J Vet Intern Med 2007;21:535–538

Brainstem Abscess Due to Plant Foreign Body in a Dog
Isidro Mateo, Valentina Lorenzo, Alberto Muñoz, and Marti Pumarola
7-month-old male intact Dachshund was referredbecause of a 1-month history of ataxia, tetraparesis, and depressed mental status. Clinical signs wereprogressive until examination and remained static
afterwards. The dog had been treated with prednisonea(2 mg/kg body weight PO q24h) and vitamin B
complex.b Results of hematologic and serum biochemical analysis performed by the referring veterinarian
showed mild thrombocytopenia (142 3 103 platelets/mL;reference range, 170–530 3 103 platelets/mL) andneutrophilia (82%; reference range, 40–75%). Serum
antigen for Dirofilaria immitis and antibodies for
Ehrlichia canis and Borrelia burgdorferi were negative.
Hematologic and serum biochemical analysis performed
2 days before referral revealed increased protein concentration (8 g/dL; reference range, 5.7–7.7 g/dL) andtotal globulin (4.29 g/dL; reference range, 2–4 g/dL).
Other variables were within reference range. Serumpolymerase chain reaction for canine distemper virus
was negative. The dog was current on routine vaccination and no history of systemic disease was noticed by
the owner, except for sporadic neck pain.
No abnormalities were detected on physical examination. Neurologic examination revealed depressed
mental status, spastic tetraparesis, and ataxia, withpelvic limbs more affected. Abnormalities on postural
reactions included absent hopping reaction on thethoracic limbs and decreased extensor postural thrustreaction. Hopping reaction on pelvic limbs and all spinal
reflexes were normal. Cranial nerve deficits included
depressed menace reaction on both sides, although more
severe on the right eye, and bilateral decrease on
palpebral reflex. There was no visual impairment.
Neuroanatomic lesion localization was considered focal
in the pons and medulla. The depressed menace reaction
could be attributed to the depressed mental status and/or facial paresis.
Magnetic resonance imaging (MRI) study of thebrain and cervical spinal cord was performed using
a superconductive magnet operating in 0.5 T.c Anesthe-A

From the Resonancia Magnética Veterinaria, Madrid, Spain(Mateo, Lorenzo, Muñoz); the Departamento de Neurorradiologia,Hospital 12 de octubre, Madrid, Spain (Muñoz); and the Departament of Animal Medicine and Surgery, Veterinary Faculty,
Universitat Autónoma de Barcelona, 08193 Bellaterra (Cerdanyoladel Vallés), Barcelona, Spain (Pumarola). The work was done at theResonancia Magnética Veterinaria, Madrid, Spain. Previously
presented at the ESVN 19th Annual Symposium held in Barcelona,Spain, September 2006.
Reprint requests: Isidro Mateo, DVM, C/ Arturo Soria 320 13uB,28033-Madrid, Spain; e-mail: isidro_mateo@yahoo.es.
Submitted October 25, 2006; Revised November 7, 2006;
Accepted December 6, 2006.
Copyright E 2007 by the American College of Veterinary Internal
Medicine
0891-6640/07/2103-0026/$3.00/0

