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10. Pathology and Oncology MCQs

Practice Set 351 of 351

This practice set contains high-yield board review questions covering key concepts in 10. Pathology and Oncology. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 7001

Topic: Bone Tumors
An asymptomatic 28-year-old male undergoes a pelvic radiograph following a minor trauma, revealing numerous small, well-defined, symmetric sclerotic foci clustered around the periarticular regions of the pelvis and proximal femurs. If this patient has an associated syndromic presentation, which of the following clinical findings is most likely to be present?
. Café-au-lait spots with smooth borders.
. Subcutaneous hemangiomas.
. Disseminated connective tissue nevi (elastomas).
. Unilateral renal agenesis.
. Blue sclerae.

Correct Answer & Explanation

. Disseminated connective tissue nevi (elastomas).

Explanation

The radiographic description of numerous small, symmetric, periarticular sclerotic foci is pathognomonic for Osteopoikilosis ('spotted bone disease'). It is an autosomal dominant condition often caused by mutations in the LEMD3 gene. While usually asymptomatic and an incidental finding, it can be associated with Buschke-Ollendorff syndrome. This syndrome is characterized by the combination of osteopoikilosis and disseminated connective tissue nevi (elastomas or collagenomas) in the skin. Café-au-lait spots are seen in NF1 and McCune-Albright. Hemangiomas are seen in Maffucci syndrome. Blue sclerae are classic for Osteogenesis Imperfecta.

Question 7002

Topic: Bone Tumors

A 9-year-old girl is diagnosed with Ollier disease after presenting with multiple asymmetric cartilaginous masses in her metaphyseal regions, causing limb length discrepancy. Somatic mosaic mutations in which of the following genes are most strongly implicated in the pathogenesis of her condition?

. EXT1
. GNAS
. IDH1
. LEMD3
. COMP

Correct Answer & Explanation

. IDH1

Explanation

Correct Answer: IDH1Ollier disease (multiple enchondromatosis) is a non-hereditary disorder characterized by multiple enchondromas, typically presenting with asymmetric limb involvement and deformities. It is caused by somatic mosaic mutations in the Isocitrate Dehydrogenase 1 (IDH1) or IDH2 genes. These mutations lead to the accumulation of the oncometabolite D-2-hydroxyglutarate, which interferes with normal chondrocyte differentiation. EXT1 is associated with Multiple Hereditary Exostoses. GNAS is associated with Fibrous Dysplasia. LEMD3 is associated with Osteopoikilosis and Melorheostosis. COMP is associated with Pseudoachondroplasia.

Question 7003

Topic: 10. Pathology and Oncology

A 32-year-old male with a known history of multiple hereditary exostoses presents with new-onset pain and swelling over a long-standing lesion on his proximal medial tibia. Which of the following MRI findings is most highly suspicious for secondary malignant transformation to chondrosarcoma?

. A cartilage cap thickness of 0.5 cm.
. Continuity of the lesion's medullary cavity with the host bone.
. A cartilage cap thickness of 2.5 cm.
. Presence of a bursa overlying the osteochondroma.
. Sclerotic margins at the base of the stalk.

Correct Answer & Explanation

. A cartilage cap thickness of 2.5 cm.

Explanation

Correct Answer: A cartilage cap thickness of 2.5 cm.Patients with Multiple Hereditary Exostoses (MHE) have a 1-5% lifetime risk of malignant transformation of an osteochondroma into a secondary chondrosarcoma. Clinical signs include new-onset pain, growth of the lesion after skeletal maturity, and a new soft tissue mass. On MRI, the most reliable indicator of malignant transformation is the thickness of the cartilage cap. A cartilage cap thicker than 1.5 to 2.0 cm in an adult is highly suspicious for chondrosarcoma and warrants biopsy or wide resection. Continuity of the medullary cavity is a defining feature of a benign osteochondroma, not a sign of malignancy. An overlying bursa (exostosis bursa) is a common benign cause of pain and swelling.

