Answer: Staphylococcus aureus

Mastitis is defined as inflammation of the breast. Although it can occur spontaneously or during lactation, this discussion is limited to mastitis in breastfeeding women, with mastitis defined clinically as localized, painful inflammation of the breast occurring in conjunction with flu-like symptoms (e.g., fever, malaise). Mastitis is especially problematic because it may lead to the discontinuation of breast-feeding, which provides optimal infant nutrition. Mastitis occurs in approximately 10 percent of U.S. mothers who are breastfeeding, and it can lead to the cessation of breastfeeding. The risk of mastitis can be reduced by frequent, complete emptying of the breast and by optimizing breastfeeding technique. Sore nipples can precipitate mastitis. The differential diagnosis of sore nipples includes mechanical irritation from a poor latch or infant mouth anomalies, such as cleft palate or bacterial or yeast infection. The diagnosis of mastitis is usually clinical, with patients presenting with focal tenderness in one breast accompanied by fever and malaise. Treatment includes changing breastfeeding technique, often with the assistance of a lactation consultant. When antibiotics are needed, those effective against Staphylococcus aureus (e.g., dicloxacillin, cephalexin) are preferred. As methicillin-resistant S. aureus becomes more common, it is likely to be a more common cause of mastitis, and antibiotics that are effective against this organism may become preferred. Continued breastfeeding should be encouraged in the presence of mastitis and generally does not pose a risk to the infant. Breast abscess is the most common complication of mastitis. It can be prevented by early treatment of mastitis and continued breastfeeding. Once an abscess occurs, surgical drainage or needle aspiration is needed. Breastfeeding can usually continue in the presence of a treated abscess.

The superficial inguinal ring is an opening in the aponeurosis of the external oblique just above and lateral to the pubic crest. The opening is oblique and corresponds to the fibres of the aponeurosis. It is bound inferiorly by the pubic crest, on either side by the margins of the opening in the aponeurosis and superiorly by the curved intercrural fibres.
The inferior crus is formed by the portion of the inguinal ligament that is inserted into the pubic tubercle.
The falx inguinalis is made of arching fibres of the transversalis fascia and the internal abdominal oblique muscle. It forms the posterior wall of the inguinal canal.
The internal abdominal oblique forms the root of the inguinal canal.
Scarpa’s and Camper’s fascia are the membranous and fatty layers, respectively of subcutaneous fascia.
Transversalis fascia covers the posterior surface of the rectus abdominis muscle inferior to the arcuate line.

In females, the breasts and lungs are the most common primary disease sites; approximately 80% of cancers that spread to bone arise in these locations. In males, cancers of the prostate and lungs make up 80% of the carcinomas that metastasize to bone. The remaining 20% of primary disease sites in patients of both sexes are the kidney, gut, and thyroid, as well as sites of unknown origin.

On contrast-enhanced CT scans, RCC is usually solid, and decreased attenuation suggestive of necrosis is often present. Sometimes, RCC is a predominantly cystic mass, with thick septa and wall nodularity.
RCC may also appear as a completely solid and highly enhancing mass

This patients is most likely experiencing an acute rejection. It is a cell mediated attack against the organ that has been transplanted. Antigens are either presented by blood borne cells with in the graft or antigen presenting cells in the body may be presenting class I and class II molecules that have been shed by the graft. Class I will activate CD8 and class II, CD4 cells, both of which will attack the graft.
Chronic rejection is a slow process which occurs months to years after the transplant. The exact mechanism is not very well understood but it probably involves a combination of Type III and Type IV hypersensitivity directed against the foreign MHC molecules which look like self-MHC presenting a foreign antigen.
Hyperacute Transplant Rejection occurs almost immediately and is often evident while you are still in surgery. It is caused by accidental ABO Blood type mismatching of the donor and recipient which almost never happens anymore. This means the host has preformed antibodies against the donated tissue.

