Radiol Oncol 2023; 57(4): 430-435. doi: 10.2478/raon-2023-0045 430 review Retropharyngeal calcific tendinitis in the neurological emergency unit, report of three cases and review of the literature Tatjana Filipovic 1 , Jernej Avsenik 2 1 Institute of Clinical Neurophysiology, Division of Neurology, University Medical Centre, Ljubljana, Slovenia 2 Institute of Radiology, University Medical Centre, Ljubljana, Slovenia Radiol Oncol 2023; 57(4): 430-435. Received 4 July 2023 Accepted 17 August 2023 Correspondence to: Tatjana Filipović, M.D., Ph.D., Institute of Clinical Neurophysiology, University Medical Centre, 1000 Ljubljana, Zaloška cesta 7, SI-1000 Ljubljana, Slovenia. E-mail: tatjana.filipovic@kclj.si Disclosure: No potential conflicts of interest were disclosed. This is an open access article distributed under the terms of the CC-BY license (https://creativecommons.org/licenses/by/4.0/). Background. Retropharyngeal calcific tendinitis (RCT) is a relatively benign condition of calcination of the longus colli muscle tendon of unknown origin, which causes severe acute neck pain. However, it is often not recognised, which leads to delayed diagnosis and unnecessary treatment. Patients and methods. We have searched PubMed and Google Scholar for publications which reported at least one patient with RCT and were published in the last 20 years. The literature was then analysed according to the PRISMA-S protocol. We also report three patients with RCT presenting at the Neurological Emergency Unit, University Medical Centre, Ljubljana, Slovenia, from 1 January 2020 to 1 June 2022. We discuss their clinical presentation and differential diagnosis, explain our decision-making process, and briefly describe the clinical course. Case reports have been performed according to the CARE protocol. Results. We have analysed a total of 112 titles with 231 patients. The most frequent symptoms and signs were: neck pain, neck stiffness and odynophagia, as was the case in our reported cases. Conclusions. RCT is a dramatic yet self-limiting condition, often not recognised in time. An effort should be made to increase neurologists’ awareness about this condition. Key words: retropharyngeal calcific tendinitis Introduction Calcifications in the retropharyngeal space as a cause of severe acute head and neck pain have long been recognised, but have only recently been incor- porated in the latest (3 rd ) International Classification of Headache Disorders (ICHD-3). Retropharyngeal calcific tendinitis (RCT) is, according to ICHD-3 cri- teria, a “headache caused by inflammation or calci- fication in the retropharyngeal soft tissues”. 1 It oc- curs as a result of poorly understood mechanisms in the upper fibres of the longus colli muscle. Data from a similar condition affecting the shoulder joint showed neovascularisation and new nerve growth as a result of the innate immune response. 2 This often dramatic but self-limiting condition is often not recognised among physicians, which leads to unnecessary diagnostic procedures and delayed treatment. 3,4 Besides neurologists, other specialists are also involved in treatment of this condition, es- pecially otorhinolaryngologists (ENT) 3,4 and ortho- paedic surgeons. 5 The annual incidence of RCT is estimated to be from 0.5 cases per 100 000, up to 1.1 case per 1000. 4,6 The aim of the present study was to review the literature data and present our own experience with RCT in order to increase neurologists’ aware- ness about the condition. Radiol Oncol 2023; 57(4): 430-435. Filipovic T and Avsenik J / Retropharyngeal calcific tendinitis review 431 Patients and methods On 7 September 2022 we have searched the PubMed and Google Scholar with the keywords “retropharyngeal calcific tendinitis”, “longus colli tendinitis” and “acute neck pain”. The search was conducted for the titles published in the last 20 years (2002–2022). The analysis of the literature was performed according to the PRISMA-S proto- col. 7 We analysed the frequency of reports of RCT regarding the facility where patients were first registered and treated. In addition, we report three cases of ret- ropharyngeal calcific tendinitis (RCT) that