ACRANIA (Absent Cranial Vault)

 

 

Anencephaly

Exencephaly

Iniencephaly

Flat bones of

calvarium

Absent

Partial or Complete  absence

* Partial or complete absence.
* Defect in squamous occipital bone:
Apertus = with encephalocele

Clausus = without encephalocele

 

Skull base

N

N

* Dysraphic defect in occiput.
* Enlarged foramen magnum.

Fetal neck

N

N

* Persistent hyperextension.
* Occiput close to or fused with back.

Cervical
Spine

N

N

* Hyperextended
* Shortened by block vertebrae.
* No laminae or spines.

 

 

 

Cerebral tissue

Absent - occasional remnants of forebrain

Present but:
- abundant
- disorganized
- covered by a thin     membrane.

Normal or absent if associated with anencephaly or abundant and disorganized if associated with exencephaly.

 

 

 

Brainstem

Partially present esp medulla.

Present.

Usually present.

Other signs

* Frogs eye:
* bulging eyes
* large tongue

* short neck
+/- polyhydramnios

 

 

 

 

 

Pathology

Primary non closure of ant. neuropore or secondary degeneration of closed neuropore

? Failure of mesenchymal migration

Unknown

 

 

REFERENCES

  1. Ekici E, Gulmezoglu AM. Sonographic Diagnosis of Fetal Acrania. J Clin Ultrasound 1991, 19:363-366.
  2. Yang YC, Wu CH, Chang FM et.al. Early Prenatal Diagnosis of Acrania by Transvaginal Ultrasound. J Clin Ultrasound 1992,20:343-345.
  3. Kennedy KA, Flick KJ, Thurmond AS. First-trimester diagnosis of exencephaly. Am J Obstet Gynecol 1990, 162:461-463.
  4. Cox GG, Rosenthal SJ, Holsapple JW. Exencephaly: Sonographic Findings and Radiologic-Pathologic Correlation Radiology 1985, 155:755-756.
  5. Mannes EJ, Crelin ES, Hobbins et.al. Sonographic demonstration of Fetal Acrania AJR 1982, 139:181-182.
  6. Shere DM, Hearn-Stebbins B, Harvey W et.al. Endovaginal Sonographic Diagnosis os Iniencephaly Apertus and Craniorachischisis at 13 Weeks, Menstrual Age. J Clin Ultrasound 1993, 21:124-127.