LE5-6 (Neuro/MSK) 2026 Flashcards

Question

25. Which lobe is most commonly affected by otomastoiditis? A. Parietal lobe B. Frontal lobe C. Occipital lobe D. Temporal lobe

Answer 1

D. Temporal lobe Rationale: Otomastoiditis can spread to the temporal lobe via direct extension or venous drainage pathways, leading to temporal lobe abscesses.

Answer 2

D. Early cerebritis Rationale: In the early cerebritis stage, CT scans may be normal or show a low-density area due to initial infection and inflammation.

Answer 3

C. Late cerebritis Rationale: Late cerebritis is characterized by thick, irregular contrast enhancement at the lesion edges, indicating necrosis and inflammation.

Answer 4

B. Early capsule Rationale: Early capsule formation occurs when the immune response walls off the infection, and CT/MRI show a well-defined rim of enhancemen

Answer 5

A. Late capsule Rationale: In the late capsule stage, the rim of enhancement becomes thinner and better defined, indicating a mature abscess wall with reduced inflammation.

Answer 6

A. Target appearance Rationale: Tuberculomas can show a "target appearance" on imaging, characterized by a central area of necrosis, surrounded by an enhancing rim.

Answer 7

D. Small with solid or thick rim enhancement Rationale: Most fungal granulomas appear as small lesions with solid or thick rim enhancement on imaging, reflecting chronic inflammation and necrosis.

Answer 8

B. Cryptococcosis Rationale: Cryptococcus neoformans is the most frequently reported CNS fungal infection, particularly in immunocompromised patients (e.g., AIDS), often presenting with gelatinous pseudocysts and basal meningeal enhancement.

Answer 9

C. Scolex Rationale: In cysticercosis, the scolex is the small nodular structure within the cyst, representing the head of the parasite, and it enhances with contrast.

Answer 10

B. Large solitary unilocular cyst Rationale: Echinococcosis (hydatid disease) is characterized by a large, unilocular cyst with a well-defined wall, typically affecting the liver and brain.

Answer 11

A. Congenital cytomegalovirus Rationale: Congenital CMV infection classically causes multiple periventricular calcifications, leading to neurodevelopmental abnormalities.

Answer 12

B. Herpes simplex encephalitis Rationale: Herpes simplex virus (HSV-1) preferentially affects the temporal lobes, causing necrotizing encephalitis with edema and hemorrhage on imaging.

Answer 13

C. Marked contrast enhancement near the base of the brain and basal cisterns Rationale: Tuberculous meningitis typically presents with enhancement of the basal meninges and cisterns, along with hydrocephalus and infarcts.

Answer 14

C. A mass lesion is presumed whenever there is a shift in midline structures Rationale: Midline shift on imaging is a key indicator of mass effect, which suggests the presence of a tumor, hematoma, or large infarct.

Answer 15

B. Glioma Rationale: Intra-axial masses originate within the brain parenchyma, and gliomas are primary brain tumors arising from glial cells.

Answer 16

D. Meningioma Rationale: Extra-axial masses originate outside the brain parenchyma, and meningiomas arise from the meninges, making them extra-axial.

Answer 17

B. Glioblastoma multiforme Rationale: Glioblastoma multiforme (GBM) is highly invasive and spreads through the corpus callosum, forming a "butterfly glioma" appearance.

Answer 18

B. Glioblastoma multiforme Rationale: Although GBM affects large brain volumes, true multicentric tumors (independent origins) are rare in GBM but more common in metastases.

Answer 19

B. Low-grade astrocytoma Rationale: Low-grade astrocytomas, especially pilocytic astrocytomas, frequently present with cystic components with an enhancing mural nodule.

Answer 20

B. Meningioma Rationale: Meningiomas parasitize the vasculature of adjacent brain tissue, showing a characteristic "dural tail sign" on angiography.

Answer 21

B. Ependymoma Rationale: Ependymomas arise from ependymal cells, which line the ventricles, commonly occurring near the lateral or fourth ventricle.

