疾病介紹-水腦症
(Hydrocephauls)
水腦症，原發性的水腦症是因為蜘蛛膜小樑對腦脊液的再吸收出現異常。其他的原發性水腦症也有可能因為中腦導水管的阻滯導致腦脊液流動受阻。也有特例是蒙羅氏小孔阻塞引起的。雖然原發性的水腦症在某特殊的品種中為遺傳性的(例：約克夏)。在某些玩賞犬，其發生率確相當的高 (如：吉娃娃、約克夏、曼徹斯特梗、博美犬、小型貴賓) ，還有些頭形圓形的種類(
如：英國牛頭梗、波士頓梗、北京犬及拉薩犬) 水腦症的臨床症狀常見有：癲癇、視力不良、學習能力遲緩及痴呆。在某些( 並非全部)
先天性水腦症的病例中，會發現囟門沒有閉鎖。當然，囟門閉鎖不全的現象並不能當作診斷的依據，因為很多相同現象的動物並沒有水腦症的現象。很多原發性水腦症的病例有圓且突出的頭蓋骨。有些病例會有雙眼斜視，原發性的水腦症，其臨床症狀的變化緩慢，且有些病畜其臨床症狀會漸漸穩定。也有少部分的病例其病程會突然惡化。在解剖時常會發現腦室內有出血及腦膜破裂的現象，此種病理現象至今仍不明。
次發性的水腦症起因在於腦脊髓液的流動性受損。可能的原因也許是因為腦室的阻滯( 例如腦瘤
)，或是腦蜘蛛膜絨毛缺損造成腦脊液再吸收不良。造成吸收不良的原因可能是腦室感染引起。水腦引起的病因也可能造成中腦導水管的狹窄，當動物因為水腦症死亡而進行屍體解剖時，常常無法發現這個現象(中腦導水管狹窄
)。病畜常有中樞神經感染或頭部創傷性的傷害之病史。維他命A不足也會造成蜘蛛膜對腦脊液出現吸收障礙。次發性的水腦症通常會成顱內壓持續性及全面性的上升。所以也很難評斷顱內壓的上升是因為原來的病程或是水腦症所引起的。在原發性的水腦症中，x光檢驗下，腦殼也許會變的比較薄，且腦迴的圖樣會消失。對照腦室的影像可以很準確的診斷水腦症，但是很少以此當作最後診斷的依據，因為有更好的診斷工具。假設病畜的囟門沒有閉合，可以用超音波直接診斷，會發現腦室空腔變大，這種檢驗方式對原發性的水腦症相當有用。更先進的檢驗儀器，如核磁共振(Magnetic Resonance Imaging; MRI)或斷層掃描(Computerized Tomography; CT) 可以確切診斷原發性或次發性之水腦症，甚至可找出次發性水腦症的潛在因素。腦脊液的收集可以測量壓力的增加。水腦症的治療，應要先評估其為原發性或次發性。如果是次發性，則應在潛在病因發現前先降低顱內壓。為了干擾壓力的增加，應該嘗試減少腦脊液的生成或增加再吸收藥物學上使用類固醇可以增加腦脊液的吸收，有些報告甚至顯示該藥物也可以減少腦脊液的生成。所以，類固醇可適用在原發性或次發性的水腦症。原發性的水腦症，長期使用類固醇(Prednisolone) 的效果有限。有些利尿劑，如Furosemide,
也可以抑制腦脊液的生成。短期的利尿劑，可以降低顱內壓，但是長期使用可能會造成體內離子的不平衡。在某些病例中，手術引流有不錯的效果。在很年輕的病歷，手術的併發症可能會比較高。對原發性的病畜來說，早期發現再加上適當的治療通常有不錯的效果，但是痊癒後，動物本身的學習能力會變差。而次發性的水腦症，其癒後的效果就不甚良好。
Primary (congenital) hydrocephalus is apparently
due to failure of arachnoid villi to resorb CSF at an adequate rate. Other cases
of congenital hydrocephalus involve a narrowed mesencephalic aqueduct with
obstruction to CSF flow. Unilateral
cases may involve obstruction of the foramen of Monro. Although primary
hydrocephalus appears to be hereditary in some breeds (e.g., Yorkshire
terriers), it is a spontaneous malformation in others. The highest incidence is
in toy breeds (Chihuahua, Yorkshire terrier, Manchester terrier, Pomeranian, toy
poodle) and in brachycephalic breeds (English bulldog, Boston terrier,
Pekingese, Lhasa apso). The most common clinic findings in patients with
hydrocephalus include: seizure, visual deficits, slowed learning, and dementia.