sia was induced with propofold (6 mg/kg body weight)
and maintained with isofluoranee until the end of theprocedure. MRI study included T1-weighted spin echo(SE) sequences (500/14; repetition time [TR]/echo time[TE]), T2-weighted fast spin echo sequences (4000/110/16; TR/TE/echo train), and gadolinium-dimeglumide enhanced T1-weighted SE sequences in the 3orthogonal planes (gadolinium chelatef dose was0.1 mMol/kg, IV).
The study revealed the presence of a focal swellingwith prolongation of T1 and T2 relaxation rates in themedulla (Fig 1). An intra-axial round mass was localized
in the center of the medulla. The lesion induced changes
related to vasogenic edema, corresponding with hypointensity on T1-weighted images and hyperintensity on
T2-weighted images. The mass enhanced heterogeneously in the periphery on T1-weighted postcontrast images.
Mild dilation of the ventricular system, probably related
to obstruction of the cerebrospinal fluid (CSF) flowcaused by the lesion, was also present. On the basis of
the MRI findings, the main differential diagnoses
included neoplasm (diffuse glioma) and abscess. Becauseof the poor prognosis the animal was humanely
euthanized.
On necropsy, no abnormalities were found apart fromcongestion on the entire brain, which was fixed in 10%
buffered formalin and paraffin embedded. Sections 4mm thick were obtained with a sliding microtome andstained with hematoxylin and eosin and Massontrichrome. Microscopic examination of the brainstem
identified a focal pyogranulomatous reaction andassociated areas of malacia with severe inflammatory
reaction, localized ventrolaterally in the medulla oblongata (Fig 2A). Plant material, together with necrotic
debris, was acting as a foreign body, surrounded bya thick wall formed by a proliferation of fusiform cells
and abundant collagen fibers, together with inflammatory cells (neutrophils and macrophages) (Fig 2B).
Masson trichromic stain revealed expanded connective
tissue constituting a capsule around the plant material
previously described. This inflammatory reaction wasassociated with numerous gitter cells, neutrophils,
lymphocytes, and plasma cells. Chromatolytic andpicnotic neurons, spheroids, diffuse spongiosis, andgliosis were observed in the adjacent parenchyma.
Final diagnosis was a caudal brainstem abscessbecause of migrating plant foreign body. Migration ofplant material is a frequent problem in veterinary
medicine, most often involving the external ear canal,
oral and nasal cavities, interdigital web, and nictitating
membrane.1 Thus, a wide variety of symptoms could beseen, depending on where the inflammation is produced.
In most cases, abscesses are located in the dermis, butthey can be sporadically detected practically everywherein the body, because of the capability of the grass awn tomigrate. Signs can be attributable to vertebral osteomy-

536

Mateo et alelitis and discospondylitis,2 granulomatous pleuritis,3 orperitonitis,3 among others.
Foreign body granulomas in the brain of dogs andcats have been reported sporadically in the literature.4–8
This dog had a plant foreign body granuloma in themedulla oblongata that was imaged on magneticresonance. A review of the literature revealed that someother cases of intracranial foreign bodies, vegetable andnonvegetable, have been described, but in different
locations. A porcupine quill in a Saint Bernard waslocalized in the occipital lobe of the left cerebral
hemisphere. The quill probably penetrated into thecranial cavity through the foramen magnum.4 A sewing
needle penetrated the pharyngeal soft tissue and the baseof the cranium and was localized in the left pyriform
lobe5 in a cross-breed adult dog.
Few cases of brain neurologic lesions attributable tomigrating plant material have been described in small
animals; however, the migration route is usually notelucidated. In one dog plant material was localized in theright lateral and third ventricles, probably after a periocular pathway.6 In the other dog a grass awn was locatedin the ventrolateral aspect of the right occipital lobe,
internal capsule, and rostral horn of the lateral ventricle,
suggesting migration through the ventral aspect of thecranium.6 In the latter dog, plant material was localizedwithin the dura overlying the occipital lobe; themigration route probably involved the foramen magnum.6 Pyogranulomatous otitis media/interna withosteomyelitis causing pyogranulomatous meningoencephalitis in 2 dogs and 1 cat was associated withintrathecal plant material, suggesting that this material(a foxtail) could have migrated through the ear canalinto the tympanic cavity and finally into the brain,
possibly through the internal acoustic meatus.7 A cat
with brain abscess in the right thalamic nuclei because ofa migrating foxtail from the nasal cavities through thecribiform plate to the encephalon has also been described.8 Presence of grass awn in nasopharyngeal
localization has been previously reported in cats.9
Foreign bodies from nasal cavities causing brain damage
have also been reported.10 Intracranial penetrating
injuries via optic canal are relatively frequent in human
medicine, and they are often caused by chopsticks.11–13
The migration route in the current dog remains
obscure because no lesions were evident on physicalexamination or on postmortem studies. We suspect thatthe foreign body could have penetrated throughpharyngeal tissues directly to the space between therFig 1. Magnetic resonance images of the brain. (A) Sagittal spinecho (SE) T1-weighted image. Note the enlargement of the medulla
and low signal intensity (T1 relaxation time prolongation). (B)
Sagittal fast spin echo (FSE) T2-weighted image. Note theenlargement of the medulla and diffuse signal intensity (T2relaxation time prolongation). (C) Transverse FSE T2-weighted
image through the medulla shows asymmetric enlargement, highsignal intensity, and edema. (D) Postcontrast dorsal SE T1weighted through the medulla shows the lesions with central core
nodular enhancement.