Answer 22

A. Craniopharyngioma Rationale: Craniopharyngiomas originate from Rathke’s pouch remnants, typically found in the suprasellar region.

Answer 23

C. Pituitary adenoma Rationale: Pituitary adenomas grow within the sella turcica and can erode its floor, particularly in macroadenomas.

Answer 24

B. Metastasis Rationale: Metastatic tumors frequently lodge in the gray-white matter junction due to embolization and abrupt vascular caliber changes.

Answer 25

A. Acoustic schwannoma Rationale: Acoustic (vestibular) schwannomas arise in the cerebellopontine angle, often displacing the fourth ventricle.

Answer 26

A. Pituitary microadenoma Rationale: Prolactin-secreting pituitary microadenomas cause hyperprolactinemia, leading to amenorrhea and galactorrhea.

Answer 27

A. Narrow zone of transition Rationale: A narrow zone of transition with well-defined borders is characteristic of benign bone lesions, whereas a wide zone indicates aggressive or malignant processes.

Answer 28

C. Expansile Rationale: Expansile lesions grow outward but maintain cortical integrity, as seen in Aneurysmal Bone Cysts and Osteoblastomas.

Answer 29

B. Monostotic form Rationale: Monostotic Fibrous Dysplasia accounts for about 85% of cases, affecting a single bone, whereas the polyostotic form is less common.

Answer 30

D. No periosteal reaction Rationale: Fibrous Dysplasia is a benign lesion that does not induce a periosteal reaction, making this a key distinguishing feature.

Answer 31

C. Phalanges Rationale: Enchondromas in the phalanges occur without soft tissue hemangiomas, distinguishing them from syndromes like Maffucci Syndrome.

Answer 32

A. Ollier Disease Rationale: Ollier Disease consists of multiple enchondromas but lacks the soft tissue hemangiomas seen in Maffucci Syndrome.

Answer 33

B. Maffucci Syndrome Rationale: Maffucci Syndrome presents with multiple enchondromas and soft tissue hemangiomas, distinguishing it from Ollier Disease, which lacks hemangiomas.

Answer 34

B. Must be less than 30 years of age Rationale: Eosinophilic Granuloma, a form of Langerhans Cell Histiocytosis, primarily affects children and young adults under 30 years old.

Answer 35

A. Epiphyses must be open Rationale: Giant Cell Tumors typically occur after physeal closure, meaning the epiphyses must be closed, not open.

Answer 36

D. Non-Ossifying Fibroma Rationale: A fibrous cortical defect that exceeds 2 cm is classified as a Non-Ossifying Fibroma, a benign lesion commonly found in children and adolescents.

Answer 37

D. Osteoblastoma Rationale: Osteoblastomas often occur in the posterior elements of the spine and are frequently associated with Aneurysmal Bone Cysts.

Answer 38

D. Both A and B (Metastases and Multiple Myeloma) Rationale: Metastatic bone disease and Multiple Myeloma are the most common bone malignancies in older adults.

Answer 39

C. Fallen Fragment Sign Rationale: The "Fallen Fragment Sign" is highly characteristic of a Solitary Bone Cyst after a pathological fracture.

Answer 40

C. Infection Rationale: Infection, particularly osteomyelitis, must always be considered in the differential diagnosis of a lucent or cystic bone lesion.

Answer 41

A. Metastasis Rationale: Metastatic bone lesions are rare in individuals under 30 unless there is a known primary malignancy.

Answer 42

A. Osteophytosis, Sclerosis, and Joint space narrowing Rationale: The radiologic hallmarks of osteoarthritis (OA) include: Osteophytosis → Formation of bone spurs (osteophytes) at joint margins due to cartilage degeneration. Subchondral Sclerosis → Increased bone density in areas subjected to stress. Joint Space Narrowing → Loss of cartilage leads to reduced joint space, commonly seen in weight-bearing joints.