Question 7004

Topic: 10. Pathology and Oncology
A 45-year-old female with known polyostotic fibrous dysplasia presents with a slowly enlarging, painless, deep-seated soft tissue mass in her right thigh. MRI reveals a well-circumscribed, intramuscular mass with high T2 signal intensity. Biopsy confirms a benign myxoma. This combination of findings is pathognomonic for which of the following syndromes?
. McCune-Albright syndrome
. Maffucci syndrome
. Mazabraud syndrome
. Buschke-Ollendorff syndrome
. Jaffe-Campanacci syndrome

Correct Answer & Explanation

. Mazabraud syndrome

Explanation

Mazabraud syndrome is a rare disorder characterized by the association of fibrous dysplasia (usually polyostotic) with one or more intramuscular myxomas. The myxomas typically occur in the same anatomic region as the most severe bone lesions. Recognizing this syndrome is important because patients with Mazabraud syndrome have a slightly higher risk of malignant transformation of their fibrous dysplasia lesions compared to those with isolated fibrous dysplasia. McCune-Albright syndrome involves fibrous dysplasia, café-au-lait spots, and endocrinopathies. Maffucci syndrome involves enchondromas and hemangiomas. Buschke-Ollendorff involves osteopoikilosis and connective tissue nevi. Jaffe-Campanacci syndrome involves non-ossifying fibromas and café-au-lait spots.

Question 7005

Topic: Bone Tumors
A 12-year-old girl presents with a progressive 'shepherd's crook' deformity of the proximal femur. Radiographs show a characteristic ground-glass appearance of the medullary canal with cortical thinning. Physical examination reveals café-au-lait spots with irregular, 'coast of Maine' borders, and her pediatrician notes a history of precocious puberty. Which of the following best describes the underlying molecular pathogenesis of this patient's condition?
. Mutation in the EXT1 gene leading to abnormal heparan sulfate synthesis.
. Activating mutation in the GNAS1 gene leading to increased intracellular cAMP.
. Mutation in the FGFR3 gene causing constitutive activation of the receptor.
. Defect in the COL1A1 gene leading to abnormal type I collagen synthesis.
. Mutation in the COMP gene affecting cartilage oligomeric matrix protein.

Correct Answer & Explanation

. Activating mutation in the GNAS1 gene leading to increased intracellular cAMP.

Explanation

This patient presents with McCune-Albright syndrome, a severe form of polyostotic fibrous dysplasia associated with endocrinopathies (most commonly precocious puberty) and characteristic café-au-lait spots with irregular borders. The underlying cause of fibrous dysplasia is a somatic, activating mutation in the GNAS1 gene. This mutation leads to a constitutively active Gs-alpha protein, resulting in the overproduction of intracellular cyclic AMP (cAMP). This overproduction disrupts normal osteoblast differentiation, leading to the replacement of normal bone with anarchic, immature fibrous tissue and woven bone. EXT1 mutations cause Multiple Hereditary Exostoses. FGFR3 mutations cause Achondroplasia. COL1A1 defects cause Osteogenesis Imperfecta. COMP mutations cause Pseudoachondroplasia or Multiple Epiphyseal Dysplasia.

Question 7006

Topic: 10. Pathology and Oncology

A 25-year-old male with a known history of multiple hereditary exostoses (diaphyseal aclasis) presents with a rapidly enlarging, painful mass over his right proximal humerus. Radiographs show a previously stable osteochondroma that now exhibits a thickened cartilage cap and irregular, flocculent calcifications in the surrounding soft tissue. What is the most likely diagnosis, and what is the estimated lifetime risk of this complication in patients with his underlying syndrome?

. Osteosarcoma; 1-2%
. Secondary chondrosarcoma; 1-5%
. Secondary chondrosarcoma; 20-25%
. Fibrosarcoma; 5-10%
. Malignant peripheral nerve sheath tumor; 10-15%

Correct Answer & Explanation

. Secondary chondrosarcoma; 1-5%

Explanation

Correct Answer: Secondary chondrosarcoma; 1-5%Multiple hereditary exostoses (MHE) is an autosomal dominant skeletal dysplasia characterized by the anarchic development of multiple osteochondromas. The most feared complication is malignant transformation into a secondary chondrosarcoma. Clinical signs of malignant transformation include new onset of pain, rapid growth of a previously stable lesion after skeletal maturity, and a cartilage cap thickness greater than 1.5 to 2 cm on MRI. The lifetime risk of malignant transformation in patients with MHE is generally estimated to be between 1% and 5% in modern literature (though older texts sometimes cited higher rates up to 10%). Osteosarcoma and fibrosarcoma are not the typical malignancies arising from osteochondromas.

