Temporal Bone Systemic diseases

Question 1

What are the different types of dysplasia’s that affect the temporal bone?

Answer 1

1. Fibrous dysplasia
2. McCune-Albright Syndrome
3. Hyperparathyroidism
4. Paget’s disease
5. Osteogenesis Imperfecta (Van Der Hoeve Syndrome)
6. Osteopetrosis (Albers-Schoenberg)

Question 2

Discuss the types of osteogenesis imperfecta. What are the common features to all types?

What is the etiology of osteogenesis imperfecta? What is the etiology of the conductive hearing loss?

Answer 2

Common features:
1. Short stature
2. Scoliosis
3. Frequent fractures/bone deformities
4. Easy bruising

TYPES OF OSTEOGENESIS IMPERFECTA:

1. TYPE I: Van Der Hoeve-de-Kleyn syndrome
   - Inheritance: Autosomal Dominant
   - Mildest form
   - Features: Nondeforming pediatric fractures, normal stature, blue sclerae, CHL
2. TYPE II
   - Inheritance: Autosomal Recessive
   - Most severe type, lethal in utero or shortly after
   - Features: Shortened long bones, beaded ribs, platyspondylisis, calvarial demineralization
3. TYPE III
   - Inheritance: Variable inheritance
   - Features: Progressive growth failure, frequent fractures, severe deformity, dentinogenesis imperfecta, grey sclerae, CHL or SNHL
4. TYPE IV
   - Inheritance: Autosomal Dominant
   - Intermediate severity between Types I and III
   - Features: White sclerae

Order of severity: Type I, IV, III, II

ETIOLOGY:
- Mutations in COL1A1 (Chromosome 17q21) & COL1A2 genes (Chromosome 7q21) - encodes collagen
- Type 1: CHL associated with blue sclerae; SNHL associated with Grey Sclerae

Conductive hearing loss: Occurs from structural changes in the ossicles, microfractures of the manubrium; fragility of the long process of the incus and fracture or resorption of the crura of the stapes

Question 3

What are the four features common to all osteogenesis imperfecta patients?

Answer 3

1. Short stature
2. Triangular-shaped face
3. Breathing problems
4. Hearing loss
5. Brittle teeth
6. Bone deformities (bowed legs or scoliosis)

Question 4

What are the middle ear anomalies of osteogenesis imperfecta that make stapes surgery more difficult?

Answer 4

1. Microfractures of the ossicles
2. Incus fracture/erosion
3. Stapedectomy can give results similar to those seen with otosclerosis, but is extremely delicate - crimping the prosthesis around the incus may cause a pathologic fracture

Question 5

Discuss fibrous dysplasia of the temporal bone:
1. What is fibrous dysplasia?
2. Epidemiology?
3. Histology
4. Types
5. Features (especially for temporal bone)
6. Imaging
7. Treatment

Answer 5

Fibrous dysplasia = replacement of normal medullary bone with fibro-osseous tissue

EPIDEMIOLOGY:
- Presents before age 30
- 25% occurs in H/N (mainly maxilla)

HISTOLOGY:
- Metaplastic bone in the form of irregular, feathery, “chinese letter” pattern
- Diffuse blending of margins
- Fibrous connective tissue stroma arranged in a whorled pattern
- Occasional osteoblastic rimming (vs. in ossifying fibroma - always osteoblastic rimming with clear borders)

TYPES:
1. Monoostotic (80%)
2. Polyostotic (17%)
3. McCune-Albright syndrome (3%)
- GNAS1 gene (20q13) - ≥2 or 3 polyostotic disease associated with triad of hyperpigmentation, precocious puberty and endocrinopathy (thyroid/parathyroid)

Features (especially temporal bone):
- Lesions typically present as painless enlarging bony swelling
- Can get progressive narrowing of EAC with CHL - most common manifestation, and occurs in 80% and can be mistaken for exostoses
- Can have facial palsy and dysequilibrium
- In HN maxilla is most commonly involved

INVESTIGATIONS:
1. Labs: no elevation in ALP (main sources of ALP are liver and bones; however fibrous dysplasia there is NO elevation of ALP)
2. Imaging: CT - eggshell cortex, sclerosis and ground glass appearance

TREATMENT:
1. Surgical recontouring ± facial nerve decompression
2. Can try bisphosphonate if bone pain

Question 6

Discuss Paget’s disease in the context of the temporal bone:
1. Triad of features
2. Pathophysiology
3. Clinical presentation (esp temporal bone)
4. Diagnosis
5. Treatment

Answer 6

Triad of features:
1. Enlarging skull
2. Dorsal kyphosis
3. Bowing legs

PATHOPHYSIOLOGY:
- Localized disorder of bone remodelling, excessive bone resorption followed by increase in bone formation
- Leads to structurally disorganized mosaic of bone that is weaker, larger, less compact, more vascular, and fragile
- Lumbosacral area most common, usually polystotic

CLINICAL PRESENTATION:
1. 70-90% asymptomatic
2. Bone pain / osteoarthritis
3. Temporal bone: CHL or SNHL, vertigo, tinnitus
4. Mostly multifocal
5. Progressive at the affect site
6. In HN, skull is most commonly involved

DIAGNOSIS
1. Most radiological: Sclerosis and lytic lesions or bone
2. Labs: Serum ALP usually elevated (contrast to fibrous dysplasia) - sign of active disease, Normal Ca2+ and PTH
3. Can have elevated urine hydroxyprline

TREATMENT:
1. If symptomatic and elevated ALP (sign of active disease) - treat with nitrogen-containing bisphosphonates, calcitonin (if Calcium elevated), etidronate, and mithramycin (antineoplastic antibody)

Question 7

What are five main differences between fibrous dysplasia and paget’s disease?

Answer 7

1. Age of onset: < 30 for FD, >40 for Paget’s
2. Type: Monoostotic most common for FD, Polyostotic most common for Paget’s
3. Location: FD mostly ribs, femur, maxilla often involved in HN; Paget’s usually lumbar spine, in HN skull often involved
4. Labs: FD not usually ALP elevated, Paget’s usually ALP elevated in active disease
5. Treatment: FD surgical recontouring; Paget’s medical - bisphosphonates, calcitonin for elevated Ca