Answer 43

C. Osteoarthritis Rationale: Intra-articular fractures disrupt joint surfaces, leading to cartilage damage and subsequent post-traumatic osteoarthritis due to abnormal joint mechanics and wear.

Answer 44

C. Bilateral, Osteopenia, Soft tissue swelling, and Joint space narrowing Rationale: Rheumatoid arthritis (RA) is a bilateral, inflammatory arthritis characterized by: Osteopenia (periarticular bone loss due to inflammation). Soft tissue swelling from synovitis. Joint space narrowing due to cartilage destruction. Erosions and joint deformities in advanced cases.

Answer 45

D. Tophi Rationale: Tophi are pathognomonic for chronic gout, representing deposits of monosodium urate crystals in soft tissues. They appear as soft tissue masses with possible calcifications on X-ray.

Answer 46

B. Rheumatoid arthritis Rationale: Protrusio acetabuli refers to medial displacement of the femoral head into the pelvis due to progressive joint destruction, commonly seen in RA, osteomalacia, and Paget’s disease.

Answer 47

B. Bilateral and Symmetrical Rationale: Ankylosing spondylitis (AS) classically presents with bilateral, symmetrical sacroiliitis, with erosions, sclerosis, and eventual fusion of the sacroiliac joints, seen as the “bamboo spine” appearance on X-ray.

Answer 48

C. Overhanging edges Rationale: Gouty erosions are well-defined, punched-out lesions with sclerotic margins and overhanging edges ("rat bite" erosions). They are typically juxta-articular but sparing the joint space.

Answer 49

C. Psoriatic arthritis Rationale: The pencil-in-cup deformity occurs due to progressive bone resorption leading to tapering of the proximal phalanx and cupping of the adjacent bone. It is a hallmark of psoriatic arthritis.

Answer 50

B. Ankylosing spondylitis Rationale: Bamboo spine refers to fusion of vertebrae due to syndesmophytes, leading to a rigid spine appearance on X-ray. This is a classic finding in ankylosing spondylitis.

Answer 51

A. Extension of the distal interphalangeal joint and flexion of the proximal interphalangeal joint Rationale: Boutonniere deformity occurs due to injury or chronic inflammatory conditions like rheumatoid arthritis, leading to PIP flexion and DIP hyperextension due to central slip tendon disruption. B. Extension of the PIP and flexion of the DIP → Incorrect (this describes Swan-neck deformity, seen in rheumatoid arthritis).

Answer 52

A. Nasal bone Rationale: The nasal bone is the most frequently fractured facial bone due to its prominence and exposure to trauma.

Answer 53

B. MRI Rationale: MRI is the best imaging modality for ligamentous injuries because it provides high-resolution soft tissue contrast, allowing detailed visualization of ligaments, tendons, and cartilage.

Answer 54

D. Parachute reflex Rationale: The parachute reflex is a protective reflex that appears around 6-9 months and never disappears. When a baby is suddenly moved downward, they extend their arms to brace for impact, similar to how adults extend their hands in a FOOSH injury.

Answer 55

B. Osteoarthritis Rationale: Osteoarthritis (OA) is the most common type of arthritis, affecting millions worldwide, particularly in older adults. It results from cartilage degeneration, leading to joint space narrowing, osteophytes, and sclerosis.

Answer 56

A. Skeletal series radiographs Rationale: X-ray (Skeletal radiographs) is the first-line imaging for suspected fractures in trauma patients due to availability, speed, and cost-effectiveness. CT is used for complex fractures (e.g., spine, pelvis, facial bones). MRI is used for soft tissue and occult fractures. DEXA is for osteoporosis, not acute trauma.

Answer 57

A. Eosinophilic granuloma Rationale: Eosinophilic granuloma (EG) is a benign bone lesion that is part of Langerhans Cell Histiocytosis (LCH). On X-ray, it can present as a lytic, aggressive-appearing lesion with cortical destruction, sometimes mimicking malignant bone tumors like Ewing’s sarcoma or osteosarcoma.