A scaphoid fracture is a break of the scaphoid bone in the wrist. Symptoms generally include pain at the base of the thumb which is worse with use of the hand. The anatomic snuffbox is generally tender and swelling may occur. Complications may include non-union of the fracture, avascular necrosis, and arthritis.

Scaphoid fractures are most commonly caused by a fall on an outstretched hand. Diagnosis is generally based on examination and medical imaging. Some fractures may not be visible on plain X-rays. In such cases a person may be casted with repeat X-rays in two weeks or an MRI or bone scan may be done.
Scaphoid fractures are often diagnosed by PA and lateral X-rays. However, not all fractures are apparent initially. Therefore, people with tenderness over the scaphoid (those who exhibit pain to pressure in the anatomic snuff box) are often splinted in a thumb spica for 7–10 days at which point a second set of X-rays is taken. If there was a hairline fracture, healing may now be apparent. Even then a fracture may not be apparent. A CT Scan can then be used to evaluate the scaphoid with greater resolution. The use of MRI, if available, is preferred over CT and can give one an immediate diagnosis. Bone scintigraphy is also an effective method for diagnosing a fracture which does not appear on x-ray.

The long head of the biceps femoris arises from the lower and inner impression on the back of the tuberosity of the ischium. It inserts with the short head in an aponeurosis which becomes a tendon and this tendon is inserted into the lateral side of the head of the fibula and the lateral condyle of the tibia, thus crossing two joints.

The costodiaphragmatic recess is the lowest point of the pleural sac where the costal pleura becomes the diaphragmatic pleura. At the midclavicular line, this is found between ribs 6 and 8; at the paravertebral lines, between ribs 10 and 12 and between ribs 8 and 10 at the midaxillary line.
The cardiac notch: is an indentation of the heart on the left lung, located on the anterior surface of the lung.
Cupola: part of the parietal pleura that extends above the first rib.
Oblique pericardial sinus: part of the pericardial sac located posterior to the heart behind the left atrium.
Costomediastinal recess: a reflection of the pleura from the costal surface to the mediastinal surface, is on the anterior surface of the chest.
The inferior mediastinum: is the space in the chest occupied by the heart.

Osteomyelitis is most commonly caused by S. aureus in all age groups.

Dendritic cells are part of the immune system and they function mainly as antigen presenting cells. They are present in small quantities in tissues which are in contact in the external environment. Mainly in the skin and to a lesser extent in the lining of the nose, lungs, stomach and intestines. In the skin they are known as Langerhans cells.

Pyogenic granuloma (lobular capillary haemangioma) is a relatively common benign vascular lesion of the skin and mucosa whose exact cause is unknown
The name pyogenic granuloma is a misnomer since the condition is not associated with pus and does not represent a granuloma histologically. Pyogenic granuloma of the oral cavity is known to involve the gingiva commonly. Extragingivally, it can occur on the lips, tongue, buccal mucosa, palate, and the like. A history of trauma is common in such sites. The aetiology of the lesion is not known, though it was originally believed to be a botryomycotic infection. It is theorized that pyogenic granuloma possibly originates as a response of tissues to minor trauma and/or chronic irritation, thus opening a pathway for the invasion of nonspecific microorganisms, although microorganisms are seldom demonstrated within the lesion. Pathogenesis of pyogenic granuloma is still debatable.
Patients with pyogenic granuloma may report a painless glistening red lesion that bleeds spontaneously or after irritation.

The internal vertebral veins are the most likely route of metastasis as they are valveless. They serve an important clinical role as they are the route of free travel for cancerous cells to other body structures. The other veins on the list have valves and would be the least likely routes for metastasis.

