585
investigation and requested that euthanasia be undertaken.
They would not consent to a post mortemexamination.
Histopathology
Several sections taken from the tracheal wall biopsy displayed
similar changes (Figs 4and 5). The respiratory epithelium and
lamina propriawere normal, but at the deep margin of the
lamina propria there were moderately well-demarcated
cartilaginous nodular masses. These nodules consisted of
centripetally-orientated, irregular sheets and nests of large
chondrocyte-like cells. These had a moderate amount of
vacuolated pale cytoplasm and a small chromatin-rich nucleus.
Multifocally, some chondrocytes showed degenerative
change. There was an abrupt transition to an eosinophilic
matrix with lacunae containing osteocytes. These latter cells
surrounded a central homogeneous eosinophilic matrix with
lacunae (osteoid/bone).
The histopathological appearance of the tracheal wall
nodule indicated osseo-cartilagenous nodular proliferation
with ossification. This histological appearance was considered
to be consistent with either tracheobronchopathia
osteochondroplastica, chondrodysplasia or osteochondroma. In
view of the cobblestone appearance with multiple tracheal and
bronchial nodules and their distribution, a tentative diagnosis of
tracheobronchopathia osteochondroplastica was made.
Discussion
Tracheobronchopathia osteochondroplastica is a rare benign
human condition characterised by the presence of bony and
cartilaginous nodules in the tracheal and bronchial mucosa
and submucosa (Meyer et al.1997). The aetiology and
pathogenesis of the disease remain unknown. Although
patients with severe disease may present with signs of
dyspnoea, haemoptysis or pneumonitis, most cases are
asymptomatic and are frequently diagnosed incidentally
during routine bronchoscopic examination or during difficult
intubations or at radiological examinations (Meyer et al.1997;
Karlikaya et al.2000; Leske et al.2001; Hussain and Gilbert
2003; Doshi et al.2005). The acute presentation of this pony
and initial clinical signs of dyspnoea and emphysema were due
to tracheal rupture; the nodular disease of the trachea was a
discovery made during the work up of the case, and it is
unclear whether this disease predisposed to tracheal rupture
or whether it was coincidental. Nodules in
tracheobronchopathia osteochondroplastica are most
frequently present in the trachea and mainstem bronchi (as in
the pony described here), although occasionally they can be
present in the larynx and smaller airways. In man, the
distribution of nodules tends to be confined to the anterior
and lateral walls of the trachea, reflecting the distribution of
cartilage in the tracheal wall. The nodules had a similar
distribution in this pony, which probably reflects the fact that
the cartilage rings are incomplete dorsally. As in the present
case, the nodules in human cases are characteristically firm
(giving rise to a grating sensation when a bronchoscope ispassed); in man, this is considered a useful finding that helps
to distinguish tracheobronchopathia osteochondroplastica
from other nodular tracheal diseases (Leske et al.2001). There
appears to be only one other reported case in a domesticated
animal, a 9-year-old West Highland White Terrier that
presented with intermittent signs of respiratory difficulty,
especially after exercise (Sellon et al.2005). The dog was
subjected to euthanasia almost 4 years after the initial
diagnosis due to severe dyspnoea.
Other conditions of the tracheal cartilage that were
considered in this case included osteochondroma and
chondrodysplasia. Osteochondroma is derived from aberrant
cartilaginous epiphyseal growth plate tissue (Milgram 1983). It
has not been previously reported as a lesion of the equine
trachea although it has been found in the equine distal limb
and the nasal bone (Adair et al.1994). Chondrodysplasia is a
rare congenital condition reported in Texel sheep (Thompson
et al.2005), and is reported as part of syndromes seen in man:
Conradi-Hunerman syndrome (Hochman and Fee 1987), and
Kniest dysplasia (Hicks et al. 2001). Osteochondral dysplasia of
the canine trachea has been reported. Chondrodysplasia of
the equine trachea has not been reported, although
congenital abnormalities of cartilage rings, including tracheal
collapse associated with dorsoventral flattening of the
cartilage rings in Shetlands and Miniature horses, are
recognised (Martin 1981; Mair and Lane 1990, 2005), and
may represent a form of chondrodysplasia. Tracheal collapse
and rupture have been described in association with
chondrodysplasia in both man and the dog (Mawby et al.
2006). The tracheal collapse in this case was caused by extra-
and intraluminal compression resulting from subcutaneous,
peritracheal and intramural emphysema, which was
compounded by intraluminal obstruction due to mucosal
inflammation and the presence of the nodules.
The nodular appearance to the ventral and lateral
surfaces of the trachea is not described as part of any of the
chondrodysplastic conditions seen in other animals. Other
possible differentials for nodular disease in the equine
trachea include parasitism, nodular amyloidosis, eosinophillic
granulomas and tracheal neoplasia. On the basis of the
results of histopathology, these conditions were excluded,
and a tentative diagnosis of tracheobronchopathia
osteochondroplastica was reached. The present case
exhibited similarities to the condition described in man in
that there were no previously reported clinical signs of
respiratory disease, although ultrasonographic changes
consistent with mild pneumonic changes were present
within the cranioventral lung fields. It is possible that
impaired mucociliary clearance could have predisposed to
the development of pneumonia; this could also have
explained the hyperfibrinogenaemia identified when the
pony was first examined. However, these ultrasonographic
changes were detected 18 h after emergency placement of
a nasotracheal tube and therefore could be a result of
inhalational pneumonia secondary to the presence of the
tube. Dysphagia secondary to tracheal rupture and guttural
pouch empyema has been reported (Saulez et al.2005) and
EQUINE VETERINARY EDUCATION / AE / november 2008