Answer 58

C. Zone of transition Rationale: A narrow zone of transition suggests a benign lesion, while a wide, ill-defined zone suggests an aggressive or malignant process. Malignant lesions often lack clear demarcation from normal bone due to rapid invasion.

Answer 59

A. Low-grade chronic irritation Rationale: Benign periosteal reactions occur due to slow-growing lesions, allowing the periosteum time to lay down new bone in an organized manner. This results in solid, thick, and well-defined periosteal reactions, commonly seen in osteoid osteoma and healing fractures.

Answer 60

C. Lamellated ("onion skin" appearance) Rationale: Malignant bone lesions (e.g., Ewing sarcoma, osteosarcoma) cause rapid, disrupted periosteal reactions, leading to: Lamellated (onion skin) → Repeated periosteal lifting. Spiculated (sunburst pattern) → Perpendicular new bone formation. Codman triangle → Periosteal elevation without full ossification.

Answer 61

B. Benign processes Rationale: Benign bone lesions show a well-defined, narrow transition from normal to abnormal bone. Malignant lesions or infections have a wide, poorly defined transition due to rapid growth and invasion.

Answer 62

D. Osteosarcoma is the most common primary malignant bone tumor.

Answer 63

B. Ewing sarcoma Rationale: Ewing sarcoma occurs in young patients (10-30 years old) and commonly affects the diaphysis/metaphysis of long bones. Presents with aggressive periosteal reactions (onion skin), lytic lesions, and soft tissue mass.

Answer 64

B. Myeloma Rationale: Multiple myeloma is the most common primary malignant bone tumor in adults over 50 years old, typically affecting those >60 years old. It presents with osteolytic ("punched-out") lesions, bone pain, and pathological fractures, commonly in the vertebrae, skull, ribs, and pelvis.

Answer 65

B. Has a second peak incidence in the sixth decade of life. Correct Diagnosis: Osteosarcoma Osteosarcoma is a highly aggressive malignant bone tumor that most commonly affects adolescents (10-25 years old). It presents with a "sunburst" periosteal reaction due to rapid bone formation. Second peak incidence occurs in older adults (~60s), often secondary to Paget’s disease, prior radiation, or chronic bone conditions.

Answer 66

A. Grows outside the bone. Rationale: Parosteal osteosarcoma is a low-grade variant of osteosarcoma that grows on the surface of the bone rather than inside the medullary cavity.

Answer 67

B. Eosinophilic granuloma is a differential diagnosis. Rationale: Ewing’s sarcoma is the most likely diagnosis in a young adult with a permeative lesion and onion-skin periosteal reaction.

Answer 68

B. Ewing’s sarcoma

Answer 69

A. Chondrosarcoma Rationale: Chondrosarcoma produces a cartilaginous matrix, seen as "snowflake" or "popcorn" calcifications on X-ray.

Answer 70

B. Can have a bony sequestrum completely separated from the surrounding bone. Rationale: Fibrosarcoma is an aggressive mesenchymal tumor that can produce a bony sequestrum due to cortical destruction.

Answer 71

C. Primary lymphoma of the bone Rationale: Primary lymphoma of the bone can be extensive yet asymptomatic for a long time. It presents as diffuse osteolysis without periosteal reaction and can involve multiple bones without systemic symptoms.

Answer 72

C. Renal cell carcinoma Rationale: Renal cell carcinoma (RCC) metastases are purely lytic.

Answer 73

A. Myeloma Rationale: Multiple myeloma is often cold on bone scans because it does not trigger an osteoblastic response.

Answer 74

D. Leads to multiple calcific loose bodies in a joint. Rationale: Synovial osteochondromatosis is a benign joint disorder causing cartilage metaplasia, leading to multiple loose bodies in the joint space.

Answer 75

D. Never has calcifications.

Answer 76

C. Fibrosarcoma Rationale: Fibrosarcoma is an aggressive malignant bone tumor that causes extensive cortical destruction, often appearing as a moth-eaten or permeative lesion.