Page 235 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

The following clinical signs may result: appearance 3 weeks postoperatively, but a gradual
increase in the size of the thoracic cavity and movement
VetBooks.ir • Cardiac insufficiency may result from a mediastinal along with a degree of clinical improvement.
of the diaphragm was recorded over the following year,
• Pulmonary function may be compromised by the
reduction in intrathoracic volume
shift and compression of the vena cava
• Regurgitation may result from the change in gastro- Tumours of the diaphragm
oesophageal angle as the stomach is displaced. Tumours affecting the diaphragm are rare. There are
case reports of the diaphragm being affected by primary
Acquired eventration may respond to symptomatic tumours (e.g. peripheral nerve sheath tumour), disseminated
therapy and may be transient in nature. Congenital even- tumours (e.g. mast cell leukaemia and meso thel ioma)
tration has been managed by plication of the atrophic and metastases (e.g. bronchogenic adenocarcinoma and
areas of the diaphragm (Merdan Dhein et al., 1980). haemangiosarcoma). Although rare, mass lesions affecting
the diaphragm must be differentiated from mass lesions of
Diaphragmatic paralysis the caudal lung lobes and caudal mediastinal structures,
rupture of the diaphragm and pleuroperitoneal hernia.
Diaphragmatic paralysis is the most important functional Management of these lesions presents a consider able chal-
disorder of the diaphragm but is rarely reported (Young et lenge in terms of performing a biopsy, surgical excision and
al., 1980; Suter, 1984; Greene et al., 1988; Vignoli et al.,
reconstruction of the resulting deficit.
2002). It may be caused by a lesion in the cervical spinal
cord, phrenic nerves, neuromuscular junction or diaphrag-
matic musculature. A number of aetiologies have been Synchronous diaphragmatic contraction
suggested. These include: a primary diaphragmatic myo- This condition is rare and only a few cases have been
pathy; toxoplasmosis; bilateral phrenic neuritis; organo- described (Detweiler, 1955; Smith, 1965; Bohn and
phosphate toxicity; external trauma; and iatrogenic trauma Patterson, 1970; Mainwaring, 1988), but it may be more
during thoracic surgery. frequent than the paucity of case reports suggests.
Paralysis may be unilateral or bilateral and temporary A number of causes have been suggested and these
or permanent. Diaphragmatic paralysis might be expected include: trauma to the thorax; prolonged vomiting; gastric
to have a major effect on ventilation. However, given irritation; electrolyte imbalance with alkalosis; uraemia;
that chest wall expansion is also provided by contraction
encephalitis; and post-surgical. Of these, chronic vomiting
of the internal intercostal muscles, some respiratory and thoracic trauma account for the majority of cases.
movements may be made. Experimental division of both In this condition, each time the heart beats, one or
phrenic nerves is claimed not to affect ventilation both phrenic nerves are stimulated and the diaphragm
adversely or to cause respiratory insufficiency (De Troyer contracts (Suter, 1984). It is hypothesized that if the
and Kelly, 1982). However, diaphragmatic paralysis threshold of excitability of the phrenic nerves is
caused by naturally occurring disease is a cause of respir- decreased, their pericardial portion may be stimulated by
atory insufficiency (Young et al., 1980; Greene et al., 1988;
the cardiac action potentials. This reduction in the thresh-
Vignoli et al., 2002). old of excitability may be caused by alkalosis, hypo-
The cardinal sign of diaphragmatic paralysis is severe
calcaemia, hypokal aemia and hypochloraemia, which
orthopnoea in the absence of abnormal heart or lung explains the association with chronic vomiting. However,
sounds. Paradoxical inward movement of the abdominal
serum electrolyte and blood gas analysis has not been
muscles on inspiration may be seen, particularly in dorsal
recumbency. Unilateral paralysis may be asymptomatic. performed in any case thought to be due to these
mechanisms.
Other clinical signs, representing the underlying disease
process, may also be noted. In addition, thoracic trauma may alter the anatomical
Thoracic radiography reveals a small thoracic cavity relationships between the phrenic nerve and the heart,
resulting in stimulation of the phrenic nerves by cardiac
with cranial displacement of the diaphragm. However, the
radiographic appearance of the diaphragm is variable action potentials (Mainwaring, 1988). The left phrenic
nerve crosses both ventricles as it passes caudally in the
depending on patient size, X-ray beam centring, phase of
respiration, gravity, age and breed, and a dynamic study thorax, whereas the right phrenic nerve crosses the right
atrium but not the ventricles. It is hypothesized that the
may be required to reach a definitive diagnosis. On fluor-
oscopy, contraction of the diaphragm is absent and para- closer proximity of the left phrenic nerve to the ventricles
doxical cranial displacement of the flaccid diaphragm predisposes to left-sided diaphragmatic contraction. In
may be seen (Greene et al., 1988). These imaging tech- all cases where this information has been recorded, con-
niques will differentiate unilateral from bilateral paralysis. traction of the left side only or both sides, with the left
Ultrasonography is as sensitive as fluoroscopy, but is side being more forceful, has been noted.
less hazardous and more easily performed, and may rule A visible or palpable ‘pulse’ may be detected over the
out other lesions of the diaphragm (Vignoli et al., 2002). thoracic wall on one or both sides. Simultaneous ausculta-
Percutaneous stimulation of the phrenic nerves may iden- tion of the heart confirms its association with systole.
tify denervation of the diaphragm (Greene et al., 1988). Subclinical cases may be detected by echocardiography.
Post-traumatic diaphragmatic paralysis may be a This condition is generally self-limiting and no treat-
transient phenomenon, requiring only symptomatic and ment is necessary. Some cases have been treated
supportive therapy of the respiratory system. Plication of with intravenous fluids or intravenous phenobarbital, with
the central tendon of the diaphragm with interlocking apparent success (Mainwaring, 1988). In some cases,
interrupted inverting polypropylene sutures has been however, the condition may persist for months (Bohn
attempted, which resulted in a taut, non-mobile dia- and Patterson, 1970). The prognosis is determined
phragm intraoperatively (Greene et al., 1988). This had primarily by the nature and severity of the underlying
minimal effect on the radiographic or fluoroscopic disease process.

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