Question 7007

Topic: 10. Pathology and Oncology

A 14-year-old boy presents with multiple asymmetric cartilaginous lesions in the metaphyses and diaphyses of his hands, femur, and tibia, causing significant deformity. Physical examination reveals multiple soft tissue hemangiomas with phleboliths noted on plain radiographs. Which of the following is true regarding this patient's condition compared to a patient with isolated multiple enchondromatosis (Ollier disease)?

. The condition is inherited in an autosomal dominant pattern.
. There is a lower risk of malignant transformation to chondrosarcoma.
. The patient has a significantly higher risk of developing visceral malignancies, such as astrocytoma or gastrointestinal tract carcinomas.
. The skeletal lesions typically resolve spontaneously after skeletal maturity.
. The primary genetic defect involves the GNAS1 gene.

Correct Answer & Explanation

. The patient has a significantly higher risk of developing visceral malignancies, such as astrocytoma or gastrointestinal tract carcinomas.

Explanation

Correct Answer: The patient has a significantly higher risk of developing visceral malignancies, such as astrocytoma or gastrointestinal tract carcinomas.The patient has Maffucci syndrome, characterized by multiple enchondromas associated with soft tissue hemangiomas. Both Ollier disease and Maffucci syndrome are non-hereditary (somatic mosaicism, often involving IDH1 or IDH2 mutations, not GNAS1). While both carry a high risk of malignant transformation to chondrosarcoma (higher in Maffucci than Ollier), Maffucci syndrome is uniquely associated with a significantly increased risk of visceral malignancies, including astrocytomas, gastrointestinal carcinomas, and ovarian tumors. The skeletal lesions do not resolve spontaneously; they often require surgical intervention for deformity or fracture.

Question 7008

Topic: 10. Pathology and Oncology
A 35-year-old woman presents with chronic, aching pain and progressive stiffness in her left lower extremity. Radiographs reveal dense, irregular, eccentric hyperostosis along the cortex of the left femur and tibia, resembling 'dripping candle wax'. Which of the following clinical features or associations is most characteristic of this disorder?
. High risk of malignant transformation to osteosarcoma.
. Association with precocious puberty and café-au-lait spots.
. Joint contractures and overlying sclerodermatous skin changes.
. Autosomal recessive inheritance pattern.
. Symmetrical bilateral involvement of the long bones.

Correct Answer & Explanation

. Joint contractures and overlying sclerodermatous skin changes.

Explanation

The radiographic description of 'dripping candle wax' (flowing hyperostosis) is pathognomonic for Melorheostosis. This is a rare, non-hereditary sclerosing bone dysplasia linked to somatic mutations in the LEMD3 (MAN1) gene or MAP2K1 gene. It typically affects a single limb (monomelic) and is not symmetrical. Clinically, it is strongly associated with pain, joint contractures, and soft tissue abnormalities, including sclerodermatous skin changes, fibrosis, and vascular anomalies overlying the affected bone. Malignant transformation is exceedingly rare. Precocious puberty is associated with McCune-Albright syndrome.

Question 7009

Topic: Soft Tissue Tumors & Metastasis
A 22-year-old male undergoes a pelvic radiograph following a minor sports injury. The radiograph incidentally reveals numerous small, well-defined, symmetric sclerotic foci clustered around the periarticular regions of the pelvis and proximal femurs. He is completely asymptomatic. If this patient were to exhibit associated cutaneous manifestations, what would be the most likely finding?
. Café-au-lait spots with smooth 'coast of California' borders.
. Dermatofibrosis lenticularis disseminata (connective tissue nevi).
. Subcutaneous hemangiomas with phleboliths.
. Plexiform neurofibromas.
. Sclerodermatous skin thickening over the affected bones.

Correct Answer & Explanation

. Dermatofibrosis lenticularis disseminata (connective tissue nevi).

Explanation

The incidental radiographic finding of multiple small, symmetric sclerotic foci in periarticular regions is characteristic of Osteopoikilosis ('spotted bone disease'). It is an autosomal dominant condition often caused by mutations in the LEMD3 gene. When osteopoikilosis is associated with cutaneous lesions, specifically connective tissue nevi (dermatofibrosis lenticularis disseminata), the condition is known as Buschke-Ollendorff syndrome. Café-au-lait spots with smooth borders are seen in Neurofibromatosis type 1. Hemangiomas are seen in Maffucci syndrome. Sclerodermatous changes are seen in Melorheostosis.

