Thick Skull, Generalized

Miral D. Jhaveri, MD

DIFFERENTIAL DIAGNOSIS

Common

Skull Normal Variants
- Diffusely Thick Skull, Normal
- Hyperostosis Frontalis Interna
Phenytoin (Dilantin) Use, Chronic
Shunted Hydrocephalus
Metastases (Diffuse Sclerotic)
Paget Disease

Less Common

Microcephaly
Fibrous Dysplasia
Hyperparathyroidism
Acromegaly
Subdural Hematoma, Chronic (Calcified)
Anemias
- Iron Deficiency Anemia
- Sickle Cell Disease
- Thalassemia
Extramedullary Hematopoiesis

Rare but Important

Sclerosing Bone Dysplasias
- Osteopetrosis
- Pycnodysostosis
- Melorheostosis
Fluorosis

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Diffuse diploic space expansion with/without adjacent cortical thickening
Most common cause by far of “thick skull” = normal variant!

Helpful Clues for Common Diagnoses

Skull Normal Variants
- Most common cause
- Females normally have significantly thicker parietal/occipital bones than males
- Hyperostosis frontalis interna
  - Usually bilateral, symmetrical
  - Spares areas occupied by superior sagittal sinus, cortical venous channels
  - Often ends at coronal sutures
  - May extend to parietal bones, orbital roofs
  - Females > 35 years old
  - No clinical significance
  - Etiology unknown
Phenytoin (Dilantin) Use, Chronic
- Look for combination of thick skull + cerebellar atrophy = probable chronic Dilantin therapy
- Up to 34% among patients with seizure disorder + anticonvulsant therapy
Shunted Hydrocephalus
- Chronic shunted hydrocephalus often associated with diffuse calvarial thickening
- Look for thick skull + shunt + chronic collapsed ventricles
Metastases (Diffuse Sclerotic)
- Fat-suppressed T1 C+ scans helpful in detecting calvarial, subtle dural metastases
- Common with prostate & breast metastasis
- Look for associated focal/diffuse dura-arachnoid involvement
Paget Disease
- Initial osteolytic change of skull in osteoporosis circumscripta
- Late osteosclerotic phase
  - Osteoblastic areas crossing sutures
  - Marked thickening of the diploic space
  - “Tam-o’-shanter” skull
  - Focal areas of sclerosis in expanded diploic space: “Cotton wool” appearance (of skull)
- Platybasia with basilar invagination

Helpful Clues for Less Common Diagnoses

Microcephaly
- Skull overgrowth occurs secondary to small brain
- Small brain causes = developmental anomalies or a result of very early insult
Fibrous Dysplasia
- Can involve any aspect of skull
- Can be focal or extensive
- Medullary expansion with ground-glass appearance is classic
- Four disease patterns
  - Monostotic (70-80%)
  - Polyostotic (20-30%)
  - Craniofacial (can be isolated; up to 50% of polyostotic)
  - Cherubism (mandible, maxilla)
Hyperparathyroidism
- Granular appearance of skull with multiple areas of normal bone interspaced between
  - “Salt & pepper” or “pepper pot skull” appearance
- Loss of distinction of inner & outer table
- Loss of lamina dura
- Brown tumors
- Chronic renal disease: Secondary hyperparathyroidism
- ↑ Serum calcium, ↑ parathyroid hormone, ↓ serum phosphorus
Acromegaly
- Calvarial hyperostosis (esp. inner table)
- Prognathism (elongation of mandible)
- Sellar enlargement, erosion
- Enlarged paranasal sinuses (mainly frontal): 75%
- ↑ Growth hormone & IGF-1
Subdural Hematoma, Chronic (Calcified)
- Chronic calcified subdural hematoma along inner table simulates thick skull
- Look for subtle cleavage between calcified membranes and the inner table
  
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