Achalasia is a rare neurological deficit of the oesophagus that produces an impaired relaxation of the lower oesophageal sphincter and decreased motility of the oesophageal body. Achalasia is generally accepted to be a pre-malignant disorder, since, particularly in the mega-oesophagus, chronic irritation by foods and bacterial overgrowth may contribute to the development of dysplasia and carcinoma.
When oesophageal cancer develops in patients with underlying achalasia, diagnosis tends to be in the more advanced stages of cancer, compared to cases with no achalasia, because both physicians and patients often regard symptoms such as dysphagia and chest discomfort as attributable to the achalasia, rather than to other causes. Therefore, additional approaches that would lead to earlier diagnosis might be pursued less aggressively.
Achalasia is a predisposing factor for oesophageal squamous cell carcinoma.

Bile leak may be classified into a minor leak with low output drainage (<300 ml of bile/24 hours) or leaks due to major bile duct injury with high output drainage (>300 ml/24 hours).

The majority of minor bile leak results from Strasberg type A injuries with intact biliary-enteric continuity and includes leaks from cystic duct (CD) stump (55%-71%) or small (less than 3 mm) subsegmental duct in gall bladder (GB) bed (16%) and minor ducts like cholecystohepatic duct or supravesicular duct of Luschka (6%). An injury to the supravesicular duct occurs if the surgeon dissects into the liver bed while separating the gall bladder. This duct does not drain the liver parenchyma.
A leak from the cystic duct stump may occur from clip failure due to necrosis of the stump secondary to thermal injury/pressure necrosis or when clips are used in situations where ties are appropriate (acute cholecystitis) and in a significant majority from distal bile duct obstruction caused by a retained stone and resultant blow out of the cystic stump.
Strasberg type C and type D injuries usually present with a minor leak as well. The former results when an aberrant right hepatic duct (RHD) or right posterior sectoral duct (RPSD) is misidentified as the CD and divided because of the anomalous insertion of CD into either of these ducts.
Type D injuries are lateral injuries to the extrahepatic ducts (EHD) caused by cautery, scissors or clips.

High output biliary fistulas are the result of major transactional injury of EHD (Strasberg type E). Here the common bile duct (CBD) is misidentified as the CD and is clipped, divided and excised. This not only results in a segmental loss of the EHD but often associated with injury or ligation of right hepatic artery as well. Such devastating injuries are peculiar to LC and have been described by Davidoff as “classic laparoscopic biliary injury”.

Early recognition is the most important part of the management of bile leak due to iatrogenic injuries.
Unfortunately, most of the bile duct injuries are not recognized preoperatively. Optimal management of BDI detected postoperatively requires good coordination between the radiologist, endoscopists and an experienced hepatobiliary surgeon.

There is a scope of re-laparoscopy, within 24 hours of surgery, in situations where a low output fistula (<300 ml/day) is confirmed (by reviewing the operative video), to be because of a slipped CD clip. Through lavage, clipping or tying the CD stump with an endoloop may be a simple solution. Such an approach is not useful after 24 hours as inflammatory adhesions and oedema will make the job difficult. If low output controlled biliary fistula is detected after 24 hours, a wait and watch policy should be followed as many of the minor leaks will close within 5 to 7 days. If the leak fails to resolve or if the drainage amount is >300 ml/day (high output), an ERCP should be performed both to delineate the biliary tree and some therapeutic interventions if indicated.

Making up 4-5% of total body weight, the skin receives approximately 2% of cardiac output.

Nasal discharge of clear fluid and a recent head injury makes basal skull fracture the most likely underlying cause for facial nerve palsy.

Facial palsy is a neurological condition in which function of the facial nerve (cranial nerve VII) is partially or completely lost. It is often idiopathic (Bell’s palsy) but in some cases, specific causes such as trauma (e.g. temporal bone fracture), infections, or metabolic disorders can be identified. Two major types are distinguished:

1. Central facial palsy—lesion occurs between cortex and nuclei in the brainstem
2. Peripheral facial palsy—lesion occurs between nuclei in the brainstem and peripheral organs

Diagnosis can usually be made clinically while patient’s history often helps in evaluating the underlying aetiology.
Patients with basal skull fracture following head injury (as in this case) exhibit Battle’s sign on examination. It is an indication of fracture of middle cranial fossa of the skull and consists of bruising over the mastoid process as a result of extravasation of blood along the path of the posterior auricular artery. Clinical presence of CSF leak further supports the diagnosis.

