Craniosynostosis

From Cat
Suspect craniosynostosis in a 6-week-old Persian, with anterior deviation of the cranium. Photo courtesy Dr Jim Euclid
Radiograph of above cat, showing dorsal ridging of the squama frontalis bones. Courtesy Dr Jim Euclid
CT scan of above kitten showing prominent dorsal ridging of anterior cranium. Courtesy Dr Jim Euclid

Feline craniosynostosis is a rare congenital disease characterized by early closure of cranial suture lines, leading to cranial skeletal malformations[1].

In cats, a breed predisposition has been reported in the Persian[2] and this developmental anomaly appears to be a genetic disease unrelated to bony defects observed with nutritional secondary hyperparathyroidism.

In humans, this disease is an autosomal-recessive hereditary condition[3] caused by premature fusion of temporal growth plates resulting in dorsal or rostral deviations of the skull.

Hereditary human craniosynostoses are caused by mutations in the fibroblast growth factor receptor 1, 2 or 3 (FGFR1, FGFR2, FGFR3) genes as well as a transcription factor gene called transcription factor TWIST. The diagnosis of non-syndromic craniosynostosis is specifically based on the identification of a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene[4]. Human craniosynostosis can also be a congenital disease due to exposure to mutagens in utero (particularly cyclophosphamide[5], nitrosatable drugs[6] or processed meats[7]).

In human craniosynostosis, visual deficits are commonly observed associated with this condition, due primarily to abnormal displacement of the cribriform plate and ethmoid turbinates, resulting in compression of the optic chiasma. In dogs, which have a form of deliberate craniosynostosis, as is seen in brachycephalic dog breeds such as the Pug or Boxer, concurrent visual deficits are not normally evident, despite low olfactory bulb angles and ventral olfactory bulb orientations[8].

Unlike humans where concurrent open fontanelles, chiari malformations, visual impairments and cerebral hypertension are frequently associated with this condition, these symptoms have neither been reported or detected in cats. Despite this, the growth plate-dependent nature of cranial development in cats is similar to most other mammals, and it is likely this condition occurs but has yet to be academically reported.

From anecdotal reports[9], affected cats are usually young at time of diagnosis and may present with either dorsal or rostral deviation of the cranium. Prominent ridging of the head may be palpable and this condition is frequently dismissed as an aberrant but innocuous undiagnosed malformation.

Clinically affected patients typically present with craniodorsal ridging, usually affecting the frontal bones as a symmetrical deformation.

Definitive diagnosis requires skull imaging with radiography, CT or MRI.

A differential diagnosis would include hydrocephalus (which is usually associated with neurological symptoms), brachycephalic syndrome in Persian cats, anemia-induced porotic hyperostosis[10], in utero herpesvirus infection, intracranial meningioma (usually older cats)[11] and cleft palate (mainly newborn kittens)[12].

In the majority of cases, close monitoring for symptoms such as mental developmental disorders or seizures is important.

In deteriorating cases, corrective cranioplasty or euthanasia are the only viable options.

References

  1. Vidal Sanahuja R et al (2012) Presentation of two cases of Crouzon syndrome: allelic cranio-stenotic conditions of FGFR genes. An Pediatr (Barc) 77(4):272-278
  2. Dr Jim Euclid (2013) pers comm
  3. Senarath-Yapa K et al (2012) Craniosynostosis: Molecular pathways and future pharmacologic therapy. Organogenesis Oct 1
  4. Chun K et al (2003) Screening of patients with Craniosynostosis: Molecular Strategy. American Journal of Medical Genetics 120A:470-473
  5. Enns GM et al (1999) Apparent cyclophosphamide (cytoxan) embryopathy: a distinct phenotype? Am J Med Genet 86(3):237-241
  6. Olshan AF & Faustman EM (1989) Nitrosatable drug exposure during pregnancy and adverse pregnancy outcome. Int J Epidemiol 18(4):891-899
  7. Hord NG et al (2009) Food sources of nitrates and nitrites: the physiologic context for potential health benefits. Am J Clin Nutr 90(1):1-10
  8. Hussein AK et al (2012) Effect of brachycephalic, mesaticephalic, and dolichocephalic head conformations on olfactory bulb angle and orientation in dogs as determined by use of in vivo magnetic resonance imaging. Am J Vet Res 73(7):946-951
  9. Euclid, JM (2013) pers comm
  10. Gerszten PC et al (1998) Diseases of the skull in pre-Columbian South American mummies. Neurosurgery 42(5):1145-1151
  11. Karli P et al (2013) Extracranial expansion of a feline meningioma. J Feline Med Surg Jan 7
  12. Oechtering GU et al (2010) Brachycephaly in dog and cat: a "human induced" obstruction of the upper airways. Pneumologie 64(7):450-452