Friday 3 July 2020

Corona and Chest Imaging

COVID 19 stands for Corona virus disease 2019.
It’s a highly contagious disease caused by severe acute respiratory syndrome corona virus 2, SARS COV 2, a race of corona virus.
Initial cases were seen in Wuhan of China in late December 2019 with the rapid spread of disease globally and came up as a pandemic affecting more than 10 million people worldwide. 
Non-symptomatic carriers and asymptomatic transmission is a major cause of poor control over the disease.

Disease transmission is primarily human-to-human as of now,  transmitted similarly as the common cold, via contact with droplets of infected individuals during sneezing, coughing or even speaking. 

The suggested incubation period of the disease is approximately five days, almost all developing symptoms typically 14th day after the exposure to the virus. Fortunately, the death rate of the disease is only 2 to 3%. Furthermore, it is speculated that the death rate is much lower than that because asymptomatic or mildly symptomatic cases are not being tested and included in the statistics, apparently showing the high death rate.
It is interesting to mention that 60% of patients affected are male with high predominance between 45 to 60 years of age. Older age is known for increased mortality. Children across the globe relatively found spared by the disease. However, critically ill children under 12 years of age and infants are known as well in certain corners of the world with a shorter incubation period of about two days compared to adults.

Clinical presentation is typically systemic or respiratory. Gastrointestinal or cardiovascular symptoms are very uncommon. Common symptoms in the descending order are fever 85-90%, cough 65-70%, fatigue, shortness of breath, body pain, headache, sore throat, shivering with associated nausea vomiting.
Patients presenting with palpitations, chest tightness, urinary tract infection, diarrhoea are also known.

RT-PCR Swab test 

A positive RT-PCR test needed for a definitive diagnosis of disease.
Its real-time reverse transcriptase-polymerase chain reaction (RT-PCR) test, is highly specific, but with sensitivity reported as low as 60-70%. Thus, false negatives are a real clinical problem so several negative tests might be required to be confident about excluding the disease.
A false-negative rate of 100% on the first day after exposure, dropping to 67% on the fourth day. On the day of symptom onset approximately 4 days after exposure, the false-negative rate remains at 40 %, and it reaches its lowest to 20% at around three days after symptoms during which test has the highest accuracy. After this again the false-negative rate increases reaching 66% on day 21 after exposure. 

Role of CT chest

CT findings were not part of the diagnostic criteria for COVID-19. However, CT findings have been used controversially as a surrogate diagnostic test by few including me being fast and highly sensitive. 
I would like to mention that CT is not recommended for follow-up imaging to assess disease progression. Chest X-ray is considered to be the best for bedside follow-up in this regard. However, chest Xray is much less sensitive than chest CT, so its very common to have normal chest Xray in early or mild disease. 
CT Chest with typical GGO

Normal Chest Xray of the same patient 

CT protocol is non-contrast spiral chest CT. Iodinated contrast medium is only indicated when one need to do CT pulmonary angiogram (CTPA) for suspected pulmonary thromboembolism.

Primary findings of COVID-19 on chest radiograph and CT are those of atypical pneumonia or organizing pneumonia. The most frequent is airspace opacities, often described as consolidation and ground-glass opacity, often bilateral, peripheral, and lower zone predominant. Fibrotic bands and traction bronchiectasis can be seen when the disease is resolving.
Pleural effusion and lymphadenopathy are rare, rather they are not the features of the disease.

Other common ancillary lab tests which are performed in a hospitalised patient are CBC for lymphopenia, increased prothrombin time (PT), increased lactate dehydrogenase, CRP, ESR, D-dimer, serum amylase. Mildly deranged liver function tests are common, primarily elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Alkaline phosphatase (AKP) and gamma‐glutamyl transferase (GGT) levels remain normal.

Complications during the disease which contributes in mortality are acute respiratory distress syndrome (ARDS), acute thromboembolic disease, pulmonary embolism, acute cardiac injury due to elevated troponin levels, myocardial ischemia, cardiac arrest, myocarditis. These complications are more common when there are associated comorbidities like obesity, older age, and diabetes.

