Page 64 - Feline diagnostic imaging

60 5 Diagnostic Imaging of Diseases of the Skull
Fungal rhinitis, which in cats is most commonly due to concurrent ventral intracranial lymphoma represent direct
Cryptococcus spp. (Cryptococcus neoformans or C. gatti), regional extension of disease or are a form of multicentric
has a unique imaging appearance in that it affects the nasal lymphoma (Figure 5.12d–f) [57].
cavity, central nervous system or skin. The nasal form is Nasal adenocarcinomas have a more varied appearance
most common and the central nervous system (CNS) form due to the different forms, which include acinous, cystic,
is likely due to the nasal infection crossing the cribriform mucinous or papillary adenocarcinomas [54]. This influ-
plate (see also Chapter 6). Therefore, it is critical to evalu- ences their imaging appearance. Most are soft tissue
ate the nasal cavity for rhinosinusitis, and intranasal and/ attenuating masses on CT images with variable contrast
or intracranial nodules or fluid‐filled lesions [40, 41]. enhancement patterns, but generally all cause marked
Sinonasal aspergillosis is also a chronic presenting rhinitis, turbinate destruction (Figure 5.13) [37, 49]. The ability to
which may transition into sinoorbital aspergillosis, which distinguish nasal neoplasia from rhinitis is improved if
is a more severe form [42]. Both CT and MRI have been there is concurrent consideration of the appearance of the
used to evaluate the nasal passages for fungal infections or medial retropharyngeal lymph nodes [49]. Neoplasia is
to differentiate fungal infection from neoplasia. However, more likely if the hilar fatty area is abnormal in the lymph
the primary benefit has been in determining the best site nodes, asymmetry is present in the dorsal ventral dimen-
for diagnostic sampling [5, 34]. The CT features of fungal sion of the lymph nodes, and if the nodes have decreased
rhinitis include osteolysis of the paranasal bones and nasal heterogeneous attenuation prior to contrast administra-
turbinates, often bilateral space‐occupying soft tissue tion. Acinic nasal carcinomas cause masses with hetero-
masses with variable enhancement, and extension into the geneous hyperintense signal intensity in T2‐weighted
orbital or facial soft tissues [37, 38, 43]. The severe destruc- and short tau inversion recovery (STIR) MR images and
tive rhinitis seen in dogs with nasal fungal disease is undergo moderate peripheral enhancement [58]. Generally,
uncommon in cats [44]. Inflammatory rhinitis can also feline nasal adenocarcinomas are characterized in MR
result from nasal foreign bodies, and has been reported as images as possessing heterogeneous hyperintensity to
the third most common disease of the nasal cavity [45]. muscle in T2‐weighted images and undergoing moderate
Imaging case reports of rhinitis secondary to foreign mate- to marked contrast enhancement (Figure 5.14) [59].
rial include a nasopharyngeal trichobezoar, grass seed, Reports of these are most commonly associated with
tooth, or tooth fragment intrusion, needle, stone, and air intracranial invasion and these cats can present without
gun pellet [36, 46–48]. More focal lysis around the foreign sinonasal signs.
material is a feature, whereas there is more chronic nonde- Polyps are benign growths that more commonly affect
structive changes associated the nasal turbinates. feline patients than canine patients. Nasopharyngeal pol-
As has been discussed, the imaging appearance of nasal yps are most common, but otic and nasal polyps are also
neoplasia is similar to that reported for rhinitis and espe- reported [60]. These polyps are benign growths that origi-
cially chronic rhinitis [36, 43, 49]. It has been suggested nate from the tympanic bulla, eustachian tube or nasal epi-
that aggressive‐appearing unilateral lesions are more com- thelium [61]. Underlying inflammatory disease processes
monly neoplastic, but other studies have not identified this have been suggested as the cause of these growths, from
consistently [33, 37, 43]. The two most common forms of chronic viral infection or chronic middle ear or upper res-
feline intranasal neoplasia are adenocarcinoma and lym- piratory inflammation. They most commonly occur in
phoma [36, 49–51]. Squamous cell carcinomas are included young cats, with clinical signs depending on the location of
in cases involving the nasal planum and if there is deform- the polyp, such as otitis externa or nasal discharge, sterto-
ity of the facial bones. Less common neoplasms include rous breathing and sneezing most commonly. Diagnostic
adenomas, basal cell tumors, plasmacytomas, olfactory imaging plays a critical role in diagnosing these and
neuroblastoma, and intranasal sarcomas [51–55]. planning surgical approaches. Radiographs are the least
Nasal or nasopharyngeal lymphoma is a less common beneficial, unless the soft tissue mass is large enough and
form of feline lymphoma; some report it as the most com- extends into the nasopharynx sufficiently to be radio-
mon nasal cavity tumor and more common than other neo- graphically conspicuous on a lateral radiograph of the
plasms or inflammatory conditions [36, 54]. The appearance skull (Figure 5.15) [3, 62]. More commonly, the secondary
of lymphoma on CT includes contrast‐enhancing soft tissue effects of the polyp are identified radiographically, which
masses with extensive bone and nasal turbinate lysis, nasal include soft tissue opacification of the bulla or thickening
septal deviation or lysis and nonenhancing fluid in the of the bulla indicative of otitis media and/or sclerosis of
sinuses (Figure 5.12a–c) [37, 49, 56]. Lymphoma infiltrative the petrous bone suggestive of otitis interna.
lesions can affect the nasal cavity, nasopharynx or both. It Both CT and MRI are more routinely used to diagnosis
has been hypothesized that nasopharyngeal lymphoma and feline inflammatory polyps and/or distinguish these from