Trigeminal nerve sheath tumor

sv penchevDr Svetoslav Penchev

United  Veterinary Clinic

Varna, Bulgaria

 

 

The nerve sheath is a layer of myelin and connective tissue that surrounds and insulates fibers in the peripheral nerves. A nerve sheath tumor is an abnormal growth within the cells of this covering. Nerve sheath tumors include schwannomas, neurilemmomas, and neurofibromas. The trigeminal nerve is the most frequently affected cranial nerve. This results in unilateral atrophy of the temporalis and masseter muscles and facial dysesthesia or anesthesia. Eventually, brain-stem compression can develop.

 

 

Signalmen: 12 years old, female, castrated Labrador retriever

 

History:  The owner noticed that dog`s head has not normal shape.

 

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Case presenting signs:  Chronic right trigeminal nerve deficit with atrophy of the temporalis and masseter muscles. Reduced facial sensation, absent palpebral reflex with normal menace response reaction and reduced right corneal sensation and enophtalmus.

 

Clinical examination: The overall condition of the dog was normal with normal appetite, good muscle and body condition except the right temporalis and masseter muscles.  Internal body temperature 38,8 ; Normal respiratory and heart rate; Color of mucous membranes – pink; CRT – 1,5 sec.

 

Neurological examination:

Mentation and behavior- Normal

Posture- Normal

Gait – Normal

Cranial nerves – right trigeminal nerve deficit

There was no change in conscious proprioception and bladder function was normal.

Spinal reflexes were normal.

 

Neuroanatomic localization: R Trigeminal nerve

 

Differential diagnosis:

Idiopatic/Inflammatory/Trauma/Metabolic/Neoplastic

 

Case work-up:  CBC – without changes; Biochemistry – Elevation of Liver enzymes (ASAT 69 IU/L; ALAT 90 IU/L)

Contrast MRI study of the head was performed with GE MRI 1.5 Tesla.

 

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MRI     findings:

There is a large extra-axial T1 hypointense, T2 hyperintense tubular mass that arises at the origin of the right trigeminal nerve and extends rostrally through the trigeminal canal of the temporal bone. The right oval foramen is enlarged because of involving the mandibular branch. Atrophy and denervation of the masticatory muscles (temporalis, masseter and pterygoid muscles) is present with T1-, T2-hyperintesity, reduction of the muscle mass and replacement by fatty tissue. Post contrast images shows marked contrast enhancement of the right trigeminal nerve compared with the left (mild enhancement of the left trigeminal nerve is physiologic).

 

Diagnosis:

Right Trigeminal nerve sheath tumor

 

Intracranial peripheral nerve sheath tumors are relatively uncommon tumors in dogs. Clinically, dogs with intracranial PNST have one or more of the following clinical signs: ipsilateral masticatory muscle atrophy, loss of facial sensation, and Horner’s syndrome. Signs from intracranial brainstem compression can also occur. Radiation therapy is a commonly used modality in the treatment of intracranial PNST. Stereotactic radiation therapy (SRT) is one method used to deliver a curative dose of external beam radiation therapy. This precise and conformal treatment directly targets the radiation at the tumor with rapid dose drop-off, which allows for very high doses of radiation to be administered without increasing toxicity to adjacent normal tissues.

Cerebrovascular accidents in dog

 

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Dr Svetoslav Penchev

United Veterinary Clinic

Varna,Bulgaria

 

 

Stroke or cerebrovascular accident (CVA) is the most common clinical manifestation of cerebrovascular disease, and can be broadly divided into ischemic stroke and hemorrhagic stroke. CVA are characterized clinically by a per acute or acute onset of focal, asymmetrical and non-progressive brain dysfunction. Next cases show the both type of CVA in dogs.

1st case is about 9 years old female boxer. The dog was referring to the clinic with acute onset of seizures. The results of CBC and Biochemistry were normal and MRI was performed.

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MRI findings: Intra-axial right piriform lobe and hippocampus lesion with impression of moderate swelling of these portions is present. The cerebral falx is only mildly displaced to the left. There is corresponding low T1 signal intensity in these sections of the brain suggesting edema. There is no enhancement of the lesion after contrast administration. The findings suggest that there is a non-hemorrhagic cerebrovascular accident in right forebrain of the dog.

 

The 2nd case is about  a 8 years old male Cane corso. The dog was present in the clinic with unilateral fore brain deficits and history of epileptic seizures. Biochemistry and CBC were normal and MRI was performed.

 

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MRI findings : There is a well‐delineated T1 iso- to hypointense  and T2 hypointense  mass lesion with surrounding brain edema in right piriform lobe with a thin peripheral rim of contrast enhancement. There is a mass effect, displacement of the right lateral ventricle and midline shift to the left. This imaging feature is consistent with an acute to subacute intracranial hemorrhage.

 

Conclusion:

MRI features of Hemorrhagic infarction in dogs may not be distinguishable from hematoma caused by vascular disruption. Imaging characteristics will vary depending on the size, location, and chronicity ofthe hematoma.

Hyperacute – 24 hours   T1 isointense ; T2 hyperintense

Acute         1-3 days  T1 iso- to hypointense  ; T2 hyperintense

Early subacute   >3 days  T1 hyperintense  ; T2 hypointense

Late subacute    >7 days  T1 hyperintense ; T2 hyperintense

Chronic              > 14 days   T1 hypointense ; T2 hypointense

Secondary  features :  mass effect, surrounding edema, midline shift , ventricular displacement and compression .

 

MRI features of Nonhemorrhagic Infarction in dogs include mildly T1 hypointense and T2 hyperintense  lesion with minimal  mass effect involving both gray and white matter on unenhanced MR images. These changes seen in ischemic parenchyma rely on an increase in tissue water content. Gradually, during the acute stage, the T2-weighted image becomes more hyperintense in the ischemic region, particularly over the first 24 hours. These signal changes seen in the first 24-hours are best appreciated in grey matter and are well visualized in deep grey matter structures such as the thalamus or basal ganglia, in addition to cortical grey matter. Gadolinium enhances infarcts because of vascular rupture but does not enhance ischemia or edema.