were referred to the Neurological Emergency Unit (NEU), Division of Neurology, University Medical Centre Ljubljana, Slovenia, from 1 January 2020 to 1 June 2022. The reports follow the CARE proto- col. 8 Patients NEU is a tertiary medical facility for over 300 000 inhabitants where 25 016 patients were exam- ined in the time period described above, of which 2073 were discharged with the main diagnosis “Headache, unspecified” (G 44.8 or R 51) accord- ing to ICD-10 and only three were diagnosed with RCT (M 65.2). Patient 1 A previously healthy 40-year-old female with sus- pected meningitis was referred to our institution in November 2020. She was experiencing excru- ciating throbbing neck pain, which had devel- oped spontaneously within 12 hours without any trauma or heavy mechanical load. She complained that swallowing was painful and that the pain in- creased with any attempt to move the head. A neu- rological exam showed severe neck stiffness with immobility in all directions as well as dysesthesia over the vertex and occipital regions. Laboratory workup revealed only mildly increased C reactive protein (CRP) of 20 mg/l (normal value < 5 mg/l) and white blood cell count (WBC) of 10.2 (normal < 10x10 9 /l). Although the patient was afebrile, the re- tropharyngeal abscess was still considered in the differential diagnosis. Magnetic resonance imag- ing (MRI) of the neck showed fluid collection and swelling in the cranial part of the longus capitis/ colli muscle on the left (Figure 1). A lumbar punc- ture was also performed, but the CSF was normal. She was treated in the NEU and discharged with ketoprofen 200 mg daily and a soft neck collar. The pain resolved in one month. Patient 2 A 51-year-old female with a history of arterial hy- pertension was referred to the NEU in November 2021 with clinical suspicion of meningitis. Five days prior to referral, she experienced a sudden mild pain in the right posterior neck, radiating to the occipital region. In the following three days, the pain became unbearable. It increased during swallowing and with eye movements. Due to the chronic neck pain, the patient had an MRI of the neck 9 months prior to the examination. Broad- based protrusions of the C5/6 and C6/7 interver- tebral discs without compromise of neural struc- tures were described, but no other abnormalities FIGURE 1. MRI in a 40-year-old female showed short tau inversion recovery sequence (STIR) hyperintensity in the upper part of her left Longus colli muscle, suggesting an oedema (A), with thin prevertebral effusion on sagittal images (B). After intravenous gadolinium contrast injection, a small area of enhancement was observed in the medial aspect of the muscle (C), but no peripherally enhancing collection to suggest an abscess was present. Diffusion-weighted imaging was normal, excluding the presence of pus (D). A B C D Radiol Oncol 2023; 57(4): 430-435. Filipovic T and Avsenik J / Retropharyngeal calcific tendinitis review 432 were noted at the time. She was afebrile at pres- entation. A neurological exam showed limited mobility of the neck and reduced light touch sense over the right lower extremity. Laboratory workup was normal. Head CT and computed tomography angiography (CTA) of the aortocervical and intracranial vessels revealed no vascular abnormalities. MRI of the cervical spine revealed prevertebral oedema from the C1 to the C4 level (Figure 2), not seen on previous MRIs. In addition, calcifications in front of the C1 arc on CTA was noted. The patient had been treated three days in the hospital and discharged with ibupro- fen, 1800 mg daily. The pain gradually subsided over the next two months. The sensory distur- bance over the left leg remained unexplained. Patient 3 In May 2022, a previously healthy 43-year-old female experienced pain in the right posterior neck which evolved gradually over a period of 48 hours. She described an electric shock-like pain that was radiating to the occipital area at any at- tempt of head extension, and even if she tried to hold the head in the neutral position. Laboratory workup at the Medical Emergency Unit revealed only slightly elevated CRP. Pain medication (met- amizole 2.5 g IV) was minimally effective. Three days after the onset of pain the patient was ex- amined at the NEU where occipital neuralgia was suspected, and outpatient MRI of the head and neck was suggested. As the pain continued, she came to the NEU on day 5 and spondylodiscitis was added to differential diagnosis. A neck CT revealed calcifications in the region of alar liga- ments and repeated laboratory results showed el- evated CRP of 20 mg/l (normal < 5 mg/l), with no other abnormalities. The patient was discharged with ibuprofen 1200 mg daily. As the pain con- tinued without relief, she returned to the NEU on day 7. This time RCT was diagnosed and a short course of corticosteroids was prescribed (dexa- FIGURE 2. STIR (short tau inversion recovery) imaging in sagittal (A) and axial (B) plane demonstrated prevertebral soft tissue swelling and oedema in a 51-year- old female, suggesting retropharyngeal calcific tendinitis as the underlying cause. Calcifications in the medial aspect of the longus colli muscle in front of the C1 arc were noted on computed tomography angiography (CTA) (C), confirming the diagnosis. A B C TABLE 1. Results from literature analysis N % SPECIALITY REPORTS 112 100 Otorhinolaryngology (ENT) 32 28.6 Emergency medicine 26 23.2 Orthopaedic surgery 24 21.4 Other 19 17 Neurology 11 9.8 PATIENTS TOTAL 231 100 Sex: women:men 121:110 52.4:47.6 Age (years) Median 22–78 46.7 No comorbidities 224 96 Acute onset (24–72 hours) 208 91 LEADING SYMPTOMS Neck pain 231 100 Neck immobility 222 96 Odynophagia 210 91 Trismus 35 15 Torticollis 11 5 Stridor 1 0.4 Dysarthria 1 0.4 Vertigo 1 0.4 DIAGNOSTIC WORKUP Mild to moderate increase in CRP and/or total leucocyte count 216 93 CT 111 43 CT + MR 120 47 Aspiration biopsy 7 3 DIFFERENTIAL DIAGNOSIS Retropharyngeal abscess 134 58 Spondylodiscitis 28 12 Meningitis 25 11 Neck artery dissection 4 1,7 COURSE Marked improvement within 2 weeks 221 95 Radiol Oncol 2023; 57(4): 430-435. Filipovic T and Avsenik J / Retropharyngeal calcific tendinitis review 433 methasone, 4 mg per os daily). The pain disap- peared within one week. Results The literature search returned no randomised controlled trials, meta analyses, clinical trials or systematic reviews. We retrieved a total of 198 ti- tles (Online Resources- 1 and 2), all of which were case and series reports and reviews. Of those, 112 were eligible for the study. The details of article selection are given in Figure 3. The total number of reported cases was 231. The results of literature analysis are summarised in Table 1. Discussion According to ICHD-3 criteria, RCT represents a “headache caused by inflammation or calcifica- tion in the retropharyngeal soft tissues”. The pain is usually severe, continuous, throbbing or elec- trising in quality. Trigeminal afferent fibres from dura and cervical afferent fibres from the skin and muscular tissue in the cervical region converge to synapse onto the same second-order neurons in the trigeminocervical complex. 9 This at least par- tially explains occipital (headache) and pharyn- geal (odynophagia) irradiation of the pain as well as neck stiffness (or decreased range of motion), as seen in our patients. Torticollis is sometimes reported, but may represent exaggerated neck stiffness. A detailed review of the (rare) causes of craniofacial and neck pain can be found in the lit- erature. 10 Little is known about the causes of calcium dep- osition or inflammation in the longus colli mus- cle. One report on histological findings in the re- tropharyngeal tissue of RCT patients has revealed a foreign-body type of inflammation around hy- droxyapatite crystals. 11 Immunological mecha- nisms involving the innate immune system in the form of new nerve growth and neovascularisation within the tendon in calcific tendinitis of the shoul- der joint have been reported. 