Question 7010

Topic: Bone Tumors

A 10-year-old boy with polyostotic fibrous dysplasia presents with a progressive 'shepherd's crook' deformity of the proximal femur and an impending fracture. Which of the following is the most appropriate surgical management strategy for this deformity?

. Curettage and packing with autologous cancellous bone graft.
. Curettage and packing with allograft cancellous bone.
. Valgus producing osteotomy stabilized with a fixed-angle plate and screws.
. Valgus producing osteotomy stabilized with an intramedullary device.
. Observation and bracing until skeletal maturity.

Correct Answer & Explanation

. Valgus producing osteotomy stabilized with an intramedullary device.

Explanation

Correct Answer: Valgus producing osteotomy stabilized with an intramedullary device.Surgical management of the 'shepherd's crook' deformity in fibrous dysplasia is challenging due to the poor quality of the dysplastic bone. The standard of care involves a valgus-producing osteotomy to correct the mechanical axis, stabilized with an intramedullary device (such as a cephalomedullary nail). Intramedullary fixation is preferred over plates and screws because the entire bone is often diseased; plates create stress risers and have a high failure rate in dysplastic bone. Bone grafting (autograft or allograft) is generally contraindicated as a standalone procedure because the graft is rapidly resorbed and replaced by the host's dysplastic fibrous tissue.

Question 7011

Topic: 10. Pathology and Oncology

A 45-year-old female with a known history of polyostotic fibrous dysplasia presents with a painless, slow-growing soft tissue mass in her right thigh. Magnetic resonance imaging (MRI) reveals a well-circumscribed, intramuscular lesion that is hypointense on T1-weighted images and hyperintense on T2-weighted images. What is the most likely diagnosis of the soft tissue mass?

. Intramuscular lipoma
. Soft tissue hemangioma
. Intramuscular myxoma
. Plexiform neurofibroma
. Undifferentiated pleomorphic sarcoma

Correct Answer & Explanation

. Intramuscular myxoma

Explanation

Correct Answer: Intramuscular myxomaThe association of polyostotic fibrous dysplasia with intramuscular myxomas is known as Mazabraud syndrome. Intramuscular myxomas are benign soft tissue tumors that present as painless, slow-growing masses. On MRI, they are characteristically cystic in appearance, being hypointense on T1 and markedly hyperintense on T2 due to their high mucin content. Recognizing this syndrome is important to avoid misdiagnosing the soft tissue mass as a malignant sarcoma, which could lead to unnecessary radical surgery.

Question 7012

Topic: Bone Tumors

In patients with Multiple Hereditary Exostoses (MHE), forearm deformities are common due to the differential growth of the radius and ulna. Which of the following best describes the typical pathoanatomy of the forearm in these patients?

. Relative overgrowth of the ulna with radial head subluxation
. Shortening of the ulna with secondary bowing of the radius and ulnar deviation of the carpus
. Shortening of the radius with secondary bowing of the ulna and radial deviation of the carpus
. Symmetrical shortening of both radius and ulna with a neutral carpus

Correct Answer & Explanation

. Shortening of the ulna with secondary bowing of the radius and ulnar deviation of the carpus

Explanation

Correct Answer: Shortening of the ulna with secondary bowing of the radius and ulnar deviation of the carpusIn Multiple Hereditary Exostoses (MHE), osteochondromas frequently involve the distal forearm. The distal ulna has a smaller cross-sectional area and contributes a larger percentage to the overall longitudinal growth of the bone compared to the radius. Consequently, osteochondroma formation disproportionately retards ulnar growth. This leads to relative shortening of the ulna, secondary bowing of the radius (which continues to grow but is tethered), ulnar deviation of the carpus, and potential radial head subluxation or dislocation (Madelung-like deformity).

Question 7013

Topic: 10. Pathology and Oncology

A 22-year-old female presents with multiple asymmetric cartilaginous lesions in the metaphyseal regions of her long bones and hands. Physical examination reveals multiple bluish, compressible subcutaneous nodules on her extremities. Which of the following is the most accurate statement regarding her condition?

. The condition is inherited in an autosomal dominant pattern.
. The subcutaneous nodules are neurofibromas.
. She has a significantly higher risk of malignant transformation to chondrosarcoma and visceral malignancies compared to Ollier disease.
. The underlying genetic defect involves the EXT1 or EXT2 genes.

