bone grafting with autograft
. Valgus-producing osteotomy and locked plating
. Corrective osteotomy and intramedullary nailing
. Amputation

Correct Answer & Explanation

. Corrective osteotomy and intramedullary nailing

Explanation

Deformities in fibrous dysplasia, such as the shepherd's crook deformity, are best managed with corrective osteotomies and load-sharing devices like intramedullary nails. Bone grafting is generally ineffective because the graft undergoes resorption and replacement by dysplastic bone.

Question 838

Topic: Bone Tumors

A 6-year-old boy presents with an asymmetric, painless overgrowth on the medial aspect of his right ankle. Radiographs show an irregular, lobulated mass arising from the medial epiphysis of the distal tibia. What is the most likely diagnosis?

. Multiple hereditary exostoses
. Synovial chondromatosis
. Dysplasia epiphysealis hemimelica (Trevor disease)
. Ollier disease
. Maffucci syndrome

Correct Answer & Explanation

. Dysplasia epiphysealis hemimelica (Trevor disease)

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is an asymmetrical, focal overgrowth of cartilage resembling an osteochondroma but arising from the epiphysis. It most commonly affects the medial side of the lower extremity joints, particularly the ankle and knee.

Question 839

Topic: Bone Tumors

A 14-year-old girl with polyostotic fibrous dysplasia presents with increasing groin and thigh pain. Radiographs demonstrate a progressive shepherd's crook deformity of the proximal femur with an impending fracture. What is the most appropriate surgical management?

. Curettage and cancellous bone grafting of the lesion
. Valgus-producing proximal femoral osteotomy with intramedullary nailing
. Varus-producing proximal femoral osteotomy with blade plate fixation
. Prophylactic external beam radiation therapy
. Observation in a hip spica cast

Correct Answer & Explanation

. Valgus-producing proximal femoral osteotomy with intramedullary nailing

Explanation

The shepherd's crook deformity in fibrous dysplasia leads to high mechanical stress on the proximal femur. Treatment requires a valgus-producing osteotomy to correct the mechanical axis, combined with intramedullary nailing spanning the entire bone to prevent stress risers and future fractures.

Question 840

Topic: Bone Tumors
A 6-year-old girl is evaluated for a limp, precocious puberty, and large café-au-lait spots with irregular 'coast of Maine' borders. Pelvic radiographs show a bubbly, expansile lesion in the proximal femur with a ground-glass matrix. The somatic mosaic mutation responsible for this syndrome causes hyperactivation of which pathway?
. cAMP secondary messenger system (G-protein)
. Fibroblast growth factor receptor 3
. Cartilage oligomeric matrix protein
. Membrane sulfate transporter
. Wnt/beta-catenin signaling

Correct Answer & Explanation

. cAMP secondary messenger system (G-protein)

Explanation

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, precocious puberty, and café-au-lait spots. It is caused by a somatic mutation in the GNAS gene, which leads to constitutive activation of the Gs-alpha protein and continuous cAMP production.

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