Intracranial Foreign Body in a Dog

537

Fig 2. Histopathologic study. (A) Brain abscess at the level of the medulla oblongata showing the inflammatory reaction associated withthe vegetal foreign body granuloma. Hematoxylin and eosin. Bar 5 500 mm. (B) Detail of Figure 2A. Notice the connective tissue
constituting a capsule around the vegetal tissue, which is surrounded by inflammatory cells (neutrophils and macrophages). Hematoxylinand eosin. Bar 5 100 mm.

occiput and atlas, therefore migrating cranially to thebrainstem. This same migration pattern has beensuggested before in a case of a plant material granuloma
involving a lesion in the junction between the medulla
oblongata and first cervical segment.14 Pharyngeal
injuries are recognized sporadically, especially in medium and large breed dogs.15,16 They may produce
neurologic involvement affecting the spinal cord causing
osteomyelitis17 and discospondylitis with subsequentneck pain, gait abnormalities, and other neurologic
deficits,14,17–20
Intracranial abscesses in humans generally havea hematogenous source and have been classified into 4
different stages as determined by MRI features and thetime the abscess was formed. Early and late cerebritis
and early and late abscess formation are the 4 progressive stages, although there is a gradual evolution in
the phase of infection and host response. Early
cerebritis, corresponding to stage 1, may show different
T1 signal intensities, ill-defined high T2, and poorly
defined enhancement because of the blood-brain barrier
disruption. Later, in stage 2, central necrosis andformation of a capsule with neovascularization occur,resulting in a ring-enhancing lesion. MRI shows
irregular periphery with iso- to high-signal on T1 andcentral high T2 core with peripheral enhancement on
postcontrast sequences. Early abscess formation, or
stage 3, which corresponds to early capsule formation,
may show thin rim, high intensity on T1, very low
intensity on T2, and intense enhancement. A capsule ofdecreased signal intensity in T2 sequence is not usuallyseen in tumors. The decreased signal intensity is causedby paramagnetic free radicals within phagocytic macrophages.21 Late abscess, stage 4, which corresponds tolate capsule formation, may show marked surrounding
high T2-intensity edema, contraction of the core,irregular inner margin of rim, enhancement of rim,and parts of the core.22 The length of time required toform a mature abscess varies from 2 weeks to severalmonths.
The chronicity of clinical signs in the dog in this casereport suggests stage 4 brain abscessation or late capsulestage. Nevertheless, not all the classic MRI features
expected, such as capsular enhancement, were present,
probably because of the unusual structure of theinflammatory process, namely foreign body core, whichmimicked the features of a granuloma. Also, someabscesses may resemble primary or secondary neoplasm,
and this differential diagnosis was considered. New MRItechniques, such as difussion-weighted imaging andproton magnetic resonance spectroscopy, are invaluable
for accurate diagnosis in such cases.22 Notwithstanding,conventional MRI has proved to be a highly sensitiveand specific method to detect inflammatory lesions in
the brain parenchyma.
CSF collection might have been useful to differentiate
inflammatory disease from neoplasia. In this case,however, because of the encapsulated nature of thelesion, CSF would likely have been nondiagnostic.
Besides, cellularity and culture in central nervous
systems bacterial infections are often unrewarding in
the chronic stage.23
Brain abscesses can be initiated from different routes
and usually microorganisms reach the brain parenchyma
as a result of contiguous infection (otitis media/interna,
nasal sinuses infections), hematogenous disseminationor head injury.24 The most frequent microorganisms
isolated from lesions because of migrating plant material
are Streptococccus sp., Staphylococcus aureus, Pasteurella multocida, Actinomyces sp., and Nocardia sp.1
Moreover, clinical symptoms may not present forseveral days, months, or even years after an injury.12,13,23
This condition should be taken into account when signsof focal brain lesion are present together with compatible features in MRI, particularly for the medical andsurgical implications.

538

Mateo et alFootnotesaDacortin comp. 5 mg, Merck Farma y Quı́mica, SA, 08100
Mollet del Vallés (Barcelona), SpainbNervobión caps., Merck Farma y Quı́mica, SA, 08100 Mollet delVallés (Barcelona), Spainc
Gyroscan T5-NT, Philips. The Netherlands
dPropofol-Lipuro 1%, B. Braun Melsungen AG, D-34209 Melsungen, Germany
eIsoba Vet, Schering-Plough, SA, 28750 San Agustin de Guadalix(Madrid), Spainf
Magnograf 0.5 mmol/ml solución inyectable. Schering España,SA, 28045 Madrid, Spain

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