KMU Past Paper Practice

Question:

A 15-year-old boy presents with a painful swelling of the proximal tibia. Radiography shows a mixed lytic and sclerotic metaphyseal mass. Histology reveals highly atypical spindle cells associated with irregular osteoid. Which tumour category best describes this lesion?

Options:

Correct Answer: Malignant bone-forming tumour

Explanation: Atypical malignant cells producing osteoid classify the lesion as osteosarcoma, a malignant bone-forming tumour.

Question:

A 17-year-old boy with suspected osteosarcoma undergoes examination of the affected distal femur. Which additional clinical finding would most directly indicate local structural weakening by the tumour?

Options:

Correct Answer: Fracture after minor trauma

Explanation: Tumour-induced cortical destruction weakens bone and may produce a pathological fracture after minimal trauma.

Question:

A bone tumour specimen from the distal femur is grey-white, gritty and variegated with areas of hemorrhage and necrosis. Which diagnosis best fits this gross appearance in an adolescent?

Options:

Correct Answer: Osteosarcoma

Explanation: A bulky gritty metaphyseal mass with hemorrhage and necrosis is characteristic of an aggressive osteoid-producing malignancy.

Question:

A 68-year-old man with Paget disease develops a rapidly enlarging painful mass in the femur. Which primary bone malignancy should be considered first?

Options:

Correct Answer: Osteosarcoma

Explanation: Osteosarcoma in older adults may arise secondarily in abnormal bone, including bone affected by Paget disease.

Question:

A 21-year-old man has a painful expansile lesion in the posterior element of a cervical vertebra. Which radiological characteristic would favour osteoblastoma over osteoid osteoma?

Options:

Correct Answer: A larger expansile osteoid-forming mass

Explanation: Osteoblastoma is generally larger and more expansile, whereas osteoid osteoma forms a small nidus with prominent reactive sclerosis.

Question:

A pathologist reviews two benign osteoid-forming lesions. Both contain woven bone rimmed by osteoblasts in vascular stroma. Which feature is most useful for distinguishing them?

Options:

Correct Answer: Lesion size and anatomical site

Explanation: Osteoid osteoma and osteoblastoma overlap histologically; size, site and clinical behaviour provide the decisive distinction.

Question:

A 14-year-old girl has pain and restricted movement of the knee. Imaging shows a small well-defined epiphyseal lesion. Which tumour should be prioritized in the differential diagnosis before growth-plate closure?

Options:

Correct Answer: Chondroblastoma

Explanation: Chondroblastoma characteristically arises in the epiphysis of adolescents and young adults, frequently producing joint symptoms.

Question:

A 23-year-old man has a metaphyseal lesion composed of lobules containing chondroid, myxoid and fibrous tissue. Which diagnosis is most likely?

Options:

Correct Answer: Chondromyxoid fibroma

Explanation: A lobulated metaphyseal lesion with mixed chondroid, myxoid and fibrous areas is typical of chondromyxoid fibroma.

Question:

A 45-year-old woman presents with deep pelvic pain. Imaging reveals a lobulated cartilage-producing mass. Which anatomical distribution is most compatible with chondrosarcoma?

Options:

Correct Answer: Pelvis and proximal long bones

Explanation: Chondrosarcoma mainly affects adults and commonly involves the pelvis, shoulder girdle, ribs and proximal long bones.

Question:

A cartilage-producing tumour shows increased cellularity, nuclear atypia and entrapment of pre-existing trabeculae. Which interpretation is most appropriate?

Options:

Correct Answer: Malignant cartilaginous neoplasm

Explanation: Permeative growth with entrapment of native bone and cytological atypia supports chondrosarcoma rather than a benign cartilage lesion.

Question:

A 12-year-old boy has persistent femoral pain and swelling with fever. Imaging shows an aggressive shaft lesion. Histology reveals small round cells. Which finding would best distinguish Ewing sarcoma from osteomyelitis?

Options:

Correct Answer: Clonal gene-fusion abnormality

Explanation: Inflammatory features overlap with infection, but a characteristic EWSR1-related fusion confirms a neoplastic small round-cell process.

Question:

A destructive femoral tumour in a child forms a large soft-tissue mass despite relatively limited external cortical change on one radiographic view. Which explanation best accounts for this finding?

Options:

Correct Answer: Medullary spread may precede obvious cortical destruction

Explanation: Aggressive marrow tumours can extend longitudinally and through small cortical breaches, creating a large soft-tissue component.

Question:

A 31-year-old woman has a locally aggressive epiphyseal lesion. Histology shows numerous giant cells whose nuclei resemble those of surrounding stromal cells. Which microscopic distribution is most characteristic?

Options:

Correct Answer: Giant cells evenly dispersed in the lesion

Explanation: Giant-cell tumour shows relatively uniform distribution of osteoclast-type giant cells among mononuclear stromal cells.

Question:

A giant-cell tumour is treated locally and later reappears at the same site. Which biological property best explains this outcome?

Options:

Correct Answer: Infiltrative local growth

Explanation: Giant-cell tumour is locally aggressive and may recur when microscopic extensions remain after local treatment.

Question:

A metaphyseal fibrous lesion in a child shows spindle fibroblasts in a storiform arrangement with histiocytes, foam cells and scattered giant cells. Which diagnosis is most likely?

Options:

Correct Answer: Non-ossifying fibroma

Explanation: Storiform fibroblasts with histiocytes, foam cells and scattered giant cells support a fibrous cortical defect or non-ossifying fibroma.

Question:

A fibrous cortical defect becomes smaller during follow-up as a child approaches skeletal maturity. Which mechanism best explains this change?

Options:

Correct Answer: Spontaneous replacement by normal bone

Explanation: Fibrous cortical defects are developmental lesions that commonly regress as the fibrous tissue is replaced during normal skeletal growth.

Question:

A radiograph shows a well-defined lesion with a narrow transition zone, an intact but thinned cortex and no soft-tissue mass. Which biological behaviour is most likely?

Options:

Correct Answer: Slow-growing localized lesion

Explanation: A narrow transition zone and smooth cortical remodeling indicate that surrounding bone has had time to respond to slow growth.

Question:

A suspected cartilage tumour contains mineralized matrix, but the plain radiograph does not clearly show the cortical details. Which imaging modality would best demonstrate mineralization and cortical architecture?

Options:

Correct Answer: Computed tomography

Explanation: CT is particularly useful for defining cortical destruction and mineralized osteoid or chondroid matrix.

Question:

An orthopedic team has completed plain radiography and MRI of an aggressive femoral lesion. Which step provides the definitive classification needed before tumour-specific treatment?

Options:

Correct Answer: Planned tissue biopsy

Explanation: Imaging characterizes and stages the lesion, but histopathological examination of a properly planned biopsy establishes the definitive diagnosis.

Question:

A 19-year-old man presents with a painful enlarging bone mass. Radiography reveals a wide transition zone, cortical breach and an extraosseous component. Which combination of findings most strongly indicates malignant biological behaviour?

Options:

Correct Answer: Cortical destruction and soft-tissue extension

Explanation: Breach of the cortex with extension beyond bone indicates rapid infiltrative growth and strongly supports an aggressive malignant process.