12 Similar processes in the retropharyngeal space may be a plausible ex- planation in patients with RCT. However, further studies are needed to confirm these speculations. TABLE 2. Differential diagnosis of the Retropharyngeal calcific tendinitis (RCT) Feature RCT Meningitis Abscess Discitis Dissection GON,CH Neck pain +++ ++ +++ +++ ++ ++ Fever - + + + - - Photophobia - + - - - - Nausea - + - - -/+ - Decreased ROM +++ + (flexion) ++ ++ - -/+ Odynophagia ++/+ - ++ -/+ - - Long tract signs - - - -/+ + - CH = cervicogenic headache; GON = greater occipital nerve neuralgia; ROM = range of movement TABLE 3. Radiological clues for differential diagnosis Differential diagnosis Modality RCT ABSCESS TUMOUR X-RAY May show calcifications Prevertebral swelling - Prevertebral swelling CT Calcifications LCM oedema +Peripheral enhancement +Lymphadenopathy +Soft tissue mass (Variable enhancement) +Lymphadenopathy MR May suggest calcifications LCM oedema +Diffusion restriction (pus) (Superior contrast resolution) LCM = longus colli muscle FIGURE 3. Flowchart of article selection. Radiol Oncol 2023; 57(4): 430-435. Filipovic T and Avsenik J / Retropharyngeal calcific tendinitis review 434 Differential diagnosis includes other similar conditions that should be promptly recognised by neurologists (Table 2). Meningitis and meningoencephalitis are usu- ally accompanied by fever, photophobia, nausea and/or vomiting, or even an altered mental state 1 , not typically seen in RCT. They are also accompa- nied by neck stiffness, but only on flexion, not on extension or rotational movements. 1 Odynophagia is often seen in RCT, but is a hall- mark of retropharyngeal abscess, where in most cases, the blood count shows elevated leucocytes above 12 x 10 9 /l. 3,13 Spondylodiscitis, another pos- sible cause of acute severe neck pain, is usually accompanied by clinical and laboratory signs of systemic inflammation, and diagnosis is made af- ter appropriate imaging. 14,15 Spontaneous carotid or vertebral artery dissection could present as an isolated head and/or neck pain, sometimes accom- panied by nausea, but no neck stiffness has been reported. 16 Lastly, greater occipital nerve (GON) neuralgia and cervicogenic headache (CH), which are relatively benign conditions, characterised by prominent neck pain, should also be kept in mind1. 1,17 However, pain in GON neuralgia emerg- es in the form of short (seconds to minutes) attacks, leaving tenderness or allodynia in the region of GON. 1 Therefore, when pain evolves over a period of several hours or even days, other causes should be considered. CH is a broad category of chronic conditions, with some diagnostic criteria overlap- ping with RCT. Radiologically, differential possibilities in pa- tients with suspected RCT include retropharyn- geal abscess, tumour or even trauma; therefore, fa- miliarity with typical imaging findings facilitates early diagnosis and may prevent inappropriate therapeutic procedures (Table 3). As plain film radiography may miss subtle calcifications within the tendon, CT is the pre- ferred imaging modality due to its supreme reso- lution and multiplanar capabilities. 18 CT reliably confirms the location of calcifications within the superior fibres of the longus colli tendons and may show soft tissue swelling and/or small ret- ropharyngeal effusion as well. 19 Nowadays, the first imaging modality that these patients undergo is usually MRI, which demonstrates oedema and retropharyngeal effusion clearly. However, as cal- cifications are much subtler on MRI in comparison to CT, a high level of clinical suspicion is needed for the correct diagnosis. On the other hand, the presence of peripheral postcontrast enhancement or the evidence of pus on diffusion-weighted im- aging should suggest infection as the cause. 14 CT is immediately available and cheap but exposes the patient to ionizing radiation, which may be inap- propriate in women in the childbearing age. MRI is not as accessible as CT, is expensive, and lasts longer, which may pose a problem due to inabil- ity of the patient to lay still in the supine position. Finally, MRI may be contraindicated in the cases of metallic implants or claustrophobia. Conclusions RCT is a rare disorder that neurologists should be familiar with. It is also a relatively new subject for neurologists: it has been recognised as a neurolog- ic disorder only in 2013, when the ICHD-3 criteria were published. 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