Correct Answer & Explanation

. She has a significantly higher risk of malignant transformation to chondrosarcoma and visceral malignancies compared to Ollier disease.

Explanation

Correct Answer: She has a significantly higher risk of malignant transformation to chondrosarcoma and visceral malignancies compared to Ollier disease.The patient's presentation of multiple enchondromas combined with soft tissue hemangiomas (bluish, compressible nodules) is diagnostic of Maffucci syndrome. Both Ollier disease and Maffucci syndrome are non-hereditary (somatic mutations, typically IDH1/IDH2). However, Maffucci syndrome carries a much higher risk of malignant transformation. The risk of chondrosarcoma is high, and patients also have a significantly elevated risk of developing other visceral malignancies (e.g., ovarian, gastrointestinal, brain tumors), approaching a 100% lifetime risk of some form of malignancy.

Question 7014

Topic: Bone Tumors

A 14-year-old male with polyostotic fibrous dysplasia presents with a progressive 'shepherd's crook' deformity of the proximal femur and a recent impending pathologic fracture. What is the most appropriate surgical strategy for managing this deformity?

. Curettage, autologous bone grafting, and dynamic hip screw fixation
. Valgus-producing proximal femoral osteotomy stabilized with a custom plate and screws
. Valgus-producing proximal femoral osteotomy stabilized with an intramedullary nail
. Resection of the dysplastic bone and reconstruction with a proximal femoral replacement

Correct Answer & Explanation

. Valgus-producing proximal femoral osteotomy stabilized with an intramedullary nail

Explanation

Correct Answer: Valgus-producing proximal femoral osteotomy stabilized with an intramedullary nailThe 'shepherd's crook' deformity is a classic manifestation of fibrous dysplasia in the proximal femur, leading to severe varus and mechanical insufficiency. Surgical correction requires a valgus-producing osteotomy. Because the dysplastic bone is structurally weak and prone to continued remodeling, plate and screw constructs have a high failure rate due to screw pullout. Intramedullary nailing is the biomechanically superior and preferred method of fixation, as it load-shares and protects the entire length of the bone. Autologous bone graft is contraindicated as it will be rapidly resorbed and replaced by dysplastic bone; cortical allograft is preferred if grafting is necessary.

Question 7015

Topic: 10. Pathology and Oncology

A 35-year-old patient presents with chronic, deep, aching pain in the lower extremity and decreased range of motion in the knee. Radiographs reveal irregular, dense, eccentric hyperostosis along the cortex of the femur and tibia, resembling 'dripping candle wax'. Which of the following is most commonly associated with this condition?

. Somatic mutation in the LEMD3 gene
. High risk of malignant transformation to osteosarcoma
. Autosomal recessive inheritance pattern
. Systemic hypocalcemia and hyperphosphatemia

Correct Answer & Explanation

. Somatic mutation in the LEMD3 gene

Explanation

Correct Answer: Somatic mutation in the LEMD3 geneThe clinical and radiographic description ('dripping candle wax' hyperostosis) is pathognomonic for Melorheostosis. This is a rare, non-hereditary sclerosing bone dysplasia. Recent genetic studies have linked melorheostosis to somatic mutations in the LEMD3 gene (also known as MAN1) or the MAP2K1 gene. It is not associated with systemic metabolic abnormalities, is not inherited (it occurs sporadically), and does not have a high risk of malignant transformation.

Question 7016

Topic: 10. Pathology and Oncology

A 28-year-old male with a known history of Multiple Hereditary Exostoses (MHE) presents with a newly enlarging, painful mass over his proximal humerus. Which of the following MRI findings is most highly suspicious for secondary malignant transformation to chondrosarcoma?

. A cartilage cap thickness of 1.0 cm
. A cartilage cap thickness greater than 2.0 cm
. Continuity of the medullary cavity of the lesion with the host bone
. Presence of a well-defined bursa overlying the osteochondroma

Correct Answer & Explanation

. A cartilage cap thickness greater than 2.0 cm

Explanation

Correct Answer: A cartilage cap thickness greater than 2.0 cmMalignant transformation of an osteochondroma to a secondary chondrosarcoma occurs in about 1-5% of patients with MHE. Clinical signs include new onset of pain or growth of the lesion after skeletal maturity. On MRI, the most reliable indicator of malignant transformation is the thickness of the cartilage cap. In an adult, a cartilage cap thicker than 1.5 to 2.0 cm is highly suspicious for chondrosarcoma. Continuity of the medullary cavity is a diagnostic feature of a benign osteochondroma, and an overlying bursa (exostosis bursa) is a common benign finding that can cause pain but does not indicate malignancy.