Rx, no definitive treatment or vaccine exists as of now however, dexamethasone, a kind of steroid has a crucial role in changing the outcome of clinically bad patients. Antiviral therapy such as Tab Fabiflu recently launched in the market and is available with a prescription.

Spinal Osteoid osteoma

Osteoid osteoma

A benign bone tumour, typically occurs in children and adolescents, more common in males. Characteristically present with night pain which is relieved by the use of salicylate analgesia such as aspirin.
They are a classic cause of painful scoliosis when occurring in spine, concave on the side of the lesion. Soft tissue swelling and oedema may occur and if close to a growth plate, accelerated growth may be evident, may be related to hyperemia.
Most osteoid osteomas occur in long tubular bones of the limbs such as femur and tibia.
The femur is the most common location especially the neck of femur. The mid-tibial diaphysis is the next common location.

Osteoid osteomas are usually cortical lesions with adjacent sclerosis which is reactive and does not represent the lesion itself. 
The nidus is usually less than 2 cm in diameter and is typically ovoid in shape. Associated solid periosteal reaction with cortical thickening on x-ray or CT. The nidus is sometimes visible as a well-circumscribed lucent region, occasionally with a central sclerotic dot. 

CT is excellent at characterizing the lesion and is the modality of choice. 

Nuclear medicine, skeletal scintigraphy will show typical focal uptake and at times will show a double density sign.

MRI is sensitive, but is non-specific and is often unable to identify the nidus due to associated bone marrow and adjacent soft tissue oedema.

The lesion is benign and treatment has traditionally been with surgical resection. 

General imaging differential considerations include:

osteomyelitis, Brodie abscess
osteoblastoma more than 2 cm in size
stress fracture
cortical desmoid
localized cortical thickening
intracortical hemangioma

Posterior Mediastinal Cyst

Clinically: patient presented with low back pain.
No posterior mediastinal symptoms or signs.

A well-defined unilocular cystic lesion measuring approximately 20 mm in posterior mediastinum adjacent to the dorsal spine at D4 – D5 level at 11 o'clock position on axial sections. No obvious adjacent osseous involvement or intraspinal extension.
Rest of the MRI WHOLE SPINE screening unremarkable.

Imaging diagnosis: 
Appears an incidental non-tumoural posterior mediastinal cyst-like Mullerian cyst.
No associated vertebral anomaly to suggest Neuroenteric cyst. The lesion is not close to trachea or oesophagus to suggest duplication cyst. Rest of the sag T2w screening MRI study of the Whole spine shows no significant abnormality in cord or cauda equina.

Cystic lesions found in the mediastinum are typically included bronchogenic cysts, esophageal duplication cysts and Neuroenteric cysts.
But typical Mullerian cysts of this kind also needs consideration which is often overlooked.

The reason may be Mullerian cysts in locations outside of the female pelvis are rare. Some reported locations include the skin and retroperitoneum. The etiology of Mullerian cysts arising in the mediastinum is unclear. Batt suggested that the lesion is derived directly from the primary Mullerian apparatus.
While only 14 cases of mediastinal cysts with Mullerian differentiation have been described in the literature, it is likely that they are much more common than presumed in older females and often misdiagnosed as either bronchial or oesophagal cysts. 

The fourteen definitive mediastinal cysts with Mullerian differentiation have been identified, have occurred in females 40-60 years old. These patients typically presented with cough or were asymptomatic. All cysts were paravertebral in location, occurring between T3-T8 vertebrae. All of the cysts were positive for either ER or PR. Our report is the first to show expression of PAX8 and WT1, both markers of Mullerian differentiation, in these cysts.

The other DDs for cystic masses of the posterior mediastinum include:
bronchogenic cyst
esophageal duplication cyst
neuroenteric cyst
mediastinal thoracic duct cyst
mediastinal pancreatic pseudocyst.