MEDIASTINAL CYSTSJames Montgomery, DVMNovember 3, 2008

Mediastinal cysts

Infrequently occur Congenital or idiopathic Origin:

Pleural Branchial Parathyroid Thyroglossal Lymphatic Bronchogenic Thymic

Clinical signs

Generally none

Respiratory difficulty Space occupying

Patient ID: 132472

Allie 9 year old Spayed female Domestic shorthair

Weight loss, lethargy

Radiographs - 106076

Radiographs - 106076

Radiographs - 106076

Differential diagnoses

Abscess Granuloma Lymphadenopathy Hematoma Ectopic thyroid tissue Cyst Neoplasia

Lymphosarcoma, thymoma

Ultrasound - 106086

Ultrasound - 106086

Ultrasound - 106086

Aspirated 8mL golden brown fluid Cytology: WBC=200/ul; Protein=0.3 g/dl.

Extremely low cellularity. Contains only rare erythrocytes and debris.

No etiologic agents observed Interpretation: Low cellularity, low protein

fluid.

Consistent with idiopathic mediastinal cyst

Treatment options

In the absence of respiratory signs, intervention is not warranted (Zekas LJ, Adams WM. Vet Radiol Ultrasound 2002;43:413-8) Generally considered an incidental finding

Surgical removal Functional cysts (parathyroid) Space-occupying disease

Tracheal or vascular compression

Differentiating cysts

Histologic evaluation needed

Clinical findings: Thymic branchial cysts

Dyspnea, pleural effusion, aspiration of mucinous fluid

Multicystic appearance Thymic branchial cysts Lymphangiomas Cystic thymomas

Embryology

4 embryologic pharyngeal pouches Abnormal development may lead to formation

of cystic structures in the neck and cranial mediastinum

1st – Eustachian tube (middle ear) 2nd – Supratonsillar fossa

Branchial cysts 3rd – Thymus and cranial parathyroid glands 4th – Caudal parathyroid glands &

contributes to thyroid gland formation Thyroglossal cysts – abnormal development

near site of origin of the thyroid diverticulum

Summary

Opacities in the cranial mediastinum on thoracic radiographs should be investigated

Ultrasonographic identification of an anechoic mass with clear fluid supports diagnosis of mediastinal cyst

Majority of feline cranial mediastinal cysts are benign with no need for treatment

References

Ellison GW, et al. Idiopathic mediastinal cyst in a cat. Vet Radiol Ultrasound 1994;35:347-9.

Moore LE, Biller DS. Mediastinal disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 6th ed (St. Louis, MO: Elsevier Saunders, 2005) pp. 1268-9.

Swainson SW, et al. Radiographic diagnosis: mediastinal parathyroid cyst in a cat. Vet Radiol Ultrasound 2000;41:41-3.

Zekas LJ, Adams WM. Cranial mediastinal cysts in nine cats. Vet Radiol Ultrasound 2002;43:413-8.