Morphological changes in canine trachea after freezing

Cryonecrosis of normal bone is followed by repair of the defect by regeneration of bone from the periosteum and endosteum 2. Similar results have been observed after freezing of malignant cells invading bone 4. Since regeneration of bone and cartilage are similar, the possibility of regeneration of cartilage after destruction of a local area by freezing is suggested. Reconstructive problems make excision of some tracheal tumors hazardous or unacceptable. If freezing does not permanently impair the architecture of the trachea, it may offer a method of controlling or eradicating neoplasms which invade or arise from the trachea. Mongrel dogs each underwent an operation to allow the application of a cryoprobe to the external surface of the trachea. Sixty per cent of the circumference of three tracheal rings was frozen by repeated applications of the cryoprobe, each for a period of 5 min, to the anterior and lateral surfaces of the trachea. After freezing, two animals were sacrificed at each of several intervals varying from 5 min to 6 weeks. Necropsy examinations were performed on all animals. The mucosal response of trachea to freezing included gross evidence of ulceration within 6 hrs, histological evidence of beginning reepithelialization at 72 hrs, and complete healing after 2 weeks. Changes in connective tissue and vascular elements were apparent for 2 to 3 weeks after freezing. Cryonecrosis and subsequent repair of the tracheal cartilage lagged behind the sequential changes described for the mucosa and connective tissue. Although subtle changes in the staining characteristics of cartilage occurred within 6 hrs, absence of chondrocytes in the area of maximum freezing was not seen until 24 hrs. Fragmentation of cartilage did not occur until 72 hrs and was not maximal until 5 days. Healing of cartilage was first apparent after 2 weeks, and chondrocytes reappeared between 2 and 4 weeks after freezing. The most striking observation was the remarkable return of frozen cartilage to a near normal form and appearance. The progressive return from destruction of all layers to an essentially normal tracheal architecture suggested that the cryoprobe may be of value in the management of some tracheal tumors.