Assessment options for basal skull fracture include CT and MRI scan. Idiopathic facial nerve palsy is treated with oral glucocorticoids and, in severe cases, with antivirals. Treatment of the other types depends on the underlying cause. Prophylactic antibiotics are given in cases of CSF leak.

The endocardial cushions in the heart are the mesenchymal tissue that make up the part of the atrioventricular valves, atrial septum and ventricular septum. An incomplete fusion of these mesenchymal cells can cause an atrioventricular septal defect. The terms endocardial cushion defect, atrioventricular septal defect and common atrioventricular canal defect can be used interchangeably with one another.

According to Bohr’s equation, VD/VT = (pA(CO2) − pE(CO2))/pA(CO2), where pE(CO2) is mixed expired CO2 and pA(CO2) is alveolar CO2pressure. Normally, the pa(CO2) is virtually identical to pA(CO2). Thus, VD/VT = (pa(CO2)) − pE(CO2)/pa(CO2). By Fowler’s method, VD/VT= 0.25. In the given problem, (pa(CO2) − pE(CO2)/pa(CO2) = (40 − pE(CO2)/40 = 0.25. Thus, pE(CO2) = 30 mmHg. If there is a great perfusion/ventilation inequality, pE(CO2) could be significantly lower than 30 mm Hg, and the patient’s physiological dead space would exceed the anatomical dead space.

Answer: Epstein-Barr virus

The Epstein–Barr virus is one of eight known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. Infection with Epstein-Barr virus (EBV) is common and usually occurs in childhood or early adulthood.
EBV is the cause of infectious mononucleosis, an illness associated with symptoms and signs like:
fever,
fatigue,
swollen tonsils,
headache, and
sweats,
sore throat,
swollen lymph nodes in the neck, and
sometimes an enlarged spleen.

Although EBV can cause mononucleosis, not everyone infected with the virus will get mononucleosis. White blood cells called B cells are the primary targets of EBV infection.
Petechiae on the palate are characteristic of streptococcal pharyngitis but also can be seen in Epstein–Barr virus infection, Arcanobacterium haemolyticum pharyngitis, rubella, roseola, viral haemorrhagic fevers, thrombocytopenia, and palatal trauma.
Despite the fact that infectious mononucleosis is a self-limiting disease, it may cause serious and lethal complications. The mechanism of splenic rupture secondary to infectious mononucleosis has been controversial. It is commonly believed that it is caused by an increase in intra-abdominal pressure or contraction of the diaphragm with vigorous cough, vomiting and defecation, leading to a compression of the spleen. However, Patel et al. argue that it is primarily the result of an expanding subcapsular haematoma which subsequently tears the capsule and leads to hemoperitoneum. Traditionally, rupture of spleen is treated by splenectomy. The rationale is to prevent the chance of sudden death as an early complication of splenic rupture and the risk from blood transfusion.

Sialolithiasis (also termed salivary calculi, or salivary stones), is a condition where a calcified mass or sialolith forms within a salivary gland, usually in the duct of the submandibular gland (also termed Wharton’s duct).
Signs and symptoms are variable and depend largely upon whether the obstruction of the duct is complete or partial, and how much resultant pressure is created within the gland.
The development of infection in the gland also influences the signs and symptoms:
– Pain, which is intermittent, and may suddenly get worse before mealtimes, and then slowly get better (partial obstruction).
– Swelling of the gland, also usually intermittent, often suddenly appearing or increasing before mealtimes, and then slowly going down (partial obstruction).
– Tenderness of the involved gland.
– Palpable hard lump, if the stone is located near the end of the duct. If the stone is near the submandibular duct orifice, the lump may be felt under the tongue.
– Lack of saliva coming from the duct (total obstruction).
– Erythema (redness) of the floor of the mouth (infection).
– Pus discharging from the duct (infection).
– Cervical lymphadenitis (infection).
– Bad Breath.
– Rarely, when stones form in the minor salivary glands, there is usually only slight local swelling in the form of a small nodule and tenderness.

