CT/MRI Society Case of the Month
September 2006
Sponsored by Eklin Medical Systems
Patient Identification Number: CTMRSOC1
Patient Surname Code: CTMRSOC
Patient First Name Code: HATHCOCK
Accession Number: SEPTEMBER06
Contributor: John Hathcock
Contributor’s Affiliation: Auburn University College of Veterinary Medicine
Species: Canine
Breed: Labrador Retriever
Age at exam: 8 years
Gender: fe/s
Presenting signs and pertinent history:
2 year history of cerebellar signs
Clinical Findings:
Panting at rest. Slight dehydration. Moderately alert. Extremely ataxic. Difficulty rising after lying down. Severely disoriented and appeared as if balance was abnormal.
Neurological examination:
Head tilt to right. Truncal ataxia. Facial sensation, retractor bulbi reflex and blink reflex decreased on right side. Weak in all 4 limbs. Proprioception deficits in all limbs. Hypermetric, especially right foreleg. Vertical nystamus when placed in dorsal recumbency. Peripheral limb reflexes normal.
Relevant Laboratory data:
Primary clinical rule-out pre imaging:
Mass lesion in brain such as glioma or meningioma.
Modality: MRI
Manufacturer: Picker
Model/Field Strength: 1.0T
Sequences Acquired:
Proton density and T2 weighted spin echo transverse plane; FLAIR transverse plane; T1 weighted spin echo transverse and sagittal planes; post contrast T1 weighted spin echo transverse, sagittal and dorsal planes
CT/MR Findings:
There is a large, irregularly shaped mass in the caudal dorsal aspect of the cranial vault. This mass is primarily hypointense to brain on all sequences with irregular areas of mixed signal intensity. It is located mostly on the midline and extends rostroventrally from the caudodorsal aspect of the occipital bone to the level of the rostral brainstem. This mass is contiguous with the caudal aspect of the calvarium. The occipital bone in this area is irregularly shaped, ill-defined and has areas of increased signal. Additionally, the dorsal neck musculature caudal to the skull is asymmetric and contains multiple focal areas of increased signal. These areas also appear continuous with the abnormal occipital bone. There is severe compression and displacement of the cerebellum and brainstem in a ventral direction by the large mass with compression and deviation of the occipital lobes dorsally. Moderate dilation of the lateral ventricles, third ventricle and the rostral aspect of the fourth ventricle is present. On post-contrast images there is marked, inhomogenous contrast enhancement of the mass. The areas of the mass that were hypointense in pre-contrast images did not enhance.
Computed tomography was performed to assess bony extent.
There is a large non-homogeneous radiopaque mass associated with the caudodorsal aspect of the occipital bone. This mass has a coarse granular appearance and is roughly ovoid with smooth well-defined margins. There is invasion of this mass into the cranial vault with the majority of the mass being intracranial (measuring 3 x 3 x 3cm). The mass extends from the caudodorsal occipital region rostroventrally along the midline to the level of the tympanic bulla. There is significant compression of the caudal cerebrum, cerebellum and brainstem with moderate hydrocephalus present. There is also caudal extension of the mass into the dorsal neck musculature that appears multilobulated with a similar granular appearance.
CT/MR Assessment:
Large, contrast enhancing mass involving the occipital bone that extends into the cranial vault as well as into the neck musculature. These changes are suggestive of a neoplasia originating from bone such as multilobular tumor of bone or other primary bone tumor such as osteosarcoma or chondrosarcoma. The computed tomography characteristics of the lesion are compatible with multilobular tumor of bone.
Post Imaging Management:
Outcome:
Euthanasia. Histopathology examination found disorganized cartilage and bone surrounded by pleomorphic spindle cells separated by a variable eosinophilic matrix.
Final Diagnosis based on all diagnostic tests and outcome:
Multilobular Tumor of Bone (MLTB)
Comments:
Most of the time, I recommend CT to evaluate lumps and bumps arising from the calvarium. And in my experience MLTB is generally presented as such and has a characteristic appearance (and location) on CT images so that a preliminary diagnosis may be made. However, there was no report of a mass or abnormality in the soft tissues caudal to the calvarium in the physical examination in this case. Magnetic resonance imaging was chosen as the initial modality because of the severe neurological signs and the absence of mass arising from the calvarium. Once the large intracalvarial mass was identified contiguous with the mass caudal to the occipital bone, CT was done to evaluate mineralization characteristics.
References:
Lipsitz D, Levitski RE, Berry WL. Magnetic resonance imaging features of multilobular osteochondrosarcoma in 3 dogs. Vet Rad & US 42:14-19, 2001.
Hathcock JT, Newton JC. Computed tomographic characteristics of multilobular tumor of bone involving the cranium in 7 dogs and zygomatic arch in 2 dogs. Vet Rad & US 41:214-217, 2000.