Question 7017

Topic: 10. Pathology and Oncology

An incidental radiographic finding in a 40-year-old female shows multiple, parallel, linear bands of sclerosis in the metaphyses and diaphyses of the long bones. The patient is completely asymptomatic. This radiographic appearance is the hallmark of which of the following skeletal dysplasias?

. Osteopoikilosis
. Osteopathia striata
. Melorheostosis
. Osteopetrosis

Correct Answer & Explanation

. Osteopathia striata

Explanation

Correct Answer: Osteopathia striataOsteopathia striata (Voorhoeve disease) is a benign, asymptomatic sclerosing bone dysplasia characterized radiographically by multiple, parallel, linear longitudinal bands of sclerosis in the metaphyses and diaphyses of long bones, and sometimes a sunburst appearance in the ilium. Osteopoikilosis presents as multiple small, round sclerotic bone islands. Melorheostosis presents as cortical hyperostosis resembling dripping candle wax. Osteopetrosis presents with generalized, diffuse bone sclerosis ('bone within a bone' appearance).

Question 7018

Topic: Bone Tumors

In the medical management of symptomatic polyostotic fibrous dysplasia, intravenous bisphosphonates are frequently utilized. What is the primary established clinical benefit of this pharmacological therapy in these patients?

. Complete radiographic resolution of the ground-glass lesions
. Prevention of the initial development of McCune-Albright syndrome
. Reduction of bone pain and decrease in bone turnover markers
. Restoration of normal lamellar bone architecture within the dysplastic lesions

Correct Answer & Explanation

. Reduction of bone pain and decrease in bone turnover markers

Explanation

Correct Answer: Reduction of bone pain and decrease in bone turnover markersIntravenous bisphosphonates (such as pamidronate or zoledronic acid) are the mainstay of medical treatment for symptomatic fibrous dysplasia. Their primary proven benefits are the significant reduction of bone pain and the normalization of biochemical markers of bone turnover (e.g., alkaline phosphatase). However, bisphosphonates do not cure the disease; they do not lead to radiographic resolution of the lesions, nor do they restore normal lamellar bone architecture or prevent the endocrine manifestations of McCune-Albright syndrome.

Question 7019

Topic: Bone Tumors

A 4-year-old boy presents with a painless, hard, asymmetrical swelling on the medial aspect of his right knee, causing a valgus deformity. Radiographs show an irregular, ossified mass arising off the medial epiphysis of the distal femur. What is the most likely diagnosis?

. Multiple hereditary exostoses
. Ollier disease
. Dysplasia epiphysealis hemimelica
. McCune-Albright syndrome
. Maffucci syndrome

Correct Answer & Explanation

. Dysplasia epiphysealis hemimelica

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is characterized by an asymmetric osteochondroma-like overgrowth arising directly from the epiphysis, most commonly affecting the medial side of the knee or ankle in young boys.

Question 7020

Topic: 10. Pathology and Oncology

A 3-year-old child presents with painful, soft tissue swellings over her upper back following a minor fall. Physical examination reveals bilateral short great toes with valgus deviation. A biopsy of the back mass is being considered. Which gene is mutated in this condition, and what is the recommendation regarding the biopsy?

. GNAS; biopsy is essential to rule out sarcoma
. EXT1; biopsy is contraindicated due to bleeding risk
. COMP; biopsy is recommended for definitive diagnosis
. ACVR1; biopsy is absolutely contraindicated
. SOX9; biopsy is recommended but delayed until skeletal maturity

Correct Answer & Explanation

. ACVR1; biopsy is absolutely contraindicated

Explanation

Fibrodysplasia Ossificans Progressiva (FOP) is caused by an ACVR1 gene mutation. It classically presents with congenital malformation of the great toes and episodic heterotopic ossification. Biopsy or any surgical trauma is strictly contraindicated as it will trigger explosive heterotopic bone formation.

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