Serine protease coagulation factors include: thrombin, plasmin, Factors X, XI and XII. Factor VIII and factor V are glycoproteins and factor XIII is a transglutaminase.

The sympathetic nervous system regulates vascular tone, dilation of pupils, arrector pili muscles, sweat production and visceral reflexes. Neurones that supply the voluntary muscles originate from the ventral horn of the spinal cord. If these nerves were thus damaged, these functions would be impaired. The sympathetic nervous system is not responsible for voluntary muscle activity.

Breast cysts are common and are smooth, firm, mobile lumps that can sometimes be tender. Cysts can also be bilateral and are known to recur in 10% of cases. They are more common in women in the third and fourth decades and most often disappear after menopause. Cysts are filled with fluid from the breast which occurs due to the normal menstrual cycle of a woman. The end of the menstrual cycle causes breast cells to swell. After the menses, the cells shrink and the released fluid disappears. However, in some cases this fluid forms a cyst. Incidence of cysts was also linked to use of oral contraceptives.

Under the influence of oestrogen in pregnancy, there is an increase in the number of lobules which will facilitate lactation.
Steatocytes occur due to loss of weight and nutritional deficit.
Metaplasia is a normal physiological process which is due to a change in normal epithelium with another type.
Lobular atrophy will result in a decreased capacity to provide milk.

Worldwide, approximately 500,000 new cases of cervical cancer and 274,000 deaths are attributable to cervical cancer yearly. This makes cervical cancer the second most common cause of death from cancer in women. The mainstay of cervical cancer screening has been the Papanicolaou test (Pap smear).

The posterior cruciate ligament is attached to the posterior intercondyloid fossa of the tibia and the lateral and front part of the medial condyle of the femur. It resists sliding of the tibia posteriorly.

The first brachial arch (mandibular) gives rise to the mandibular and maxillary processes. Muscles and bones of this process originate within the arch’s mesoderm. The first arch cartilage (Meckel’s) ossifies to form the incus and malleus of the middle ear. Its perichondrium gives rise to he sphenomandibular ligament and through intermembraneous ossification after the mandible forms, the rest of the cartilage disappears. Muscles of the first arch include: mylohyoid, tensor tympany and palati, temporalis, masseter and lateral pterygoids and the anterior belly of the epigastric. This first arch is supplied by the trigeminal nerve.

The posterior interosseous nerve which causes, what is known as the posterior interosseous nerve syndrome. The nerve is compressed before it bifurcates to form the medial and lateral branches. The compression is beyond the origin of the branches to the radial wrist extensors and the radial sensory nerve. The result of such a case is paralysis of the digital extensors and the extensor carpi ulnaris, resulting in dorsoradial deviation of the wrist.

The posterior drawer test is a physical exam technique that is done to assess the integrity of the posterior cruciate ligament (PCL). The PCL is attached to the posterior intercondylar area of the tibia and passes anteriorly, medially, and upward to attach to the lateral side of the medial femoral condyle.
This ligament prevents backward displacement of the tibia or forward sliding of the femur. Injury to the ligament allows displacement of the tibia

The medial and lateral circumflex arteries are direct branches of the Profunda femoris artery otherwise also known as the deep artery of the thigh. The Profunda femoris artery arises from the femoral artery just below the inguinal ligament (approximately 2-5cm below it).
The following are the branches of the deep artery of the thigh:
Lateral circumflex femoral artery
Medial circumflex femoral artery
Perforating arteries

90 – 95% of the bile salts are absorbed from the small intestine (mostly terminal ileum and then excreted again from the liver. This is known as the enterohepatic circulation. The entire pool recycles twice per meal and approximately 6 to 8 times per day.