Case No. :	59
Month :	November
Year :	2003
Contributor :	Dr. Hina Qureshi

Other Cases

A 17-year-old boy presented with fatigability & weakness in limbs, drooping of eyelids, nasal regurgitation of fluids & nasal twang
since four months. He also had a history of intermittent dyspnea on exertion. A provisional diagnosis of myasthenia gravis with
acute onset bulbar paresis was made. On examination, there was truncal, neck and eye closure muscle weakness. Motor power
was 4/5 proximally and 5/5 distally. Pulmonary function tests showed no improvement following neostigmine.


IMAGING FINDINGS:

The frontal chest radiograph showed a large antrerir mediastinal soft tissue mass on the right side adjacent to the heart.

Fig.1

A plain and contrast enhanced CT Chest showed a large, well defined, lobulated, anterior and superior mediastinal mass with
cystic components. There was no contrast enhancement. In view of the clinical presentation this lesion was thought to be thymoma.

Fig.2	Fig.3

At surgery, a multilobulated cystic mass was removed from the mediastinum.

Fig.4

On histopathology, the findings were characteristic of mixed cystic thymoma.

The patient had an uncomplicated post operative course.


DISCUSSION:

Thymic cysts account for 1-2% of all anterior mediastinal tumors. Patients are mostly asymptomatic unless the cysts are very
large or if hemorrhage occurs.

Etiology: These cysts probably result from developmental anomaly and represent persistent tubular remnants of the third
pharyngeal pouch, the fetal thymo-pharyngeal duct.

Pathophysiology: As they arise from the thymopharyngeal duct, these tumors can occur anywhere along the site of embryologic descent of the thymus - from mandible to the level of the diaphragm. Cysts are unilocular or multilocular and lined by squamous, transitional, simple cuboidal or columnar epithelium.

Imaging: Chest radiographs demonstrate mediastinal mass. Lesion appears to be cystic on CT and Ultrasound. MRI shows signal characteristics of water ie. hypointense on T1W & hyperintense on T2W images.

The differential diagnosis includes localised thymoma, teratoma, dermoid cyst, Hodgkins disease, Non Hodgkins lymphoma

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