Some, but not all, congenital hydrocephalics have an open fontanelle. The
presence of an open fontanelle should never be considered as diagnostic of
hydrocephalus because it may occur as a normal variant in otherwise healthy
dogs. Many congenital hydrocephalics have a dome-shaped, prominent calvarium.
Some affected patients have a bilateral divergent strabismus, referred to as a
setting “sun sing.” Although the clinic course in congenital hydrocephalus
is usually slowly progressive, the condition appears to stabilize in some
patients. A small number of patients with hydrocephalus have sudden,
catastrophic worsening of their condition. At necropsy, these patients are
commonly found to have intraventricular hemorrhage and internal capsular tears.
The pathogenesis of these secondary changes remains unknown.
Secondary (noncomunicating) hydrocephalus results from impaired movement
of CSF. This may be due to ventricular obstruction (e.g., secondary to neoplasms)
or to impaired CSF resorption at the arachnoid villi, usually as a consequence
of prior inflammation. Infectious causes of hydrocephalus may also result in
narrowing of the mesencephalic aqueduct; inflammatory changes may no longer be
present at the time of postmortem examination. Affected animals often have a
history of recent inflammatory CNS disease or traumatic head injury.
Hypovitaminosis A causes hydrocephalus by altering CSF resorption at the
arachnoid granulations. Secondary hydrocephalus is often rapidly progressive and
is associated with massive elevations of ICP. It is difficult in these patients
to distinguish between the signs resulting from the primary pathologic process
and those from the hydrocephalus.
In
primary hydrocephalus, skull radiographs may demonstrate a thin calvarium. These
same patients will lose the radiographic, bony gyral pattern. Contrast
ventriculography will definitively diagnose this condition, but is rarely
performed owing to improved diagnostic imaging techniques. If an affected
patient has an open fontanelle, ultrasonography of the ventricles may be to
demonstrate the ventricular enlargement. This is most usefull in primary
hydrocephalus. Enhanced imaging techniques, such as MRI or CT scanning, confirm
the presence of hydrocephalus (whether primary or secondary) and may reveal the
underlying causes in secondary hydrocephalus. CSF collection has been used to
measure pressure increases. Increased pressure is an inconsistent finding in
primary hydrocephalus, and collecting CSF in patients with secondary
hydrocephalus may be dangerous as the elevations in pressure may result in brain
herniation.
Therapy
of hydrocephalus depends on whether the patient has primary or secondary
hydrocephalus. If secondary, the ICP must be decreased before the underlying
etiology is treated. To effect this decrease, one should try to decrease CSF
production or increase CSF resorption., Medical treatment with steroids is known
to increase CSF resorption, and some reports indicate that they also diminish
the rate of production of CSF. Thus, steroids may be used in either primary or
secondary hydrocephalus. There has been limited success in the long-term therapy
of primary hydrocephalus with maintenance prednisolone. Diuretics, such as
furosemide, diminish CSF production. Short-term administration of diuretics may
decrease ICP, but their long-term use may be associated with systemic
electrolyte disturbances.
Surgical drainage has been of benefit in some cases. This
requires permanent placement of a ventriculovenous (or ventriculoperitoneal)
shunt. Surgical is described elsewhere. In very young patients, the surgical
complication rate can be high.
For
primary hydrocephalus, the prognosis appears to be fair if the condition is
diagnosed early and treated appropriately. Affected animals may always be dull
and have limited ability to learn, but may make acceptable pets. The prognosis
is generally worse in patients with secondary hydrocephalus.
參考資料
References
１．
Stephen J. Ettinger, Edward C. Feldman. Textbook of veterinary
internal medicine. Saunders, 1995. p 616-627.
２．
Michael D. Lorenz, Larry M. Cornelius. Small Animal Medical
Diagnosis. Lippincott, 1993. p 449-456.
３．
Ronald L. Burk, Norman
Ackerman. Small Animal Radiography and Ultrasonography. Saunders. P 559-562.
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