A 64-year-old male presents with a left sided neck mass that he had noticed one month ago. On ultrasonographic examination, the mass was 4.3 x 3.3 x 2.2 cm with heterogeneous appearance. An ultrasound guided needle biopsy was performed and displayed malignant cells compatible with metastatic squamous cell carcinoma. A p16 immunostain was strongly positive, high risk human papillomavirus (HPV) E6/E7 mRNA in-situ hybridization was equivocal. A follow up 18F-fluorodeoxyglucose (FDG) PET/CT showed uptake in the left cervical level II lymph node, and symmetric mild uptake in bilateral palatine tonsils. A transoral robotic tonsillectomy and base of tongue resection was performed to localize the site of primary. A firm fibrotic area was noted in the left tonsil on palpation and cut surface. A representative frozen section was taken:
1. Which of the following is most likely representative of the finding on frozen section?
2. What is the most common cartilage producing parapharyngeal space tumor?
Cartilaginous choristoma
Cartilaginous choristomas, described as early as 1890 by Berry in tongue, are uncommon deep-seated proliferations of normal appearing cartilage. These often have significant fibrosis as seen here, prompting the alternative classification as chondroid metaplasia. Etiologically, this is likely incorrect as the cartilage typically appears mature with a well-formed perichondrium and without dystrophic calcification. In tonsil, despite the proximity to lymphoid stroma, cartilaginous choristomas are not particularly inflamed. The prevalence of cartilaginous choristoma in the tonsil is likely underreported since non-neoplastic tonsils are only representatively submitted for histologic evaluation but one prospective study indicates a prevalence of ectopic cartilage in tonsil specimens being as high as 6%. The incidental occurrence on intraoperative examination represents a modern phenomenon that can attributed to the advent of transoral robotic surgery (TORS) for the diagnosis and treatment of oropharyngeal squamous cell carcinoma. This case may also very well be the only gross photo documentation of a cartilaginous choristoma, albeit on a frozen section block.
The terms choristoma and hamartoma are often grouped together as developmental anomalies, however strictly speaking, choristomas are benign growths consisting of normal tissue in locations where the tissue is not normally found (ectopic). In comparison, hamartomas are benign growths of mature cells in their normal location, but in a disorganized manner. Neoplasms may occasionally enter the differential diagnosis for cartilaginous choristoma but are usually much larger and are distinguished by the presence of other elements. The more common tumor type with cartilaginous elements in the parapharyngeal space (and most common overall) is pleomorphic adenoma. However, with adequate sampling the transition to the typical admixture of ducts and myoepithelial cells will be recognized. Primary cartilaginous neoplasms (chondrosarcoma, chondroma) are theoretical considerations as well. Teratomas may have normal cartilage but are germ cell neoplasms with other elements.
Incidental findings such as cartilaginous choristoma in the context of intraoperative assessment of tonsils to find an occult primary will most assuredly be more common as the use of transoral robotic surgery becomes more widespread. Frozen section evaluation of TORS specimens is commonly utilized for diagnosis and margin assessment. While current ASCO recommendations are to submit TORS specimens in their entirety for frozen section, realistically this is not always feasible nor is it desirable given the risk of damaging or cutting through tumor. Accuracy of frozen section for identifying primaries is variable (50-90%) and can be skewed by inclusion of grossly obvious tumors to inflate performance. Here, the entire specimen consisted of four blocks and would not have been challenging to freeze in toto, but the multidisciplinary decision was to examine a representative section with the intent to preserve the remainder for higher quality permanent sections. Ironically, the discontiguous foci of tumor spanning 5 mm in this case were identified in a non-fibrous area on permanent sections. Whether they would have been identified or cut through if the entire specimen were frozen is speculative.
References
- Berry J., Fibrochondroma of the tongue, Trans Pathol Soc Lond. 1890; 41: 81
- Kannar V, Prabhakar K, Shalini S. Cartilaginous choristoma of tonsil: A hidden clinical entity. J Oral Maxillofac Pathol. 2013;17:292–3.
- Arora S, Agrawal M, Nazmi M, Kapoor NK. Histological study of routine tonsillectomy specimen. Indian J Otolaryngol Head Neck Surg. 2008 Dec;60(4):309-13.
- Çiriş IM, Erkılınc G, Kursat Bozkurt K, Karahan N, Yasan H, Sivrice ME. Cartilaginous choristomas in tonsillectomy specimen: A prospective analysis. Int J Pediatr Otorhinolaryngol. 2019 Jul;122:191-195.
- Maghami E, Ismaila N, Alvarez A, Chernock R, Duvvuri U, Geiger J, Gross N, Haughey B, Paul D, Rodriguez C, Sher D, Stambuk HE, Waldron J, Witek M, Caudell J. Diagnosis and Management of Squamous Cell Carcinoma of Unknown Primary in the Head and Neck: ASCO Guideline. J Clin Oncol. 2020 Aug 1;38(22):2570-2596. doi: 10.1200/JCO.20.00275. Epub 2020 Apr 23. PMID: 32324430.
Quiz Answers
Q1 = C. Choristoma
Q2 = A. Pleomorphic adenoma
Raja R. Seethala, MD
Professor of Pathology and Otolaryngology
University of Pittsburgh Medical Center
